-
FISHERIES RESEARCH BOARD OF CANADA
Translation Series No. 1503
Toxicological and biochemical research of pesticides using radioisotopes.
By Junichi Fukami
.Original titl: RI riyo ni yOru Noyaku no Yakuri-to Seikagaki. U - '
From: Hoshseibushiteu (Radioisotopes), 18 (9): 385-401, 1969.
.Translated by the ,TranslatiOn Bureau (MI) , FOreign Languages Division - Department of the Secretary of State of Canada
Fisheries Research Board of Canada Freshwater Institute Winnipeg, Manitoba
1970-
68 pages typescript
-
TRANSLATED FROM - TRADUCTION DE INTO - EN
Japanese. English
PAGE NUMBERS IN ORIGINAL NUMROS DES PAGES DANS
L'ORIGINAL
PUBL ISH ER - EDIT EU R
no clue available to identify DATE OF PUBLICATION DATE DE PUBLICATION .
385 - 14 01 ISSUE NO. NUMRO
YEAR AN- NE
VOLUME PLACE OF PUBLICATION LIEU DE PUBLICATION
NUMBER OF TYPED PAGES NOMBFtE DE PAGES
DACTYLOGRAPHIES
18 no clue available to identify 9 1969 1 - 68
M. I .
28.7 .70
Fe-e /5 o3 DEPARTMENT OF THE SECRETARY OF STATE
.. TRANSLATION BUREAU
FOREIGN LANGUAGES DIVISION , CANADA
SECRTARIAT D'TAT BUREAU DES TRADUCTIONS
DIVISION DES LgANGUES TRANGRES
AUTHOR - AUTEUR
FUKAMI, Junichi
TITLE IN ENGLISH - TITRE ANGLAIS
Toxicological and Biochemical Research of Pesticides Using Radioisitopes Title in foreign language (transliterate foreign charaetera)
RI riyo ni yoru Noyaku no Yakuri to Seikagaku
REF5RENCE IN FOREIGN I,ANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE FOREIGN CHARACTERS. REFERENCE EN LANGUE ETRANGERE (NOM DU LIVRE OU PUBLICATION), AU COMPLET.TRANSCRIRE EN CARACTERES PHONETIQUES.
possible)
Hoshaseibushiteu (or Hoshano bushitsu, Hoshasengaku)
REFERENCE IN ENGLISFI - RFRENCE EN ANGLAIS
Radioisotopes
REQUE.STING DEPARTMENT Fisheries & Fores try MIN ISTERE-CLIENT
TRANSLATION BUREAU NO. 1061 NOTRE DOSSIER NO
BRANCH OR DIVISION DIRECTION OU DIVISION
PERSON REQUESTING DEMANDE PAR
Fisheries Research Board
Dr. Jack Uthe, Freshwater institute. Winnipeg, Man.
TRANSLATOR (INITIALS) TRADUCTEUR (INITIALES)
DATE C.OMPLETED ACHEVE LE
YOUR NUMBER 769.-18-14. VOTRE DOSSIER N
DATE OF REQUEST 13.5.70 DATE DE LA DEMANDE
SOS-200-10.8 (R EV. 2/014
-
CANADA
Review Article /385
DEPARTMENT OF THE SECRETARY OF STATE
' eTRANSLATION BUREAU
FOREIGN LANGUAGES DIVISION
, f / 5-0 SECRTARIAT D'TAT
BUREAU DES 'TRADUCTIONS
DIVISION DES LANGUES TRANGRES
CLIENT'S NO. DEPARTMENT ' OIVISION/BRANCH cm, ' N9 OU CLIENT MINISTERE DIVISION/DIRECTION VILLE
769,- 18-14 Fisheries & Forestry. Fisheries .Research Board'Winnipeg Mari
BUREAU ND. L.ANGUAGE .TRANSLATOR (INITIALS)' MMrE No DU BUREAU LANGUE . TRADUCTEUR (INITIALES)
1061 Japanese . M.I... 29 Jule-1970
TOXICOLOGICAL.AND BIOCHEMICAL RESEARCH OF PESTICIDES USING'
RADIOISOTOPES -
. by .
Junichi FUKAMI
Laboratory of . Entomological Toxicology
Riken (Institute of Physical and Chemical Research)
Radioisotopes Vol. 18, No. 99 PP. 385-401 (1969)
Translator's Note: Table of Contents was added for clarity.- Some figures and chemical structures:were misprinted, and therefore they were rewritten, referring to:other chemical literature. The authOr mixed English terms, in phonetic writing ., .with German terms and they were translated into English. Some reference numbers in the text were misprinted, and by checking the authors' names, some could be . corrcted. A few could not be locate d . in the text,.while a few others were illegible (foot notes). The translator did obtain the author's address:.
Riken, YamatomaChi, Kitaadaphi, Saitama, Japan..
UNEDITED DRAFT TRANSLATION Orily for information
TRADUCTION NON REVISE .nforrnzCien soule.ment
SOS-200-10-31
-
II
(397)
(398)
.40.
CONTENTS
. . . . . Page (Original . . . . ..
1 introduction - 2 . (385)
. .
*. ". ' .2- Insecticides - 7 (386)
2.1 Insecticides ' . .. . . 7 . 0 ..
' 2:1.1 Rotencids . . 7
2.1.2 Pyrethroids- . 12 . (387)
2.2 OrganphOsphates 16 (388)
2.2.1 Exchange Reactions between S and 0
2.2..2 Oxidations of Sulfur
2.2,3 Hydroxylations of Alkyl Side Chains and N-dealkylations
2.3 Carbamate Insecticides
2.4 Organochloro Insecticides
2.5 Inductive Avtivation of Drug-oxidizing Enzymes by Organochloro Insecticides 36 (392)
3 Weedkillers 39 (393)
3.1 Trifluralin 40
3.2 Diphenamide 40
3.3 Diuron, Monuron 41
3.4 Dicamba 43 (394)
3.5 Paraquat, Diquat 44
3.6 Simazine, Atrazine 45
3.7 Propanil (
47 (395)
3.8 Naphthaleneacetic Acid 49
4 Fungicides 50
5 Selective TOxicity 56
5.1 Selective Tocicity of Rotenone 56
5.2 Selective Toxicity of Parathion Type Insecticides 60
Bibliography 65
., .22
., 24
.. 31
-
2 -
I. INTRODUCTION
The remarkable advances in developing various pesti-
cides together with the steady improvements of agricultural
technology in the recent years resulted in almost consecutive
increases of annual crops of rice and yields of other agri-
cultural products, particularly fruit and vegetables. The
consumption of pesticides in this.country also increased
enorMously in -recent years. In fact, the increment could e
. figured out from the difference in 'total output 's of pesticides,
*four billion Yens* .in . 1951 and Sixty-seVen billion and one
..hundred million yens* in 1967. Of these pesticides produced,
More than .90% of the products** ar.organic-chemically synthesized
compound. The pesticides comMonly used.during abd before the -
war*** were either natizral organic compounds such as - rotenoids
and. pyrethroids Or inorganic compounds', for example, - arsenic
chemicals. Consequently, nobody had shown interest in cumulative
or residual toxicity of the pesticides. However, many organic
synthesis products including DDT, BHC, parathion, 2.4-D,
organomercuric preparations and others became the more common
pesticides fter the war. While these synthetic organic
pesticides became popular, the unfavourable effects on the
general health of human beings also started to appear. These
*Translator's Note: 4,000,000,000 yens and 67,100,000,000 yens. 330 yens = 1 Canadian dollar.
** " " 90% of the kinds of product or of the total amounts?
*** " referring to W.W. II.
-
3 --
effects are indeed the . dark , side of the application -of
pesticides-, and thy'include i.e. the' poisoning .of users
of the pesticides, pesticide reeidties in the agricultural.
prOducts,,and . destruction of useful predatory'insects and.
animals. R.C. CarSon's "Silent Spring" (translatedinto
: Japanese" Sei to Shi no Myoya1u",.1962) 1). and the Yesner
, Report 2) of-America aroused the common intereSti_n the .
secondary . effects 0' pesticides,. emphasizing that in order
to reduce the unfavourable side effects of pesticides, safer,
and selective.methods of removing unwanted insects should .
be developd. They suggested that (a)*theuse of.selectively
toxic compotinds, (h) compounds Which did not leave residual -
matter, (c) application of methods which were selective in
use or' (d) the use of attractants and,cheMicals which inter-:
fered only with reproductiOn-, and further development of
methods whiCh did'not use ' any . chemical at all; might be.the
solutions. - In order to expioreHthese suggested methods, it
is.important.to study the mechanism.of the action of:pesti-:
ides, namely, their comparative toxicities, the metabbliems
in insects,. mammals, and Plante:1w- Understanding -Ole processes
. of the pesticides to *be . decompoeed and deactivated in nature :
is aleo one of the more important basic:problems to be studied.
In . gener1, newer methods.of removal of . insects are expected
to be derived from the resulte of the studies of baeic .
problems rather than from cumulating . experiences'only. These
-
studies shouId.aIso yield helpful:improvements and solutions
in removal of the insects which were rapidlibecoming resistant.
to the-existing.insecticides i. The 'author has been Working in
one of:thselasic problem areas, particularly the selective' . .
insecticidal aCtion of insecticides l *for . some.years. Although
their 'margins of selectivity are rather . wide, we - have already
found some insecticides which have a very low toxicity -fr
mammals and-destrby only the harmful insects. The diffrence
in the'activities of these insecticides - against insect and ,
maffimals is mostly depending.on . the qualitative and quantitative
differenCes of the metabolism systems of thee living'creatures.
TheMetaboiisms of the-pesticides'and other chemicals are, .
mainly, depending on the action of their ' enzymes. Therefore
the result of the, se enzyme actions - activation and deacti-
vation of pesticides --appear to yield the .width of the
margins of selectivitY of' the peticides. The firt step
in the metabolism'of the pesticides introduced into the body '
is'probablY oxidationreduction and hydrolysis, and the
second tep is the formation.of complexes of their primary .
