water content of ground squirrel and laboratory rat tissues

7/29/2019 WATER CONTENT OF GROUND SQUIRREL AND LABORATORY RAT TISSUES

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comp. Biochem. Physiol.,7967, vol.22, pp.75 to 80. pergamon press. printed in Great Britain

WATER CONTENT OF GROUND SQUIRREL ANDLABORATORY RAT TISSUES*c. L. BINTZ and M. L. RIEDESEL .Department of Biology, University of New Mexico,Albuquerque, New Mexico 87106, U.S.A.

(Receited 20 Decunber 7966)Abstract-l . Water contents of several tissues from control and water-deprivedlaboratory rats (nonhibernator), Citellus tridecemlineatrzs and C. lateralis(hibernators) were analyzed.2. In water-deprived laboratory rats all tissues analyzed were dehydrated.Dehydration was consistent among tissues.3. In water-deprived c. tridecemlineatus znd c. lateralis only blood wasconsistently dehydrated, liver had an increased water content, and all othertissues analyzed did not vary from respective tissues of control animals,4' In ground squirrels the decrease in water content of blood appears to bea water-conserving mechanism, The increase in water content of the liver maybe unique to mammalian hibernators,

INTRODUCTIONTornneNcn of mammalian hibernators to deprivation of drinking water (negativewater balance) is a function of many factors, aligned into two categories:'exiernaland internal (Bintz, 1965). External factors include physical variables of theenvironment such as temperature and vapor pressure. Internal factors includeresponses of physiological systems 'vvhich reduce water loss such as inactivity,lowered body temperature, concentration of urine and production of dry feces.A physiological response which may be of importance in increasing toleranceto negative water balance is shifts of water among tissues. It is probable thatcertain tissues are more tolerant to changes in water content than others. Watercontents of skin and skeletal muscle have been reported to vary when the animalis under little stress (Lepkovsky et al., 1957). Skin and skeletal muscle represenrconsiderable mass and during negative water balance may serve as souices ofwater for tissues whose water contents are more critical (e.g. heart, nervous system).Mammalian hibernation involves extended periods of inactivity resulting inlimited or no consumption of food or water. Negatil,e water balance and tiJsuedehydration have been described during hibernation of Cttellus lateralis and.C. spilosoma (Riedesel et a1.,1.964).This study was initiated to test the extent to r,vhich water metabolism of hiber-nators may be unique and advantageous during periods of negative water balance* Supported by the National Science Foundation grant, GB216.

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76 G. L. BrNrz eNt M. L. RrroBsBrother than hibernation. Two hibernating species, C. lateralzs (golden-mantledground squirrel) and C. tridecemlinealzs (thirteen-lined ground squirrel), and anonhibernator, the laboratory rat (Cheek-Jones strain), were studied. Twelvelaboratory rats were studied; six of them served as control animals. Five controland five experimental animals of each species of ground squirrel were studied.Water content of various tissues in animals having had water ad lib. and in water-deprived animals was measured.

MATERIALS AND METHODSThe 30 per cent weight loss was selected because this weight loss representedconsiderable strain, was tolerated by all animals and gave reproducible changesin water content of tissues.Control animals were sacrificed while on water ad lib. Experimentalanimals were deprived of drinking water and sacrificed after losing 30 per cent oftheir original body u'eight. Control and experimental animals had laboratory chow(Wayne Blox Lab Chow, 7-8 per cent water content) available at all times. Animalswere sacrificed by decapitation to facilitate obtaining blood samples and drainingblood from tissues. Duplicate tissue samples of 0'1-1'5 g were removed from each

animal for analysis. Tissues were weighed and dried in preweighed aluminumtares. With the aid of an assistant wet tissue weights were measured within 2 minafter dissection to reduce errors from evaporation following dissection. Weighingswere made on a type LCB analytical balance (Denver Fire Clay Co.). Tissues weredried for 14-18 days to a constant weight ( t 0'003 g) in an electric oven at 60 + 1'C.Drying at this temperature minimized loss of volatile material.Statistical analyses were made in accordance with methods discussed bySchueier (1953). Differences at the 95 per cent confidence level were consideredsignificant.

