JACC Vol. 9. No.6June 1987:1235-42

Relation Between Coronary Artery Stenosis and Myocardial PurineMetabolism, Histology and Regional Function in Humans

WILLEM FLAMENG, MD,* JOHAN VANHAECKE, MD,! HERMAN VAN BELLE,:j:MARCEL BORGERS, DRSC,:j: LUC DE BEER, DRSC,* JAAK MINTEN, DRSet

Leuven and Beerse, Belgium

1235

In 54 patients undergoing elective or emergency aorto­coronary bypass grafting, angiographic and electrocar­diographic changes were studied. Five patients with un­stable angina and fivepatients with evolvingmyocardialinfarction were included. .High energy phosphate me­tabolism and the histologic appearance of the myocar­dium were analyzed in transmural biopsy specimens ac­quired at the time of surgery.

In patients without anterior infarction on the elec­trocardiogram, severe stenosis of the left anterior de­scending coronary artery resulted in a reduction of an­terior wall motion that was associated with a partialdepletion of the adenylate pool. Mitochondrial function,however, remained intact: the adenosine diphos­phate/adenosine triphosphate ratio, the energy chargeand the creatine phosphate/adenosine triphosphate ratiowere in the normal range . Histologic assessment dem­onstrated viable myocardium with a high incidence ofatrophic cells.

In evolving myocardial infarction, 170minutesof acute

The effect of acute coronary artery occlusion on high energyphosphate metabolism has been exten sively studied in ex­perimental animals (1-5). Under these conditions a rapiddegradation of adenine nucleotides has been demonstratedand a critical level of adenosine triphosphate (ATP) wasproposed as the triggering mechan ism for irreversible myo­cardial cell damage (I). Acute coronary artery obstructionin humans, however , is usually preceded by a significantdegree of coronary artery stenosis and the influence of sucha chronic , progressive stenosis on purine metabolism, myo-

From the *Department of Cardiovascular Surgery and the t De­partment of Cardiology, University Clinic Gasthuisberg, Leuven and thet Department of Cell Biology, Janssen Pharinaceutica Research Labora­tories, Beerse, Belgium. This study was supported by a grant from theNationaal Fonds voor Wetenschappelijk Onderzoek, Brussels. Belgium.

Manuscript received March 31, 1986; revised manuscript received No­vember 19, 1986, accepted December 12, 1986.

Address for reprints: Willem Flameng , MD. Department of Cardio­vascular Surgery. U.Z. Gasthuisberg . Herestraat 49, B-3000 Leuven, Bel­gium.

©1987 by the American College of Cardiology

coronary artery obstruction resulted in anterior wallakinesia associated with a decrease of the sum of theadenylates to 52% and of creatine phosphate to 16% oftheir normal value (p < 0.05). The nucleosides accu­mulated; their major fraction (91%) was inosine. Theadenosine diphosphate/adenosine triphosphate ratio in­creased from 0.14 ± 0.04 to 0.49 ± 0.20 (p < 0.01) andthe energy charge decreased from 0.924 ± 0.021 to 0.660± 0.169 (p < 0.01). Ultrastructure examination revealedirreversible cell damage in at least the subendocardiallayer.

These results suggest that the energetic base of re­duced contractility due to severe coronary artery stenosisis different from that in acute coronary obstruction: thedecrease in contractile function cannot be explained bya reduced oxidative phosphorylation but may be relatedto an impaired energy utilizationat the myofibrillarlevel,in analogy with the postischemic reperfused stunnedmyocardium.

(J Am CoilCardiol1987;9:123S-42)

cardial function and cell viability has not been established.Recurrent episodes of regional ischemia associated with asevere degree of coronary stenosis may finally influencethese variables. Indeed. recent experimental evidence sug­gests that intermittent myocardial ischemia induces persist­ent contractile dysfunction (6) , changes in cell volume reg­ulation (5) and depre ssion of the adenine nucleotide pool(4,5) despite the prevention of cell death by adequate reflow .