.metabOlism products. The proceses - and the -mechanisms have
been explored mainly by using pesticides labeled mith radio
isotopes....This,author intends to ipreSent examples of
applications of radioisotopes mainiy'in the studies of-
oXidative metabolism,.which has been most .carefully studied
and further, explain their applications in hydrolysis and
*complex formation reaction. It wouldplease the author
-
greatly'if.this article could arouse the interest of those
who were engaged in the studie of the areas not directly
related to the pharmacology of insects.
As for th oxidation of the Chemicals, it:isWell
. known that tWo systems 'aire participating . in biological . ,
oxidations.one is - the enzyme system which oxidizes the
substrate in the mammalian liver microsomes in the presence
of NADPH* and pkygen, and the other i the system which includes -
.c.itoChrome P-450.. The chemicalsubtances, once introduced .
into the biological systms, are.oxidized by oxidation. enzymes, -
and the oxidation products further undergo Various complex.
, formations, for instance, acetylation, sulfonate 'ester
formation end gIucuronide formation. When fUnctional groups
that are 'harmful to biologiCaI metabolisms are masked .by
derivative formations, the deriVatiVes.are also - easily .brought
into.the excretory systems4'The major types of metabolisms -
which are carried out by the enzymatic .oxidations are (1) .
oXidation of alkyl side chains, - (2) hydroxylation of aromatic .
rings, (3) hydroxylation , cif non-aromatic rings, (4) dealkylation
ofN,alkyl compounds,. (5) dealkyIation of-Oalkyl compounds
(6) 'oxidation of amind - groups '(N-pxidation) (7) oxidation 'of
sulfur (sulfoxidation),..and (8).exchange reaction between -
*Translator's Note: Some 'authors use NADPH2 (reduced.nicotine adenine dinucleotide phosphate;'formerly TPNH). See also NADH in section 2.1.1. Some authors use NADH2 (reduced nicotine adenine dinucleotide; 'formerly DPNH).
-
S and O. Which type or .tyPes of oxidative metabolism take ...
place.when psticidesare . introduced - lnto biologial systems,
that is; the'selection of the type s. of metabolism, is not
. clearly understood. This difficult prediction is Mainly
because of the fact that the pesticides are applied against
many species of .mammals, fish, insect, plant and microbe,
and as. a result, just what kinds of oxidation enzyme exist
'in each species of living-creatures to oxidize certain kinds..
of pestiids is quite uncertain.. Even such a seeminglY simple
question as Whether eome species of insect's have - the - Same
kinds of oxidation enzyme as.foundin mammalian, liver micro-
somes has not been answered witn'reasonable - accuracy..Questions
such as this and the effort to answer the 'questions appear
. to .give the more vital drivingfprce and to orient the
direction in discovering the more .. .selective pesticides.
Dedigning of better qualified pesticides May be achieved /386
only by understanding the mechanism of the pesticidal . action
in each case Of applicatiOn.,
The author plans to explain the examples of application
of radioisotopes in the mechanism studies of insecticidal
actions, as this area is one of the most advanced of all the
pesticide studies, and . then to describe the studies in other,
areas in the order of weedkillers and fungicides.
-
. INSECTICIDES
2.1 Natural Insecticides r
. 2.1.1 Rotenoids
. Rotenone, the major component of derria root * , hae
been widely used'as a. natural insecticide -since before the -
war. Rotenone_has a low toxicity in mammals but its toXicity .
against.fish and a variety of inseCts,but'not all, 'is quite .
high. It has been said that the ideal insecticides are the
compounds which have both-the lethal action . of rotenone and
the paralytic action of pyrethroids. Therefore the pharma-
cological importance of the studies on rotenClids lies in the
action mechanismof totenone, the relationship between the
chmiCal structuree and physiological activities of totenone
derivatives, and the cause of the selectivity, of the toxicities
of rotnoidb.. .
As for the action mechanism of rotenone, blocking
of the activity of mitochondrial L-glutamic dehydrogenase
3,4) by rotenone was first pointed out , and later the
blockage was narrowed down to the NADH enzyme system. The
latest tudies proved that the blocking took place speci-
fically at the coupled oxidation of NADH and a ubiquinone**,
as shown in figure 1 577) .. The mechanism of the blocking at
this site of blockage was also studied using 14 -rotenone8) .
* Translator's Note: Derris elliptica, common in Malaya. tt ** or NADH 2 and a flavoprotein.
-
7 8
-
O .
Rote n (me. - Rote ri One: c(e h'freiVires
-
V D H N IDN de. b,rdrofe eur set Co Q Cyt Cyt
lk s-44..cce n . deltraroje mase
Fij. I: Si-tes of chi ri of kofeno ids ( crtYro )
Since the site of action.rotenonoidS is.probably
the same in fish, insects and Mammals, the selectiVity of
the rotenoids must be caused before the rotenoids reach, this
si te. The metabolism . of 14 -rotenone and-its selective C
toxicity against different kinds of living.crattires have
been studied by Fukami and others 9 ' 10) When 14 -rotenone
was .reacted with rat liver microspmes and NADPH as an
auXiliary enzyme in the -atmosphere, almost all the rotenone
was metabolized. Pive* major metabolic prodiicts which were
soluble in ether wereas shown in Figure 2,.hydroxylation
products at the isopropenyl side chain . and at the Junction
of B and C rings. When the same 1.4d-rotenone metabolism
was studied in vitro, .using liver Microsobes of mouse and
*Translator's Note: 4 in Figure 2. 8 in the preceding chart.
S L-CC C a. ci. ct
-
carp, abdominal microsomes of diazinone-,resistant houseflies,
. and those of the Wamon (or ring) . dockrbach'exactly the same
.hydroxylaticn products:as- found in the - rat livr'microsome
expriment wer detected,.and no qualitative difference
could be detectecLamong the metabolites. At the:same time,'
a series. of in vivo - experiments '1,,?ere - conducted by administering
14 0-rotenone to the various living'creatures aformntioned,
and the metabolism products were examined, by extracting
various organsof the aubstrate and their . urine samples. .
with ther. he ether soluble metabolites were found to be
cmpletely identical:hydroxylation products as found . by
'in vitro experiment. Furthermore; the biological activities.
'of . these hydroxylated products were much . weaker_than the .
starting material, rotenone,, and, therefore it was assumed
that the oxidative metabolisM of rotenOne is a type of .
detoxication.
8'-hydroxy 8'..-hydroxy 8'-hydroxy: rotenolone II rotenone rotnolone I
I rotenolone II 4-- rotenone -) rotenoldne I
1. I 6',7'2dihyclro- 6',7 1-dihy- droxy roxy rotenolone I rotenolone II rotenone
Metabolites of rotenone
-
10 -
C H30 OCH
I 3 roteV\0131ete. I Oh
rOtehOlOner. Oh
cH z.
d14 2. 0H CHz0H
OH 113
22 : 1'4 eta. boh's yn of Rote none tr/o-, in vitro)
Ilacaled 17).- them s cx.tor .
HO
8 I e
O H
0 o
P ky ct r-o), rote n one.
H r- 2 ( c H3 ch, hyaroxy rote n o he,
-
As will be discussed in the section on pyrethroids,
piperonyl butoxide 11) , egonol12Y 1 sesame oil 13) and other
methylenedioxyphnols increase the insecticidal activity
of rotenone, nad therefore these compounds are insecticidal
synergists. It is also known that piperonyl butoxide,
sulfoxide, MGK 264 amd SKF-525A inhibit in vitro hydroxylation
of rotenone via the microsome - NADPH - oxidase system, These
findings indicate that the oxidative degradation of rotenone
by the mdcrosomes plays a significantly important role in
understanding the metabolisM of:rotenone in biological systemslo)
When in vitro liver-microsome-MADPH systems including rotenone
are prepared using rat., mouse.and carp lVers, and to each
system, supernatant of the corresponding liver extract is
added, the degration. prOgress beyond 'the:aforementioned
hydrooxylation stages,.prodUcing water-soluble mtabolites
by further transformation of the ether-solubie hydroxylation
prOdUcts. This finding leads to a hypotheis that the se-
condary metabolism products of rotenone probably yield a
variety of their functional derivatives which . themselVes
aid the exCretion. and .degradation of rOtenome1 .0) .. The
author plane t explain this hypothesis in more'details,
in the section on selective tOxicity of rotenone, near th
end of thie article.
-
- 12 -
O CH (0 CHI C H2)z. o C2 Hs- i CH3
sesa.kne X CHa C HC
112 (C CH1 0)z Ce,i H9
pifret-ony/ at-oxiWe
I It ci Hs- o
c- c-ocitz n N 2 I 2. fis-CI Hz C H3
S tc-F
Tian 5 letto Noie : All the siruciu.re s are corrected by the Mule inhrY
2.1.2 Pyrethroids
Pyrethrin has remarkablY distinct advantages in that
it is fast-acting and that itsi toxicity for mammals is sur-
prisingly . low, but it has the unfavourable property of per-.
mitting rather quick recovery of victims. The mechanism of
'its insectiidal_ . actiOn has hot been clarified yet. Phama-
cological interest in pyrethroids can be summarized in their
rapid paralytic action, low toxicity against mammals, and the
mechanism of their action. .
-
r 13 -
The . activities..of pyrethroids apPar to te': caused-
by two.partiai . structural fragment,:one bing cyclopropane-
'carboxylic acid moiety which contains an 'unSaturated side.
chain and the'other, cyclopentanolne which is also :
functionalized by an unaaturated :alkyi sid:chin..It is
said -that,.. - if.a slight modification is made in either One '
of these, acid and alcohol of pyrethrOids,: theiractivitie
are often remarkablilowered. .It has been also Said .that,,
in the detoxicative metabolism of pyrethroids, hydrolySis
of the ester linkage plays the most important . role. However,
the experimental results.obtained by applying 14 . -pyrethrin14).9
C ). ' allethrin -15 , and 14 -pyrethrin-I and -cinerin-I
16) - to C .
tousefiies showed that the amounts -of ChrYsanthemic-acid
formed by hydrolysis' were qUite small, that three.of the
five majometabolip produts isolated contained the un-
changed moiety of chrysanthemic . acid.in th ester form, and
-thatthe.remaining two major'product also retained the ester .