RESULTSMean time required for 30 per cent weight loss was 6 days for six laboratory

rats and 16 days for ten ground squirrels. All rats lost 30 per cent of original bodyweight in 5-6 days whereas the time required for 30 per cent weight loss by groundsquirrels ranged from 10 to 24 days. When deprived of water, the rate of weightloss by laboratory rats was consistent from animal to animal whereas rate of w-eightloss was variable among ground squirrels. Few of the animals ate after the first24 hr without drinking water.Laboratory rats. All tissues of water-deprived laboratory rats were dehydratedcompared to respective tissues of control rats (P


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WATER CONTENT OF GROUND SQUIRREL AND LABORATORY RAT TTSSUES 77control tissues (P


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78 G. L. BrNrz aNo M. L. RrsossrlCitellus lateralis. Skeletal muscle, kidney and heart from water-deprived andcontrol animals had respectively similar water contents (P: 0.05-0.8) (Table 3).Blood and lungs of experimental animals were dehydrated (P


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WATER CONTENT OF GROUND SQUIRREL AND LABORATORY RAT TISSUES 79presented in this study give additional support to the hypothesis that mammalianhibernators have unique water metabolism. Water and solids were lost at similarrates by water-deprived ground squirrels. At the same time blood was dehydrated,most tissues remained hydrated and liver became over-hydrated. TLe Lverappears to hold a key position regarding water metabolism. perhaps the liverremoves water from the blood and thereby keeps kidney excretion of solids andwater near normal. On the other hand, water metabolism in all other tissues isalso_s_omewhat unique since all tissues remain hydrated when blood is dehydrated.Movement of water from blood to liver has been described by other investigatorsto occur in several species. In rabbits Marshall et at. (1931) induced fevei withcocaine and demonstrated a significant increase in water content of the liver and adecrease in blood water content within 30 min after injection. Barbour & Tolstoi(1923) observed decreased water content of the blood of dogs following a periodin a cold water bath. DeBoer (1945) noted a decrease in blood water content indogs following 10 days of water deprivation.Decreased water content of blood may be a general response to stresses suchas cold' negative water balance and others. Decreased water content of bloodresults in decreased water content of peripheral tissues, which may result in(1) decreased heat loss and subsequent decreased metabolic expenditure, and (2)decreased vapor pressure of the skin and subsequent decreased evaporative r,vaieiloss (although evaporation may be insignificant (Fisher & Manery, i967).The increase in water content of the liver in water deprived ground squirrelsmay impiy (1) water storage in the liver and/or (2) reduced metabolic activity ofthe liver. In z;itro studies demonstrate that water content of several tissues inhomeotherms increases as the tissues are cooled (Fisher & Manery, 1967). Coldreduces activity of ion diffusion and active transport systems, intra- anj extra-cellular compartments become isotonic, and water diffuses into cells in response tothe internal colloidal osmotic pressure. However, this response to cold appearsnot to be crperable in hibernators, including ground squirrels (Fisher & M anery ,-l-967).It seems probable then that increased water content of the liver is due towater storage. Marshall et al. (1931) concluded the extra water in the liver of thehyperthermic rabbits may have been shunted from blood for storage purposes.It rn'ould be interesting to determine how' long (in terms of negative watei baiance;ground squirrels can maintain an increased water content in the liver. After a.30 per_ cent body weight loss the muscle mass of water-deprived ground squirrelsis markedly reduced although considerable fat still remains.

REFERENCESAoorpn E. F. (1947) Ijrges to eat and drinkin rats. Arn.J. physiol. lst,r10-12s.Bansoun H. G. & Tor-sror E. (1923) Heat regulation and water exchange-Il. The role ofthe water content of the blood, and its control by the nervous system. A*. j.physiol.67,378,387.BrNrz G. L. (1965) Seasonal tolerance of Citellus tridecemlineatus, Citellus lateralis, and thelaboratory rat to deprivation of drinking water. M.S, thesis, University of New Mexico.


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80 G. L. BtNtz eNo M. L. Rrnosspl-Cook S. F., Cnarmn C. & KrNyoN K. (1952) A rapid titrimetric method for determining thewater content of animal tissues. Science, N. y. 115, 353-354,DnBonn B. (1945) Changes in the blood during chronic and acute dehydration. A*.J.Physiol. 145, 754-757.Frsnsn K. C. & MaNBnv J. F. (1967) Water and electrolyte metabolism in heterotherms. InThird Int. Symp. Natwal Mammal..I{zb. University of Toronto, T3-76 September 1965.Oliver & Boyd, Edinburgh.LBprovsrv S,, LvrrnN R., Fr-nmrNc D., Nacuvro M. & DIrrrc M. (1957) Gastrointestinalregulation of water and its effect on food intake and rate of digestion. Am.J. Physiol.l88,327-337.Mensner,r- H., Avonr-orre B. & Baneoun H. (1931) Heat regulation and water exchange.A*. J. Physiol.98, 615-624.Rrronsnr- M. L., Kr,rrvpsul'nn L. R. & BnNar-r,v N. R. (1964) Tolerance of. Citellus lateralisand C. spilosoma fot water deprivation. Ann. Acad. Sci. Fenn. A, IY,7U27,377-388.Scnunr-un F. W. (1953) A guide to statistics. J. A*. Dietetic Ass.29,861-1123.

water content of ground squirrel and laboratory rat tissues

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