We studied high energy phosph ate metabolism and his­tology in the myocardium of patient s with coronary arterydisease at the time of surgery and related these findings tothe degree of coronary stenosis and to regional wall motionas measured on the preoperative angiogram. Because thestudy group included patients with stable angina pectoris,unstable angina pectori s and evolving or healed myocardialinfarction; a wide range of coronary stenosis progressing tocomplete occlusion was examined .

Of special interest are the observations on the rate ofadenine nucleotide degradation in patients with evolving

0735-1097/87 /$3 .50

1236 FLAMENG ET AL.MYOCARDIAL PURINE CATABOLISM IN CORONARY ARTERY DISEASE

JACC Vol. 9, No.6June 1987:1235-42

myocardial infarction because of possible discrepancies be­tween experimental animals and human patients in terms ofischemia tolerance of the myocardium and time constraintsfor effective treatment after the onset of acute coronaryartery obstruction.

MethodsStudy patients. Fifty-four surgical patients with obstruc­

tive coronary artery disease were included in the study. Thepatients (6 women and 48 men) were 47 to 68 years oldand all underwent aortocoronary bypass grafting. All pa­tients had ventriculographic and coronary arteriographic ex­aminations within 8 weeks before surgery. Five patients hadunstable angina pectoris. Another five had coronary bypasssurgery performed as an emergency procedure because ofevolving myocardial infarction; four of these patients de­veloped their acute infarction during cardiac catheterizationor coronary angioplasty. The duration of occlusion of theleft anterior descending coronary artery before revascular­ization was 170 ± 25 minutes.

Catheterization and angiography. In each patient an­giograms of the left ventricle were obtained in the 30° rightanterior oblique and the 45° left anterior oblique projection.Coronary angiograms were performed using the Sones tech­nique. Ejection fraction was calculated and wall motion wasmeasured from the frontal end-diastolic and end-systolicoutlines of the left ventricle as described previously (7).The degree of stenosis in the left anterior descending coro­nary artery was determined by measuring the prestenotic,poststenotic and intrastenotic vessel diameter in both pro­jections. The mean intraluminal pre- and poststenotic area(rnm') was calculated using the catheter diameter for cali­bration. The percent stenosis was calculated by expressingthe intraluminal area at the narrowest site of the stenosis asa percent of the mean pre- and poststenotic area.

Patient groups. The patients were classified into groupsaccording to the degree of stenosis of the left anterior de­scending coronary artery and electrocardiographic (ECG)signs of anterior infarction. Group I comprised 16 patientswith 70 to 89% stenosis. Group II comprised 27 patientswith 90 to 100% stenosis; of whom 5 had unstable angina.Only patients without electrocardiographic signs of previousanterior infarction were selected for groups I and II. GroupIII comprised five patients with evolving anterior infarction;acute occlusion of the left anterior descending coronaryartery was confirmed during surgery in all five. Group IVcomprised six patients with electrocardiographic signs ofprevious anterior infarction (healed infarction).

Myocardial biopsy. Two transmural needle biopsyspecimens measuring 1.5 mm in diameter (Tru-cut biopsyneedle, Travenol Laboratories) were obtained from the cen­ter of the area perfused by the left anterior descending coro­nary artery. These specimens were obtained when the pa­tients were on cardiopulmonary bypass but before any of

the distal or proximal coronary anastomoses were per­formed. Each specimen used for microscopic studies wasdivided into a subepicardial and subendocardial sample.

Biochemicalanalysis. The transmural biopsy specimenswere immediately (within 3 seconds) cooled in liquid ni­trogen and stored at - 80°C. Adenosine triphosphate andcreatine phosphate were determined by luminometry (LKB1250; ATP luminescence kit, CLS-Boehringer). Nucleo­tides, nucleosides and the purine bases were separated usinghigh pressure liquid chromatography in one single run (gra­dient on reversed phase Cl8 column) (8). Inorganic phos­phate was measured using an automated malachite greenmethod. Tissue contents are calculated as micromoles pergram dry weight.

Myocardial histology. The biopsy specimens were im­mersed in fixative containing 3% glutaraldehyde and 90rnmol/liter oxalate adjusted to pH 7.4 with normal potassiumhydroxide. Further processing for light and electron mi­croscopy was done as described previously (9).