. linkage. When the latter esters were hydrolyZed and the
Denig test commonly usd as a qualitative test for, chrYsan-
themic . acid.was . apPlied to the hydrolysis Irroducts, the .
'16) tests were positive . Thse results:undoubtedly show that
.the detoxicative metabolim of pyrethroids in insectsdoes
not include the hydrolysis of the ester linkage as its major
metabolism route. . -
-
14
It has been known for some years that addition of
sesame oil to pyrethroids greatly.increases their insecticidal
activities. The causative substance in sesame oil responsible
for the synergic effect was examined, and based on the re'sult
of this study, synthetic synergists such as piperonyl
butoxide and sulfoxide, both of which had a methylene-
dioxyphenyl ring, were discovered. these are serving a
practical purpose. On other synthetic synergist, sesamex
increases the insecticidal effect of pyrethrin-I against
houseflies nine times, and that of cinerin-I twelve times.
As already described in the section on rotenone, 1,3-
benzodioxole, SKF-525A and the related compounds, which
block the activity of miCrosome . OxidaSes, were also reported
to increase the effect'ofpyrethrin against.houseflies and
soldier-bugs.Thee findings of the.sYnergic effects of
various chemical compounds seem to indicate that the meta-
bolism path of pyrethroids in their detxication processes -
is . through the oxidation route rather than the. ester hydrO .-
lysis.
Recently Yamamoto and others19) isolated thirteen
metabolites from 14 0-allethrin and ten from 14 c-PYrethrin-I,
using the oxidase system obtained from abdominal microsomes
of houseflies. The main metabolites were the oxidation product
of the isobutenyl methyl group of the chrysanthemic acid
moiety . of the pyrethroids (Fig.3).
1 7 ,18)
-
1 t Cili C = CR
/ c /C:= 0
0
Correcte4 6x te-* to
CH3 H3
- 1 5 -
c'H3 CH3
C H /
C 1 *1y> c
11 II o
s ee.osom e -FiVADPH -I- Oz.
Chi 3>C HO 0 C
CH3 Ch13
/ H d CHC C / fr( ft
fog"-
o
f-1 CHz-c= CC C fretirolome
if (-films trans 'tram s )**** R C e / e Hz cinerol on e 4441-
ry re tA tin I Rr--->
her i n
Fij. 3 : ajor rnel&bolic route of CA1751Lilfileir) itte
tAe .-transkt.for
..The kn.es-7- -Adits no 5 ijrn flica nce A S 0 ) rela.+1'0-e Comfly ura.hi on of 11-.-1:44-lempt
trot.? I's 'not shown (2) Siet n dardel proC424u.r ', ores - i1 esoro el-km-aeon of
cycj pro pane ckv- bEKy 11 'c a c"fef. tielp R ate re cr-trs 4? 4
* Add eei -t-A e
-
- 16-
At the same time, it was found that the same methyl group
Of 14 -dimethrin and 14 -phthalthrin, which were analogues
of pyrethrin, were also oxidized to the corresponding
carboxyl group. Therefore it is currently assumed that
the metabolisms of all the pyrethroids lidth the chrysanthemic
acid moiety follow the oxidation path as described above.
This assumption is supported by the finding that some .
PYrethroids, namely pyrethrin-II and cinerin-II, which lack
the isobutenyl group, are not synergized by sesamex as
cinerin-I and pyrethrin-I are 20) .
As for the in vivo metaboliem of pyrethroids in
mammals, Miyamoto and others 21) reported on 14 -phthalthrin
(3,4,5,6-tetrahydrophthalimidomethyl chrysanthemate) orally
administered to rats.Phthalthrin was slowly absorbed in
the alimentary canal, and the absorbed material was rapidly
degraded. The main metabolite was 3-hydroxy-cyclohexane-
1.2-dicarboximide produced by hydroxylation of the primary
hydrolysis product.
. . 2.2 Organophosphates* ' ./388 . . .
Parathion appeared on the market at the same' time'-
as DDT did', after the lastwar, and replaced rotenone,.
*Translator's Note: The author uses the term organic-phosphorus- insecticides. The translator uses the term organophosphate as
a generic term to cover all the organic insecticides con-taining phosphorus regardless of the types, that is, phosphate, phosphonate, phosphorothionate, phosphorothiolate etc.
-
.1 7 . -
pyrethrin and nicotine. It showed an excellent insecticidal
effect as a contact chemical. However, since parathion and
other organophosphate insecticides are also highly toxic to
the higher mammals, much time had to be devoted to find
better-qualified, less toxic organophosphate insecticides.
As for their pharmaological studies, the areas examined
in more detail are the action mechanism of the organophos-
phates with relatively low toxicity, the cause of selective
toxicity against insects and mammals, and the mechanism of
resistance induced by the organophosphatef3 among some strains
of insects; these studies have been done quite actively as
a part of basic metabolism study of various living creatures.
Another characteristic point about the organo-phosphate
research to be mentioned here is that, in comparison with
the studies of other insec .ficides, weedkillers.and fungicides,
this was the area in which the application of radioisotope
techniques was carried out since the earliest date of them
all. Indeed it is not going too far to say that most of the
organophosphate action mechanisms were done using the radio-
isotope technique.
2.2.1 Excharige Reactions between S and O.
The main cause of the toxic aCtion of organophosphate
insecticides is believed to be the disruption of nervous
activity caused by inhibition of the function of cholin-
esteras.e. Usually, however, the thiono type insecticides
-
1
18
(P = S) . do not block the cholinesterase activity, .while .
the phosphate ester group (P 0), which can be produced
by in vivo oxidation, show a very strong blocking power.
Therefore, the phosphate ester group is usually considered
to be principally responsible for the acti .iity, and the
in vivo oxidation process is called the activation reaction22) .
The activation enzyme of parathit on to paraoxon is found in
rat liver or Wamon cockroach microsomes, as other drug-
oxidizing enzymes, and it needs NADPH,and oxygen for its
functioning as the activator 23) . The enzyme activity is
inhibited by antiresistant, sesamex, piperonyl butoxide,
sulfoxide, and MGIC-264 23) .
Rats which had been treated orally with dieldrin 24)
' or with chlorcyclizine, phenobarbital, SKP-52511 25) were
shown to have resistance against parathion. The reasen for
this rsistance was proven . to be the increased activity of .
the A-esterase, which was responsible for the hydrolysis
of paraoxon, in their livers and.serum 25) , and the presence
.of another new dtoxication enzyme vas also pointed out 26) .
Nakatsugawa and others 27) studied the metabolism of 35 - S parathion using the rat liver and housefly microsome-NADPH
oxidase system and found- a new type of detoxication reaction
which split the phosphate ester linkage, in addition to the
" . - *Translator's Note: . The author does not - differentiate between '' 'phpi5nate, phospnonate, phesphorothiolat, - and..phosphoramidate', : although:all of them -contain the P . ..group. , -. .
_
;4;
-
,- H
E-e-o
pare( th l'OPI
M e 1 bo A's m (1'
414A 1 . 0k1 4y in l icroSopme
- 19
known activation reaction of parathion to oxon (Fig. 4).
Nea1 28) also obtained the sanie result using 322-parathion.
Furthermore, it is now known that rats pretreated with
barbitals have increased activities in both microsomal
detoxication and activation reaction 25) . By these findings,
ecife-Atiorel., E-L 0 _ 0 0 e z rniavsome 27/.0 Amprtl
Oz
Et 0 > P -OH Ef 0 .
pat-04.0x
de
it is confirmed that both the esterase and the oxidase
participate in the lowering of parathion toxicity after
pretreatment, but which one of the two different enzymes
-
le the more critical for the lowering of the toxicity is
not yet known.
2.2.2 Oxidation of Sulfur
Generally speaking, the insecticides classified
as the penetrating compounds do not loose their activity
even after the compounds remain in the plant tissue for a
considerable period. During this period, the sulfur atoms
often undergo oxidations. One typical thioether, demeton
is a mixture of thiono-type and thiol-type compounds.
(C 2 H 0) P(S)0C H SC H thiono n-type demeto 5 2 2 4 2 5
(C 2H S O) 2P(0)3C 2114 3C 2H5 thiol-type demeton.
The thiono-type compound is oxidized to an oxon type compound,
while the thiol-type compounds tindergo in vivo oxidations to
sulfoxides and sulfones (Pig. 5)29).
-
- 22 -
Fukuto and his coworkers 3(431) examined tlie
metabolism of 32 -demeton in beans and cotton plants and
found that it was converted to oxidation products which
showed considerable cholinesterase blocking.activities,
and they later confirmed the same metabolites were formed
in mammals as well. The first stage metabolites were mainly
sulfoxides, which later were converted to sulfones but this
second stage metabolism was found to be much slower than the
first stage metabolism32) . The thioether groups of 32p-
disyston and 32 -thimet were also oxidized in the plant 29)s
On the other hand, the oxidases that produced sulfoxides
and sulfones were found in mammalian livers and Wamon
cockroach microsomes, and the experiments using 32p-thiometon
showed that they required NADPH and oxygen for their
functioning, and their activities were blocked by SKF-525A
and piperonyl butoxide 33)
(C 2HS O) 2 P (S) S CH2 0112 SC211 5 Dysyston
(C 2H S O) 2 P ,(S) S 011 2 S 2 211 5 I Thimet .
(CHS O) 2 P (5) S CH2 .CH 2 S 02115 ThioMeton
2.2.3 Hydroxylations of Alkyl Side Chains and N-dealkylations
Since 'the early stage of studies on organophosphates,
it has been .known'that schradan (octamethYlpyrophosphoramide)
is *converted to its N-hydroxyme.thyl derivative 34-6)' and
5Wtrerq5eleeMIMMIVe.""
-
-
lately a penetrating insecticide, bidri [3- (di-methoxy-
phosphinyloxy)- N,N-dimethyl-cis-crotonamide] was also shown
to umdergo the same type of metabolism. Two compounds,
N-hydroxymethyl bidrin and N-demethyl bidrin which is known
commonly as azodrin, were isolated from the metabolite '
mixture of 32 -bidrin in rats, insects and cotton plants37) .
MenZer38)' later isolated N-hydroxYlmethyl aZodrin and
. .N-demethyl azOdrin using . bidriii.labeled with 14 0 and 32p ,
, and estimated that N-demethyl compound wathe secondary
metabolite of the. N-hydroxymthyl derivative. It wag quite
.interesting to.know that all these - four compounds had -
significantly.high insecticidal activities against hoUse
.flies (Table 1). This metabolism path was conSidered to be
participated in by an oxidase system, and the insecticidal .
effect against houseflies was greatly increased by addition
39) of the',common synerest, sesamex .
Table 1: Anticholinesterase activities and toxicities of . Bidrin and its derivatives.
CH 30 o H
,CH3O e-ID-C=
" CH 3 . o
Bidrin
Bidrin N-hydroxymethyl Azodrin ,N-hydroxymethyl N-denietliy1
Bidrin Azotlrin . Azodrin
/C1I 3 CH3 ,CH2 .
'Cl-l3
CH 201-i . .
-
24 -
TOCP (tri-O-cresylphosphate) is a very wellknown
synergist for the organophosphates which contain carboxylic
acid ester groups, as found in malathion. TOCP itself,
however, does not have cholinesterase blocking, power, but
when it is activated after being metabolised in a mouse body
or by a slice of its liver, it becomes a strong inhibitor
41) of cholinesterase 40) Eto and hie coworkers isolated a
cyclic phosphate ester, M-1, from rates orally administered
with TOCP, and found that the cyclic ester M-1 had the
cholinesterase blocking power, and proposed the metabolic
path of TOCP as shown in Figure 6. It is apparnt that one
of the ring-substituted methyl group was oxidized by the
oxidase system in the liver microsome, and then the oxidation
product cyclizes, through hydrolysis and intramolecular
rearrangement of the phosphate group, to the final product.
The last stage is probably caused by the action of plasma
albumin. Based on the structure of this active compound,
several active analogues have been synthesized and some
are being used as an insecticide.
2.3 Carbamate Insecticides
Carbamate insecticides generally inhibit the
cholinesterase activity as do the organophosphates. Against
mammals, their toxicities are usually low, and they have
fairly wide selectivities against insecte. being active
against leafhoppers (such as green rice leafhopper)* ,
-
- : - 25
planthoppers (such as smaller brown planthopper, brown
planthopper)*, and aphids (such as corn leaf aphids, green
peach aphid)* but inactive against houseflies and cockroaches.
The cause of these selectivities has been explained as the
difference in detoxication mechanisms rather than the
difference in the cholinesterase blocking power. Although
the pharmacological intrests in the carbamate insecticides
have been found in the same area where they were found in
organophosphates, since they have a wlder margin of selectivi-
ties, more metabolism studies specific to each insect are
. desirable.
The metabolism of the carbamate insecticides varies
depending on the subjects of study, mammals, i'nsects or
plants, but it is classified into the following three major
areas; (1) hydrolysis of carbamate ester group, (2) oxidations
(hydroxylations of ring and ring substituents, N-demethylation,
and N-hydroxymethylation of corresponding N-methyl groups),
and (3) s complex formations such as glucuronide formation,
glycidation, sulfonation or glycosidatione when metabolized
in plants, of the hydroxyl grouppand.carboxyl groups produced.
by the .aforementioned processes.
Only 1-naphthol was the isolable metabolite of
14 -carbaryl which was a representative carbamate insecticide 42)
*Transl.'Note: Added by the translator as these were the ones found in Japan. . , .
-
C11 3 0 8
0P-0
C11 3
NADPI1,0,
1-.yd r.oxy:r. e TOCP (9000) .
O
0 P 0 -
o
plasma album%
C113 0
0 P- /
11- 1 : ( 1. 2 X 10' )
- 26 -
Fig. 6 : Metabolism of TOCP 'Figure in ( ) is /390 relative anticholinesterase activity]
TOCP
( 1 )
at the early stage of metabolism study. However,Dorough
4 and others 3) later isolated several compounds shown in
Figure 7 from the metabolite mixture of carbaryl which was
labeled with 14 at naphthyl,,carbonyl and -methyl after
treating with a liver-microsomal NADPH oxidase system:. They
also isolated 1-naphthol which was -the hydrolysis product
and its derivative using liver homogenate. Recently, in
addition to the metabolism requence shown in the figure,
0-dealkylation, hydroxylation of ring substituents, and
-
kti,o1
creme
OH
0 it
0 dSHMe wt icrosome ' P H
02_
vAecrosome
NADPH 02. je
o L 141-1cFl 1oji
Sle o It " oixM . octsli-Me_
erect* r kyetrot-y
Cae 60..ry OfKict
OC (Me
27 -
Litre r mecros omai oix.:culobi of
Carbe. ry I iv% s ech'c i'de e v% t- o)
-
-.28 -
sulfoxidation were reported using thirt y. three different,
methyl and dimethyl carbamates which were labeled with
44) . 14 0 . Among these newly found metabolites, some were
even stronger cholinesterase inhibitors than the original
44) carbamates . Although the activity of the oxidase which
transformed carbamates into metabolites was inhibited by
piperonyl butoxide 45) , the oxidase itself was found, by an
in vivo experiment, to be-synergistic* just as sesamex was45-48)
Four glucuronides (shown above.) and sulfate esters
of the oxidation and hydrolysis products:were found as the
products of in vivo metabolism of carbaryl. labeled with .
methyl-14 0., carbohyl-I4 0 and naphthy1140 in rats and : guinea
pigs49) . In th metabolism of this compound, since a
rl.atively large amount of th baterial was not hydrolyzed,
the metabolic pathways were mainly xidations and derivative
formations. Two compounds, 1-naphthyl methylimidocarbonate
0-glucuronide, which is the direct derivative, and 4 -
(methylcarbamoyloxy)-lnaphthyl glucuronide were the major
metabo 1 ites 49) . The same metabolites were'foilnd in experiMent
using pigs, mnkeys and sheep 5) . libWeVer,..in the case of
14 0-3,4-dichlorobenzyl N-methylcarbamate, its hydrolysis
was the major mtabolic'rute at the initial stage, which
was followed by oxidation'to yield the corresponding
carboxyluc acid, wilich was . isOlated, and.which,' in turn,'
*Transi. Note: synergistic to the action of the carbamate , itself?
-
O Gr
0 Cq rrOz., Or
-v1,041.4-6 le 4 e.
VIA 0%10 r vA 0:410tek
ro n e
- 29-
0 CI- ' dzrzl Me
was converted to and isolated as the amide of glycine,
namely, 3,4-dichlorohippuric acid 51) . Metabolism studies
of penetrating carbamate insecticide, bano1-14 0 (2-chloro-
4,5-xyly1 methylcarbamate), and carbaryl-14 c were conducted
using bean plants. The major metabolites were found to be
their N-methyl derivatives 52) 0r glycosides of their aromatic
53,54) ring hydroxylation products
Another penetrating carbamate furadan (2,2-dimethy1-
2,3-dihydrobenzofurany1-7N-methyl carbamate)'was studied
using cotton plants, corn plants, houseflies, larvae of
salt marsh caterpillar and mice, and its metabolic pathways
in different species of plants. insects and'animals were
compared using 14 c and 3H markers. As shown in Figure 8, the
major paths of the.metabolism were essentially the same. /391
Namely, furadan was first hydroxylated to 3-hydroxy furadan,
of which the hydroxyl group was difficult to react . to produce
a derivative, and then the large portion of 3-hydroxy furadan
was oxidized to 3-keto furadan, which was hydrolyzed to give
-
- 30 -
'Me. oxid ox:d .
O=C N Me.
o 0 N ctizoH
o 0=e ts1 Me
'Me Fi
Fikrad an
0 H
COM
4-or-ma-Won.
e+0,1 s -re .0+ e u-, vn cretti-Wre s
f' . ylkyvt- s eYS e c..4- s
. 0
}10.
'
c l CI
3,4-clich1o"ro- henzyl N-methyl carhamate
0
CI l
3,4-dichloro-' hippuric acid
-
- 31 -
the corresponding phenol. The phenol produced various /391
derivatives 54) .
As for the selectivity of carbamatesi a few probable
causes for it have been cleared mainly based on their meta- 1
bolism studies. Namely, the susceptibility of honeybees was
estimated to be due to their relatively low oxidase potency 55,56)
The carvamates with low toxicities against mammals generally
were also easily detoxucgted and quickly excreted. On the
other hand, highly toxic carbamates such as furadan and temik
D-methy1-2-(methylthio) propionaldehyde 0-(methyl carbamoyl)
oximej were found to yield metabolites which also had the
same type of toxicities, and therefore in these carbamates
the in vivo metabolism is more likely of a nature of
activation of toxicity rather than detoxication56 ' 57) .
2.4 Organochloro Insecticides
Organochloro insecticides which include DDT, MO,
cyclodiene compounds and others, generally have small acute
toXicities against mammals but their insecticidal activities
are quite strong, and their residual insecticidal activities
are also high. The machanism of th insecticidal activities
has not been established. Since this group of insecticides
has been used since very soon after the war, appearance of
a large number of resistant strains of insects has been
recorded. The radoiseope technique has been frequently
applied to the exploration of the mechanism of the r sistance
formation.
;-,:;1
V,, b1
-
Generally speaking, the organochloro insecticides are
stable and difficult to decompose even in plants, soil '
and water, and they remain, without decomposition, for a
long period. Consequently, the chain of food intake and
excretion cycles tends to result in their eventual cumulation'
in vertebrates at high concentrations. The isotope technique
is therefore being used in the study of the metabolism of
these chloro compounds in mammalians.