In an attempt to quantify the degree of cell degenerationin the different layers of the myocardium, 100 myocardialcells that were sectioned through the nucleus were exam­ined. This was done on semithick toluidine blue-stainedsections of the subepicardial and subendocardial parts of thebiopsy samples. The percent of normal cells was calculated(9).

Ultrastructural changes in the myocytes were analyzedin several electron micrographs that were taken at randomfor both areas (subepi- and subendocardial), No attempt wasmade to quantify the degree of subcellular myocardial dam­age.

Statistical methods. Biochemical, functional andhistologic data are expressed as mean values ± standarddeviation. For statistical analysis one way analysis of var­iance was performed between groups. Unpaired t test versusgroup I was performed when the F value was significant atthe 0.05 level.

ResultsCoronary artery stenosis and high energy phosphate

metabolism (Table 1). Data on myocardial creatine phos­phate, inorganic phosphate, nucleotides, nucleosides andthe purine bases in the different groups are listed in Table1. As coronary artery stenosis progressed, a loss of highenergy phosphates was observed. With severe stenosis (groupII), the sum of adenylates decreased to 73% of the valuemeasured in patients with mild stenosis (group 1). Adenosinetriphosphate (ATP) content dropped to 74%. As long as thecoronary artery was not acutely obstructed, purine catabo­lism was not associated with increased tissue content ofnucleosides and purine bases (Fig. 1). However, when acuteocclusion of the coronary artery developed (group III), thesum of adenylates dropped to 54% of the value found withmild stenosis. Then adeny1ate catabolism was reflected by

JACC Vo!. 9, No.6June 1987:1235- 42

FLAMENG ET ALMYOCARDIAL PURINECATAROLISM IN CORONARY ARTERY DISEASE

1237

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30

Figure 2. Myocardial tissue content of adenine nucleotides, nu­c1eosides and purine bases in group [ patients with 90 to 100%stenosis without infarction (open bars ) and in group III patientswith evolving infarction (hatched bars ). Values are means ±SEM. **p < 0.01 versus 90 to 100% stenosis; ***p < 0.001.A + I = adenosine + inosine; ADP = adenosine diphosphate;AMP = adenosine monophosphate; ATP = adenosine triphos­phate; DW = dry weight; H + X = hypoxanthine + xanthine;NrNsB = sum of nucleotides, nucleosides and bases.

high tissue levels of nucleosides and purine bases (Fig. I[lower panel] and 2). Obviously these catabolites were notwashed out from the ischemic tissue: compared with severestenosis the sum of nucleotides, nucleosides and purine basesremained constant (Fig. 2). Nucleosides, which represented

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1238 FLAMENG ET AL.MYOCARDIAL PURINE CATABOLISM IN CORONARY ARTERY DISEASE

JACe Vol. 9, No.6June 1987:1235-42

Figure 3. Relation between the degree of coronary stenosis andmyocardial mitochondrial function as assessed by the ADP/ATPratio (0) and theenergy charge (e). Values are means ± SEM.*** P < 0.001 versus group I. Abbreviations as in Figure 2.

only 0.1 % of the sum of nucleotides, nucleosides and basesin mild stenosis, increased during acute coronary arteryocclusion to 19%. The major fraction of the accumulatednucleosides was inosine: 2.65 ± 1.34 J.Lmollg or 91% ofthe nucleosides. The adenosine diphosphate (ADP)/ATP ra­tio, which increased slightly from 0.14 to 0.17 when thedegree of stenosisprogressedfrom mild to severe, increasedfurther to 0.49 in acute coronary occlusion (Fig. 3). Theenergy charge (ATP + 1/2 ADP)/(ATP + ADP + aden­osine monophosphate [AMP]) (10) decreased slightly from0.921 to 0.904 whencoronarystenosisprogressed frommildto severe. After acute coronary occlusion the energy chargefell abruptly to 0.660 (Table 1 and Fig. 3).

Creatine phosphate decreased during acute occlusion tovery low levels: myocardial tissue contents decreased to17% of the value measured in mild stenosis (Fig. 1). Afterchronic infarction (group IV), purine content recovered tolevels comparable with those in severe stenosis without in­farction as did creatine phosphate, ADP/ATP ratio and en­ergy charge (Table 1).