Three major types of reactions, namely dehydro-
chlorination, oxidation, and reductive dechlorination, are
known as the metabolic routes of DDT (Fig. 9). Among thes
pathways, the dehydrochlorination of DDT to DDE is the
critical factor to determine the DDT resistance of house-
flies 58,59) .
As for the oxidation pathway, kelthane from the
Kiiroshojo-fly * was the first isolated metabolite 6) . Later
kelthane or kelthane-like substances were isolated from the
housefly, Chyabane-cockroach ** , and Sashi-game***, when
labeled DDT was used 61,62) . The oxidases of-these insects
had the same characteristics as those of mammalian liver
microsomal oxidase, requiring NADPH and oxigen to oxidize ++61). DDT and their activities being accelerated by Mg 6l
Note: domestic fruit fly, Drosophila melanogaster.
" Literally brown-wing-cockroach. The reference (61) shows German cockroach.
*** II " Sashi-tortoise. It must be an insect.
-
- 33 -
t.
OH FJ
0:5Cl.? CL.C. CL
,of f kel 4-tuule.
H Ct. j>--C N
Cl
DT
b.(11/ 7# (p)Ci!- C
it
D D E ce>'d
rm'cr- osome , WAD I) Oz
ID P
eat) oks (Y.'s ot DDT
tcLt- f (4) - CLC., CL CLC CL
CL
kyietro4(.314*e
iDD T
Y (oc,L4- c - ? c ter oH
The enzyme activities were foUnd to be particularlY good
ing)arathion-resistant.houseflis 61) . The larvae of '
Sashi-gam were quite strongly DDT resistant, and the
, larvae treated with.SKF7525A increased the-effect of DDT,
and the yield of kelthane-like material in -their bodies
decreased. On the other:hand, 5-methylchlanthrene lowered
the effect of DDT", and the bodily content of the hydroxylated
.substance increased. Therefore.it is quite sound to
conclude that the MicrosOmal oxidative . mtabolism. vas ,
63) te cause of the DDTresistance ,
-
Chlordane, heptachlor, aldrin, isoaldrin, dieldrin
and endrin are all highly chlorinated hydrocarbons and they
are synthesized by diene condensations. The first four of
the afore-listed insecticides are epoxidized in the body,
and the epoxides are physiologically active and are chemically
stable compounds. Epoxidation is quite well-known in insecte,
in addition to the same found in mammals64 e 65) . Namely, the
formation of heptachlor epoxide from 14c-heptach1or66) , and
the epoxidation of aldrin to dieldrin and that of isodrin
to endrin 67) are some - of the-well-known examples. The
symptoms of poisoning by these chemical insecticide
in insects are parallel to the progressing of the epoxidat1ons 67) ,
and, in order to cause the poisoning symptoms supply of
oxygen is needed 67) . Sesamex, which is a common synergist,
decreases the activities of aldrin and heptachlor against
houseflies and this has been explained as due to the inhibition
of epoxidation of these chemical s68) . Ail these results con-
firmed by in vivo experiments clearly indicate that the
metabolism mechanisms of these are deeply related to the
reaction mechanism of microsomal oxidase.
Liver microsomal enzymes of rabbits and rate epoxidize
heptachlor 69) , aldrin69) and isodrin70) . and the enzymes
require NADPH and oxygen for the readtion and their potencies
53)* are lowered by SKF-525A, piperonyl butoxide and parathion
Tranel. Note: 58) ?
observed
-
CI
CI '011.
ilydroxychlordene
Cl
Cl
Chlordene epoxide
*Transl. Note: 74) cannot be found.
() 11
II
35
In the case of insect e , the epoxidations are reportedly
71) carried out by cockroach fat-body microsomes and the
71- ) 'housefly abdominal microsomes 73 /392
. Dieldrin which is the product of epoxidgtion of .
14 0 -aldrin waa further tranformed to highlY polar . trans-.
6,7 7dihydroxy7dihydro , aldrin (aldrin glycol) by.the expoxide-. 75-78)! ring opening reaction, in - insects and in mammals
(Fig. 10). The physiological actiVity of this compound
against insects is approximately. one twelfth. of that of
77): dieldrin ,. and the enzyme repponsible for the epoxide
opening was found in livr microsOmes of'housflies and
mamMais 79)
Fig. 10: Metabolisms of aldrin and dieldrin (in vivo, in vitro)
ci 1.1 . n o
to-
atNI a cl . cI Aldrin Die Idrin glycol
In the case of diene compounds, in addition to the
epoxidations by the microsomal oxidase system, hydroxylations
have been recently reported. For instance > 14 -chlordene
yields epoxy compound and hydroxychlordene which is not .
63) (or 68?) toxic
'
-
This hydroxylative detoxication of chlordene is
carried out by an enzyme whose functioning mechanism was 80) 'verified in part by in vivo synergistic effect by sesamex
2.5 Inductive Activation of Drug-oxidizing Enzymes bY
Organochloro Insecticides
Consecutive administration of barbituric acid to
mammals, and the resulting drug-resistancy have been studied
quite well. The mechanism of resistance to barbituric acid
was explained as the result of increased liver microsomal
81) capability to hydroxylate barbituric acid . If liver-
carcinogenic 3'-methy1-4-dimethylaminoazobenzene is
administered .together with 3-methylcholanthrene, the ' 82) former's carcinogenic actiVity is entirely suPpressed.
and this is now known as a result.of.ah increased activity
level of the micrOsomal oxidase, which . became capable of .
converting the carcinogen into non-carcinogenic substances. . . .
.The number of these componds, Which are able to increase.
the drug-metabOlism activity.of liVer microsomes, as shomin
by barbituric acid and 3-methylchlanthrene,: is increasing.
recently, akd this phenomenon ia called induction of drug-
metabolizing' enzymes by drugs, and.those. drugs which increase
the activities of enzymes are called.enzyme Inducers 83)
Intensified Potency of microsomal oxidase by insecticides
has also been found in numerous.cas. The*.first insecticide
84 .1 85) Shown to be an inducer was chlordane 1 and besides._14at,
-
.Chlordane .
Methoxychlor
DDT -;
DDE
DDD Kelthane
Endrin
Dieldrin
Aidrin
*Heptachlor
Heptachlor epoxide
BHC
37
various other chloro insecticides shown in Table 2 were
proven to be induce rs86) . The same effect of induction
was a],so confirmed in DDE, whicii was a non-toxic metabolite
of DDT.
Table 2: Organochloro insecticides that promote metabolism of drugs. .
As one 'of the in vivo functionings of the micro-
somal enzymes, its relation to steroid metabolism in
mammals has been clarified. Further, the relationship
between the steroidal metabolism and the drug-induced
activity of the oxydase system has been reported by conney 87)
He found that, elen phenobarbital was administered to rats,
their, liver microsomal potency to hydroxylate steroid rings
of testosterone and androstenedione increased drastically.
It is indeed exiting to find that the hydroxylations of
steroid hormones by liver microsomes can be subjected to
the same effect as the drug-metabolizing enzymes are. It
is therefore important to investigate how various drugs
that influence the activities drug-metabolizing enzymes
ultimately effect the general physiological system of bodies
through the changes of steroid hormone metabolism. '
-
- 38 -
The effect of organochloro insedticides on the
steroid metabolism is becomming somewhat clearer88) , and
currently it is estimated 89) that the rapid decrease of
the feathered tribe in Europe and in North America might
have been caused by the imbalance of pex hormones owing to
the chloro insecticides which generally show high residue
rates. For example, pigeons treated with either DDT or
dieldrin or both showed higher contents of polar metabolites
of 14 progesterone and 14 testosterone due to the increased /393
activities of their liver microsomeNADpH oxidase, and the
metabolites after treatment with DDT as well as with diel-
drin were found to be different (Fig. 11).
Fi. 11: Chromatography of Testosterone metabolites in pigeon liver as induced by chloroinsecticides.
-- DDT *-G- Die!chin
DDT+ Dieldr.IN Compel
distande'Of Moving (col) .
On the other hand, the livers of untreated control pigeons
did not indicate the presence of these highly polar
metaboiites. The results undoubtely suggest that there
-
- 39 -
. is always a possibility of drug-induced imbalance. of . sex
hormones, and this is the basis for the speculation 'of the
decrease,of birds'owing io their poor reproducton89) . As
quite a' lot of reports 'are. prePared regarding:the. '
induction of insecticides, more effort should be.devoted
to clearing the.possible inhibition of reproduction bY . various
other pesticides as well as their metabolites.
3. WEEDKILLERS
.In the sections on insecticides the author described- .
their metabolic patterns,forcussing hie attention on the
oxidative metabolism in mammals,.insects and plants, and
.discussed the width of the seleptivities of insecticides.
In the field of weedkillers, the - selective ssceptibilities'
'of plants to chemical substances and the caue. of the
selectivities are alsO most important subjects. As expected,'
we find a rather large number of examples of application Of
radioisotopes especially' in the studies of the absorption:
mechanism- of the plants, the . mobility Of chemicals in the
plants-, and their metabolic pathway. In addition to these
examples, since most weedkillers are applied.to the soil,
the stability, -Mobility and availability of weedkillers in
the . soil; their degradation in the soil, and their metabolism
re.soil bacteria are important problems. Therefore, we see
a considerable number of research reports in these areas as
well.