Histologic findings related to coronary artery stenosis(Table 2). At the light microscopic level, myocardial cellchangeswere quantifiedin subepicardial and subendocardial

biopsy samples as described previously (9) and the percentof completely normal myocytes per sample was calculated.Myocardial cell abnormalities were characterizedmainly bya reduction of the volume fraction of the myofibrils, es­pecially in the perinuclearzones, and by nuclear tortuosity.The frequency of altered cells was significantly increasedin patientsof group II (90 to 100%stenosiswithoutpreviousinfarction). However, interpatient variation is very high inthis group, whichcomprisespatientswithalmostcompletelynormal histologic findings as well as those with a highdegree of myocardial cell abnormalities. Tissue samplesfrom patients having ECG signs of previous anterior in­farction (group IV) uniformly showed a low incidence ofnormal myocytes in the subepicardium and in the suben­docardium: 32 and 17%, respectively.

Myocardial fibrosis wasobservedin only 11 % of samplesin group II. In group IV it was uniformly found in samplesfrom patients with ECG signs of previous infarction.

At the ultrastructural level, the myocardium in samplesfrom group I revealed a normal subcellular structure. Ingroup II, ultrastructural changes consisted of myofibrillaratrophy, presence of many small mitochondria, glycogenaccumulation and polymorphism of the nucleus (9, II) (Fig.4). In some cases ultrastructure was completely normal. Anormal subcellular structure was often associated with ahistory of unstable angina related to this area (Fig. 5).

Ultrastructural changes related to acute myocardial is­chemia (1,12) were rare in all groups except group III(evolving myocardial infarction). In groups I, II and IV,only the lack of intramatricial granules in the mitochondriaand someswellingof the mitochondrial matrixwerenoticed.

In the group with evolving myocardial infarction (groupIll), ultrastructural degenerative changes were dramatic, inall subendocardial samplesirreversible myocardialcell dam­age was found: rupture of the sarcolemma, mitochondriacontaining flocculent densities, intracellularedema and nu­clear chromatin clumping (Fig. 6). In contrast, subcellularinjury to the subepicardial cells was reversible: only mildto severe mitochondrial swelling without sarcolemmal andnuclear changes was observed (Fig. 6).

Regional left ventricular wall motion (Table 2). Whencoronarystenosisprogressedto 90%, segmentalwallmotionremained in the normal range. With stenosisof 90 to 100%,

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Table 2. Myocardial Regional Wall Motion and Histology in 49 Patients

%Normal Myocytes*

AWM* (%) Epi Endo Total Fibrosis

Group I (n = (6) 48.9 ± 8.9 83 ± 14 79 ± 18 82 ± 14 o of 16 (0%)Group II (n = 27) 34.9 ± 9.9* 59 ± 33:1: 51 ± 30:1: 55 ± 30:1: 3 of27 (11%)Group IV (n = 6) 24.8 ± 10.9* 32 ± 28* 17 ± 9* 24 ± 18* 6 of6 (100%)F value 5.5411 6.61 11 12.511 10.711

Statistics as in Table I. *Values are means ± SD. AWM = anterior wall motion; Epi = subepicardiallayer; Endo = subendocardial layer.

JACC Vol. 9, No.6June 1987: 1235-42

FLAMENG ET AI..MYOCARDIAL PURINE CATABOLISM IN CORONARY ARTERY DISEASE

1239

Figure 4. Electron micrograph from a subendocardial biopsy sam­ple of a hypokinetic anterior wall in a patient from group II. Thissection shows a severely altered myocyte. There is considerablereduction of the myofibrillar volume fraction in the center of themyocardial cell. The sarcolemma appears intact whereas the nu­cleus (n) is tortuous; most mitochondria are small in size and largeareas of glycogen (gl) fill up the cytosol (original magnificationx 2,250, reduced by 25%).