-
- 40 -
H "...N./H (Cill') (C3111)
H 1-4C3
3.1 Trifluralin
Trifluralin(040t-trifluoro-2,6-dinitro-N,N-
dinormalpropyl-p-toluidine) is a toluidine-type weedkiller,
and is commonly used to destroy weeds of the rice-plant
family and other common wide-leaf weeds. The degradation
of'14 -labeled trifluralin is different depending.on whether
the conditions are aerbic or unaerobic..NaMely aerobically,
dealkyIation'is the first Step of.degradation in the soil,
which is then follOwed.by reduction of the nitro group, but
reduction before dealkylation is the first step of anaerobic
) clegradation9 . The plants which show resistance . agaihst this
.0,N NO, , 0,N f'. 1 NO3 03N e).1 NH,
CF, Trifturalin
CF, .CF, 6.q.7
decdkyi I no e ci eri ect ve
chemical were found to be poor absorbers of the chemical
from the soil90) , and the major metabolities in carrots
were found to be the dealjyl compounds 91)
3.2 Di phe nami de
This acid amide type weedkiller has high mobility
in sOil, and is an excellent weedkiller for weeds of the
rice-plant family and annual wide-leaf weeds. The Metabolism
studY Using a 14 c-labeled marker in plants shoWed that
-
- 41 -
demethyl compound (N-methy1-2,2-diphenyl acetamide) was
. the major metabolite, and the yield of thi conversion
96)*' was extremely high . On the other hand, when the same
. marker was administered to rats, N-demethyl compoune),
N-hydroxymethyl compound(s) and their derivatives, 0- and
N-glucuronides, and 0-sulfate were isolated from the urine,
indicating that the transformation of the N-methyl group s
was the major metabolic pathway and the other possible route,
that is, hydroxylation in the aromatic ring, was almost
negligible.
Diplienzu.nid
3.3 Diuron and Monuron
Both diuron D-(3,4 7 dichloropheny1)1,1dimethyl
urea3 and'monuron D r-(p-chloropheny1)-1,1-diMethyl urea]
re phenyl urea-type weedkillers: They are absorbed by the
roots and accumulated in the leaVes and inbibit the Plants'
photosynthesis. All the weedkillers which have the -NH-00-
group, namely,'carbamate-type, urea-type, triaZine-type and
anilide-type weed-killers, block the Photosynthesis, and
it.is assumed that the' hydrogen bridge formation between
*Translator's Note: 92)-95) are in section 3.8
-
this atomic group of the weedkillers and the free imino
group, hydroxyl group and the carbonyl group of the
chlorophyl-protein complex in the plant leaves is the cause
of clocking photosynthesis.
Resistance and susceptibility of a few plants against
diuron and monuron were examined using radioisotopes. There
was no difference in the mode of absorption or moving and
distribution in the plants between the cotton-plant, which
was relatively resistant to these chemicals, and the bean
plant, which was susceptible to theme Although both mono-
demethyl derivative.and di-demethyl derivative, which* were
toxic to plants, were commonly isolated as the metabolites
(of diuron) **' *** , the toxic demethyi derivative(s) could
not be found in the metabolites from the cotton . plant.
Similar demethyl derivative(s) were isolated as the metabolites
of monuron. Therefore, the selectivity difference between
these plants against these chemicals was considered due to
the quantitative difference in detoxicative metabolism 97) .
Recently it was reported that an oxidase in cotton leaves
oxidatively removed the methyl group(s) of 14 -monuron to
produce N-demethyl derivative(s) 98) . This enzyme was found
in microsome fraction as the sametype of enzyme did in
mammals and insects, and it required NADPH and oxygen to
*Transl. Note: either one or both? ** " tt added by the translator
from which plants?
-
do the job. This was : the -first : .exaMpl of cxidation.of
pesticides by a plant oxidase and therefore it
noteworthy.
0 CI ,_=,) C2N a "i5 < CH' 11 e C711,
011, N.-- Cit
Neron
o ' r Nm7.!:
-
- 44 -
99) susceptible or resistant . When 14 -dicamba Was administered
to rats, most , of the drug was excreted in the mine, and about
1/5 of it was a glucuronide drivative and the other major
portion was unchanged dicambalW)
C001-1
. M crrlba.
3,5 Paraquat, Diquat
Both paraquat (1,1=dimethy1-4,4=bipyridinum salt)
and diquat (6,7-ehydrodipyrido pyrazinum
salt) appear to block the photosynthesis of plants. Since
they are quickly deactivated in soil, they are usually applied.
directly on leaved and stems. Both 14 0-paraquat and diquat
are relatively stable in plants, and are only difficultly
metabolized 101) , but they are quite susceptible to soil-
microbial decomposition. Microbes first demethylate paraquat
to 1-methy1-4,4' -dipyridinium ion in which the two htero-
aromatic rings are oxidatively cleared to yield 1-methyl-
4-carboxypyridinium ion. This sequence is entirely different
from the photodegradative reaction, in which the formation
of 1-methy1-4-carboxypyridinium takes'place (immediately)*
after the first step of the degradation, i.e. splitting of
the hetero ring (instead of de-N-methylation) .
*Transl. Note: added by the translator.
1
* 10 2 , 1 0 3 )
-
1 -methyl -4 -carboxy-: pyridinium ion '
3.6 Simazine, Atrazine
+ -
(C11 3 - br)CNr C11 3 CI 13 N1-
. .
Paraquat 1 -methyl- 4,4'- dipyridinium ion
-4
Triazine-type weedkillers cannot'sterilize - the
Weedss : seed,' and their reation mechanism is estimated
to,be identical With that-of .urea-type naMely,
they are absorbed by the rots and cumulate in the leaves,
where theublock the plants' photosynthesis by. hydrogen:bond
formation with the chlOrophyl-protein.cOmplex that.is
critically important for the:photosynthesis. Bth simazine
C,2-chloro 74,6-bis(ethylimino)-s-triazinelandiatrazine
C2-chlor6-4-thylimino-6-isopropylmino .-s-triaiine3 have
strikingly slective actractives against ,corn plantS and
'againbt weeds. The metabolism of simazine was examined by
applying labeled simazine to the. resistant.corn plant, and
it was learned that the detoxication by the plant was mainly ,
caused by the plant's ability to substitute the chlorine atom
with a hydroxyl group. This non-harmful hydroxy simazine
was actually synthesized non-enzymatically by a reaction .
of benzoxazinone (2,4-dihydroxy-3-keto-7-methoxy-1,4-
benzoxazine) which was found in the plant. The concentration
of this latter compound in a plant and the drug resistance
-
CI
C
C3 H8SH-C C- NHC,H . N o
Simazine OH
Ces - NH-C-C-NHC11 ,,
>se- .
1-Iydroxy Si 'mazine
a
N/S.,..N
(C1:13)MCON-C u4114C,I1, N O
Atrazine
ci
II C;HeNII-C,...,; .A1.. NH.
Simazineffixl-Jkft:YdeethY1 derivative
- 46 -
of
the plant was repOrted tobe very closely.corrlate 104-106).
However, there has been tarepoi-'t(s) t -o debate the relation-
.
Another metabolic route of triazine chemicals in
plants is dealkylation. Shimabukuro studied the metabolism
of 14 -atrazine in bean, and found 2-chloro-4-amino-6- C
isopropylamino-s-triazine, which was.the principal metabolite,
but no hydroxy triazine derivative 107,108). This deethyl
compound was also active in the inhibition of photo-
synthesis although its activity was lower than that of
atrazine itself. Bean plants are not as strongly resistant
/395 to atrazine as corn plants are, but are more strongly
resistant than oat. Therefore it was estimated that.the
plants which were moderately resistant to triazine-type
weedkillers might be detoxicating atrazine by deethylating
some portion of the absorbed atrazine 108). It was also
confirmed that the triazine-type weedkillers were hydro-
10)* xylated in sciil 7 , and a soil microbe, Aspergillus
* Transl.Note: Misprint of 109)?
-
3.7 Propanil
- 47 -
fumigatus converted 14 0 -
simazine to 2-ch1oro-4-amino-6-
ethylamino - s-triazine by deethylation as bean dis ilo)
An anilide, propanil (3i4-dichloroproPion'anilide)
is a contact-type weedkiller, and it seIeCtively destroys.
annual weeds such as barnyard'grass, mehishiba* and other
weeds of the rice-plant family,. lthYough it hardly.damagee.
'rice:plants. The mechanis .mHof the 'selectivity of this weed
killer was studied in.detail and the results shoWed that
the differnt activities against'rice.plant.and barnyard
gras.s were not caused by the.difference in absorption and ,
- mobility in these two plants but:by:the degree of the
detxication reaction,.which wasthe hydrolyis of.propanil-
.111 to 3,4-dichloroaniline (DCA)and propionic aci -114)d .
It was fOund that. rice plant at its third-leafing.,age .
had 26 times as large a detoxication activity as that of
barnyard grass113) . The enzyme which decomposes propanil
in rice plants was studied by Freer and others115) . It is
also known that the organophosphates and carbamate insecti-
cides'blocked the activity of this enzyme, and this finding
can explain why the mixture spraying of this weedkiller
and organophosphates or carbamate insecticides caused the
116)115 112 ill effect on the sprayed rice plants '
.* Transi. Note: water-chestnut?'
-
15 1-I-C-CH .(0111C11., - I
NH C-C,113
48
' CI - r"c y".CI Cl CI CI
Propanil DCA DLA . . . .
Recently. Yih and otherS 117) proposed . a different
Mechanism'.of prOpanil metabolism after analyzing the -
metabolites obtained. from carbonyl and ring labeled propanil.
TheY suggested that the first step of the degrdative meta-'
bolism was the oxidation to.3,4-dichlorolactanilide '(DLA)
which was then hydrolyzed to.DCA and lactio - acid rther . than
to propionic acid, While the older mechanism assumed th
direct hydrolysis of the anilide linkage to yield DCA . and
proPionic.aCid.
The fata of 14 -43CA prodUced in rice:plants after
degradation of propanil has been the .subjectof many studies.
Sti i 1 118) discoVered four DCA derivatives, one-of which. was
N-. (3,4-dighloropheny1)-gluccisamine. ih 119)* clarified that
other.DCA , derivatives were a mixture ofiDCA - glycosides-of
glucose, xylose and fructose and other unidentified DCA
glycosides. However,.the .content of these Water-soluble
DCAcarbohydrte coMpounds was rather small and a major
portion of the DCA derivativesSfas .the complex compounds -
of DCA and lignin cellulose, hemicellulose and other high
->Trnsl. Note.: addect.by the translator.,
-
molecular weight cll comPonent. The change Of the side
chain propionat of 'propanil was eXamined Using a:marker .
qabeled at its terminal methyl group and at the Carbonyl.
.It was Confirmed . that a large portion of the propionate ,
group became 14 2 before being absorbed. by the plants. CO'
This was explained by the rapid . hydrolysis of the propionate
amide group.to propionic acid, which underwent P-oxidation t
produce CO2 120)
Since propanil decomposes quickly in soil and is
deactivated, the weeding effect by the soil-treatment method
was said to be very poor. This rapid dcomposition was found
to be due to the hydrolysis of propanil to DCA by soil
bacteria121,122). Acylamidase which exists in mammalian
livers was also known to decompose propanil l23).
3.8 Naphthaleneacetic Acid
The wellknOwn plant hrmone substance, 1-naphthalene-
acetic acid is metabolized to itsderivatives in plants. Th
major metabolites isolated were aspartic acid . amid
EN-(1-naphthalene acetY1) aspartic acid] and "a glucoside
(0-naphthalene actyl glucose). An oxidation product,
8-hydroxy-l-haphthalene acetic acid and its. glucoside . were
also identified92 ' 95) .'The distributions of these metabolites.
were examined using 14 0-market compound, but they were quite
different depending on the plants examined94) , On the other
hand, most of the labeled compound was excreted in urine
-
DCooH it I C ii
C .00H
H2 CO 0 H
I v)alelni-kale me,
l lAkco s ct e, 31-y c e ae-ritrcx-Wve,
szx.s rem-11 % c c . 4 ctg r mkt' (re.
ti
CC-Hz 0 im.e09'1 CH.4HC.CO0H, 0*
when administered to rats, and the glycine derivative
(naphthaceturic acid) and the corresponding glucuronide'
95) were the major metabolites .
4. FUNGICIDES
The number of .examples of application of radio-
isotopes in the field of biochemistry of flIngicide was
relatively small, in comparison to thosein insecticides
and weedkillers.-The reaSon for this is found in the facts
that most of the reaction mechanism - of the.fungicides Was
solved without using radioisotopes, that, although in'the
application of insectiClidesi numerous.problems Such as ,
comparative toxiciV:studies between higher-vertebrates
-
and insects, selective toxicities among the insects, and
the mechanism of resistance, and also in the field of weed-
killers, the problems of selective toxicities among plants
were solved mainly with radioisotope techniques, the same
types of studies were not very important when application
of fungicides was studied, and that actually most of these
problems were solved without the aid of the radioisotope
technique. However, in recent years, a large number of new
fungicides have been developed and are being used or about
to be used. Naturally more knowledge about the mechanisms
of the action of fungibides, of metabolism and resistance
of fungicides and further data on the metabolism in higher
plants and animals are needed, and the studies using isotopes
4) are rapidly increasing. Since Kuwasaki 12 already reviewed
the general application of radioisotopes in the studies of
fungicides, this author discusses only those newer fungi-
cides, namely, organochloro fungicides and organophosphates,
reported after Kuwasaki's review..
PCBA (Pentachlorobenzyl alcohol) is,a well-known
fungicide to protect rice plants from rice withering disease.
It does not have fungicidal activity against the fungi -
responsible for the disease when they are placed in a test
tube or on rice plant leaves but it prevents rdce plants
from contracting the disease. However, only little was
known about the 'mechanism of its functioning. In order to
-
clum cil
ci ci ci
ci -Vji ci ci ' ciVci
CI . , ci CI
PC IA PentacIdire- Pentachloro-
benzylatdekde . benzoic acid .s%
O0 11 .
52.-
clarify the action mechanism 'or the toxicity of PCBA, its
metabolisms in fungi, plants and animals were studied.
When rice plants were treated with' 14 c-PCBA, there was
little radioactivity in the aqueous extract, but the ether-
soluble part contained unchanged PCBA and two unidentified
125) . . 126) metabolites . Kakinoki and other detected pentachloro-
benzaldehyde and pentachlorobenzoic acid from rice plants
treated with PCBA, ,and they estimated that oxidations of
the side chain were the major metabolic route- On the other
hand, when 14 0-PCBA was orally administered to rats, only a
small amount of the chemical was absorbed and found in blood,
liver and urine, but the major portion was excreted in the
feces with no change in its structure. The metabolites
found in the urine were pentachlorobenzoic acid and PCBA
glucuronide 127) .
In order to clarify the action mechanism of a similar
organochloro fungicide, PCPA (pentachlorophenyl acetate),
absorption and transformation of the14 c-labeled fungicide
in the pathogenic fungi of rice withering disease and in
rice plants were studied. In both fungi and plants, the
absorbed PCPA was hydrolyzed to pentachlorophenol (PCP).
-
Therefre the fungicidal - actiVity of PCPA was probably
cased by ita metabdIic PCP128) cased'by ita metabdIic PCP
EDDP (0-ethyl S,S-diphenyl phosphorodithiolate)
is an organophosphate type fungicide and it shows either
curative or preventive effect on rice withering disease. The
mechanism of action has not yet been clarified. Uesugi 129)
reported on its metabolism in the pathogenic fungus of the
disease. 1%me1y 32p-EDDP was quickly.absorbed into the fungi
and hydrolyzed to inorganic phosphoric acid via 0-ethyl
S-phenyl thiophosphoric acid and ethyl phosphoric acid.
At the initial stage of this metabolic pathway, an inter-
mediate metabolite, which was soluble in toluene and was
fungicidally active, was detected. There was no difference
in the metabolic patterns of EDDP by susceptible fungua and
resistant fungus.
As to its metabolism in plants 130) , was rapidly
subjected to hydrolysis, and its initial metabolites were
0-ethy1 S-phenyl thiophosphoric acid (dephenyl derivative)
and S,S-diphenyl dithiophosphoric acid (deethyl derivative)
and later as the metabolism progressed, 0-ethyl phosphoric
acid ana phosphoric acid increased in the'metaibolite mixture.
-
o
7 e.
dphenyl derivative
0 sO
.EDDP
'deethyl derivative
-- 54 -
It is reasonable to assume that the degradation of EDDP
in rice plants took place in the order of the intermediate
compounds listed above.
1) Fukami and others13 compared the metabolism
pattern of 32p-EDDP in various microbes and animals, namely,
Bacillus subtilus, Fusarium, rice withering disease fungus,
cockroach and rat. The patterns Of metabolites found in
water-soluble and chloroform-soluble fractions obtained
from each species were nearlY identical. The 32p-EDDP Orally
administered . to rats was almost exclusively excreted in the
urine, nd watrsoluble metaboiite in the rats' tissue and
urine were the cam as'found in rice . plants. In the 'case of
,cogkroaches, the results were "again the same...SeruM,.liyer
microsome, supernatant Of liver and other tissues of rats
contained enzymes whiCh'hydrolyze EDDP,'and these enzymes .
appeared to participat.in ihe metabolism .of EDDP. Un th
other hand, body tissues of rats and cOckroaches, and their.
exCrements Contained some in viv: .metabolites which .Wer
soluble in chlorciforM and which were not the nyrolysis
_
-
7?
- 55 -
products described above. Since these unidentified metabolites
appearedto Widentical with the oxidative metabolites of
EDDP with the NADPH-oxidase system obtained from the.liver
and fat-body microsomes of rats and cockroaches, they'were
considered to be ring hydroxylation products. Further these
substances were identified from the metabolites of rice
withering disease fungi, after treatment with EDDP, although
they were not found in the metabolites of EDDP-treated
Fusarium and Bacillus microbes. They are currently estimated
to be the same toluene-soluble materials isolated by Uesugi
and others, as described above.
IBP (0,0-diisopropy1 S-behzyl phosphorothiolate)
is also an effective fungicide against rice withering
disease and it is an organophosphate type chemical. Its
metabolism in the pathogenic fungi of rice withering disease
was examined using a 35 s and 32p doubly labeled IBP. IBP
was taken - in very rapidly, and its major portion was hydro-
lyzed to 0,0-diisopropyl thiophosphoric acid. As the
metabolites other than the hydrolysis product(s), two
toluene-soluble intermediate metabolites were found. There
was no difference in the patterns of metabolism between
the IBP-Susceptible and IBP resistant-fungi l .
0 . 3>
CI-10) e-S-CH;Ct I-1, 0H3 t .
.
IBP , .
L. ,
-
56: -
'
5. SELECTIVE TOXICITY-
In order to clarify the cause of the . seledtive
toxicity of pesticides, it is important to examine every
step , of the interactions between the pesticides and the
substrates, plants or animals, until their pharmacological
activities'are revealed by the symptoms of the substrates,
and how the difference of the chemical structures of the
pesticides and the difference of the substrates are reflected
in the interaction of the chemical and the substrate must
be analyzed at each step, physicb-chemically and biochemically.
As factors in the selectivities of chemicals may be counted
the absorption of the chemical, its mobility , and distribution
in the body, its routes of metabolism and the mechanism, and
further the sites of action of the chemicals. In this review,
the author so far has explained the width of selectivity
of insecticides, weedkillers and fungicides individually.
In the following sections, the author attempts to describe
the selectivities of a few insecticides, of which the
principal cause of the seledtive pharmacological action
was undoubtedly shown to be either oxidation or metabolism
through complex formations.
5.1 Seiective Toxicity of Rotenone
Rotenone is' a selective insecticide. Its site 's of
action are in the electron transfer system in the respiration
process of insecte as are its sites of action in mammals.
-
57
As already described, the mtabolites of 14 0-rotenone by
the microsomal system of mammals or insects are almost
exclusively hydroxylated compounds, and the metabolites
formed were essentially the same regardless of the sub- -, 10) . 0) estima strates' - ' 9; Fukami and others 1 9 ' ted that
there were three factors participating in the selectivity
of rotenone against insects and mammals.
The first factor is the quantitative difference of
detoxicative activities by oxidations. 14 c-Rotenone is
oxidized stepwise to various hydroxylated derivatives
which are less toxic than rotenone, by microsomes of various
living creatures. his activity of detoxication is the
strongest in rat liver; the cockroach fat-body has a weaker
activity than the aforementioned and the middle intestine
of cockroaches has an even' weaker activity (Table 3).
Comparison of the contents of P-450, which is a component
of microsomal oxidase systems, reveals that, in cockroach
fat-body, it is less than 1/7 of that in rat liver microsomes.
This low relative content alone indicates that the activitY
of detoxicative metabolism of rotenone in cockroach must
be very low'.
-
Ether layer 4 1 c (%'
15 13 ' 31
'cockroach fat body
1 1
cockroach middle intestine 63 24, 10
61 . 24.
rat liver 63 15 .
cockroach middle intestine
1 1.
- 58 -
. . . . .. , . . . . . .. .Table-3:- letabolism of . rotnone'by cOmbined.micrdsomes . . .
Or microSoMe sUPernatants Of.inseCts or 'animais . .
Combination
Mcrosome suiDernatant rotenone rotenone hyroxylated . mtabolites
Aqueous layer 0 '(%). .
rat liver
rat liver rat liver 76
cockroach fat body
68 .16
18
-
-59
The second factor is sthe difference in the activities
of secondary reactions by supernatant enzymes of various
tissues and organs of the insecte and animals. Although the
hydroxylated metabolites of rotenone have only low pharma-
cological activities, they are still toxic. These metabolites,
however, can be converted to either insoluble, non-toxic
metabolites, when supernatant fractions of liver are added.
The newly derived metabolites are considered to be a complex
of unknown structure. The activity of the supernatants to
promote the secondary reaction varies considerably depending
on the source of the supernatants, and the supernatant from
cockroaches can hardly complete the secondary reaction,
while that from rut liver rapidly finishes the reaction.
The third factor is the effect of the-natural: .
, inhibitor, which exists in insect body' tissues, on the
oxidative . metabolism. The-sUpernatantsof.cockroach fat-body
and middle intestine contain. protein-like natural inhibitor
which depresses the oxidative metaboliem: Ifthe . supernatants
. of the aforedescribed'fat-body or middle intestine are .
'added, the activities of microsomal oxidase systems from.
. rat liver and cockroach fat-body, and the yields of the'
hydroylated Metabolites are considerably lowered. Particularly
the middle intestine supernatant hass quite strong inhibitory
activity. On the other hand, eupernatants from* mammals do
not show this type of activity (Table 3). Even though a lot
-
of work has to be done on the physiological effects of the
natural inhibitor on insect metabolism, it is pr.esently
estimated that the inhibitor is suppressing the detoxication
of rotenone in the bodies of insects by oxidation.
Since the patterns of in vitro enzymatic metabolisms
by rats and cockrOaches resemble very well those of in vivo /398
metabolism observed in orally administered rats or in
cockroaches injected with rotenone, the former in vitro
patterns are interpreted as exact replicas of the metabolism
lof rotenone in each insect or animal. Accordingly, the
selectivity of rotenone has the width of the marginal
selectivities both in the in vivo microsomal, primary
oxidative metabolism and in the portion where the secondary
* reaction participated 10) .
5.2 Selective Toxicity of Parathion-Type Insecticides
Dialkyl phosphate type insecticides have lower
toxicity against mammals when the alkyl group are methyls
than when they are ethyls. However; against insects, both
have the same insecticidal activities with no selectivity.
Plapp and other 133') labeled the methyl ar ethyl phosphate
ester with 32 ' and examined their metabolisms in mammals P
and in insects. They found that, in mammals, the methyl
ester produced non-toxic demethyl compounds as a product
*T.ransl. Note: . ?
-
()stalky/ pkos 'hs..ip cm.c,t,des
pa ratil l 'o 11,
rte. fh o PI
e_. E
of P-O-Methyl splitting, but the ethyl ester did.not yield
deethyl deriVative or, if yielded, only a very little
amount. On the other hand, in insects, dealkylative
metabolism appeared to take place only very difficulty.
4- . Fukami and others13 6) independently fond that there was
an enzyme which demethylated methyl ester insecticides, in
liver supernatant of mammals, using 32 2-markers. This
enzyme acted only at the methyl ester group, and the activity
of that from the mammalian source was high but that of the
insects was quite low. These results agreed well with
Plapp's results described above. Thus the difference in
dealkylations, that is, demethyiation of methyl ester
insecticides to yieid non-toxic deriVative and deethylation
which is difficult to take place, or the difference in the
activities of enzymes that caused the demethylation,
probably the principal cause of the low, toxicity against
mammals and no selectivity among insects.
-
0)P - O -L,t4
OLe me tivy parectkeon
GrS- 1LF CH
vnee I tk
y a g
I Del ra.d. 04.+%lo o fvlefky l tet r a. till' 0 v% 11Ak+txtk t' one s- le-M y I -t- ra.s -t-exc&se_
Aecti-ki N
yaxathor,. ey
-4 Tree. s I o.+ar s Weete * 0 be coYrec.t , e1-te r c4wet&1 or MOV10 yn e rot.ra.-t-h
I rar VI
The demethylation enzyme requites - reduced glutathione
for the reaction. This indicates that the demethylation is
not a simple hydrolysis of the phosphate ester, but a
transfer reaction of the methyl group from the phosphate
ester to glutathione. Experiments using'a 14 0-Methyl marker 157)
proved that.the'transfer was assisted.ty a kind:of
glutathione-transferase. .
-
C}130>
AluFb P-0 NO z
(7. e. )
- Sumithion
Sumithion, - which.i also a methyl phosphate insecticide
with only lightly.different Chemical structure .from that -.
of methylparathion, ha only 1/36 the toxipIty of that of .
methylparathion. 'This selectivity was aIso studied using . .
various markers". .First, it was found that th e degradeion
velocities of-methylparathion and - sumithion bY the afor-.-
described demethylase were nearly identical, and, the possible
eelebtivity owing to this enzyme was de1,1ied136,138)...' Other
possible . Participating enzymes Were sOught after but none
of . the results uld eXplain,the.selectivitY 138) . Next, -
Miyamoto and others 139-14,2 ) administered sumithiOn,'methyl-
parathion and their oxons to Mammalei and examined their .
activations in 'thebodies, their-degradations, degrees of. ,
inhibition of cholinesterase actiVities, and mobilities.in .
the tissues. They found that sumioxOn .penetrated mUch more
slowly into brains than methylparaoxon, and the animals'
brain-nerves were not ttacked seriously, and concluded
that the,difference in the Mobilities into the brain is
the main cause of the selectivities. However, Hollingworth
and others 143) discovered that, when a large dose of
sumithion was given to mice, almost all of the sumithion
Ut
-
-64
degraded in the bodies, and about 80% of the degradation
products was demethyl derivative, and they, therefore,
proposed that the demethylation was the critical factor
in their selectivities, thus casting doubts on Miyamoto
and. others' brain- blodvessel. theory.
The cause of the low toxicity of sumithion is still
a subject of serious debate, and perhaps no one single factor
la the critically important, low toxicity cause, and a
number of factors may be contributing their influences
simultaneously. It might be too optimistic to give any
conclusive explanation of this problem, but the author .
favours the following hypothesis the difference in the
toxicities for animals between sumithion and methylparathion
lies in the difference in the Velocities of the insecticides
in reaching the brains. Owing to the slow mobility of
sumioxon, before the brain nerves are paralyzed, both
sumithion and sumioxon are rapidly detoxicated by the action
ofdemethylase. The low toxicity of sumithion must be a .
summary effect of the two actions.
-
I C.>- '11
Bibliography in jaDanese
33) Fukami, J. and others: Abstracts of Annual Meeting (1968), APplied Zoology and Entomology (Odokon-Koen) (1968) (page missing)
83) Kato, R.: Sites of Action of Drugs (Yakubutsu no Sayoten) (Ed. by Takagi, H.) p. 227, Nankodo
Pub. Co., Tokyo (1968) ' 112) Adachi, M. and others: 15roduction Technology of
Pesticides (Noyakusisangijutsu) 14,19 (1966); 11 (1966).
114) Ishizuka, K. and others: Abstracts of Annual Meeting of Japanese Agricultural Chemical Society p. 249 (Nichinoka Koen Yoshi) (1967).
124) Kuwazuka, S. : Radioisotopes, 16, 37 (1967).
125) Ishida, M.: Abstracts of Japan - U.S.A. Pesticide Seminar (Nichibei Noxaku Seminar Koen Yoshi) 189 (1967)
126) Kakinoki, K. and others: Abstracts of Meeting of Japan Plant Pathology Society (Nippon Shyokubutsu Byori Gakkai Koen Yoshi) 34 (1968).
127) Ishida, M. and others: Abstracts of Annual Meeting of Japanese Agricultural Chemical Society p. 48 (Nichinoka Koen Yoshi) (1969).
128) Nishiki, 111. and others: Abstracts of Meeting of Japan Plant Pathology Society (Nippon Shyokubutsu Byori Gakkailoen Yoshi) 189 (1968); Abstracts of Annual Meeting of Japanese Agricultural Chemical Society, p. 250 (Nichinoka Koen Yoshi) (1968). .
129) Uesugi, Y. and others: Abstracts of Meeting of Japan Plant Pathology Society (Nippon Shyokubutsu Byori Gakkai Koen Yoshi) 372 (1968).
130) Tanken, S. (or Tan, K.) and others: Abstracts of Annual Meeting of Japanese Agricultural Chemical Society, p. 149 (Nichinoka Koen Yoshi) (19 69).
131) Fukami, J.: Abstracts of Annual Meeting of Japanese Agricultural Chemical Society, p. 149 (Nichinoka Koen Yoshi) (1969).
132) Tomisawa, O. and others: Abstracts of Mee