Figure S. Electron micrograph from a subendocardial sample ofthe anterior wall in a patient from group II with unstable angina.In this sample, myocardial structure is normal except for someclearing of the mitochondrial matrix (arrows) (original magnifi­cation x 13,200, reduced by 25%).

however, wall motion declined to 72% of its initial value.With complete acute coronary artery occlusion, paradoxicalmovement of the segment occurred. This paradoxical move­ment was noted on the preoperative left ventriculogram inone case and was observed during surgery in the other four

Figure 6, a, Electron micrograph of a subendocardial sample ofthe anterior wall in a patient with an evolving infarction due toocclusion of the left anterior descending coronary artery. The myo­cardial cell is irreversibly damaged: the sarcolemma is disrupted(arrows) and the mitochondria show the typical flocculent densities(arrowheads) that are hallmarks of irreversibility. The nucleus(0) shows clumping and margination of chromatin. b, Electronmicrograph of a subepicardial sample of the anterior wall in thesame patient. The sample was taken 160 minutes after the onsetof coronary occlusion. Note that the ultrastructure of the myocyteis normal except for a very slight clearing of the mitochondrialmatrix. (Original magnification in a and b x 13,200, reduced by25%.)

cases. In these four cases a left ventriculogram was notperformed in the acute stage of evolving infarction. In groupIV (patients with ECG evidence of previous infarction),segmental wall shortening attained only 50% of normal val­ues.

1240 FLAMENG ET AL.MYOCARDIAL PURINE CATABOLISM IN CORONARY ARTERY DISEASE

JACC Vol. 9. No.6June 1987:1235-42

DiscussionMyocardial purine metabolism in man. This study

deals with the relation between coronary artery stenosis andmyocardial purine metabolism , histology and regional func­tion. In humans, this relation has not been previously es­tablished . Data on human myocardial tissue contents ofnucleotides are scarce, and usually restricted to the mea­surement of adenosine triphosphate (ATP) (13). In exper­imental animals, on the other hand, purine metabolism andits catabolism during ischemia are relatively well known(1-5). Our clinical results show that high energy phosphatemetabolism in humans is comparable with that found inexperimental animals. Under normoxic conditions, the com­position of the adenine nucleotide pool is similar in thehuman and the canine heart. We found that the adenosinediphosphate (ADP) and monophosphate (AMP) content inthe human myocardium, expressed as a percent of the totaladenylate pool, is 12 and 2%, respectively, when coronaryartery stenosis does not exceed 90%. Comparable valuesare reported in experimental animals with normal coronaryvessels (3- 5, 14-17). The adenylate charge (10) in thehuman heart as reported in our study (0 .921 ± 0.028, mean± SD) is clearly in the same range as the values found inanimal hearts (0.919 to 0.928) (3,4,14-16). Also the ratiobetween creatine phosphate and ATP (1.50 in this report)is comparable with values reported in animal studies (1.29to 1.71) (3,4,14-16). Only values obtained with nuclearmagnetic resonance techniques seem to produce a slightlyhigher creatine phosphate/ATP ratio (18).

Relation between coronary stenosis, purine metabo­lism, histology and regional function. Our results indicatethat severe coronary stenosis is associated with a 20 to 30%reduction in myocardial nucleotide content. It may be as­sumed that in the presence of such severe stenosis, inter­mittent periods of myocardial ischemia lead to purine break­down (15,17). Purine catabolism induces an accumulationof nucleosides and bases in the myocardium, but these sub­stances are readily washed out as long as there is no completeocclusion of the vessel. Next , further catabolism to hypo­xanthine represents an almost irreversible loss of the "back­bones" ofthe adenylate pool. Such a washout of nucleosidesand purine bases was shown previously by de long andGoldstein (19) and Kugler (20) when they obtained highlevels of inosine and hypoxanthine in the coronary sinusblood during pacing and exercise-induced ischemic epi­sodes . De novo synthesis of adenylates is an extremely slowprocess (4), and it is probably not optimal in the presenceof a severe coronary stenosis .

Severe left anterior descending artery stenosis was alsoassociated with a 30% reduction in regional wall motion .This confirms the results of a previous study (7). Our ob­servation that the reduction in the adenylate pool parallelsthe reduction in local contractility does not necessarily imply

that the depression of local function is caused by this re­duction in the adenylate pool. Indeed, the ADPIATP ratio,the energy charge and the creatine phosphate levels are inthe normal range and this is very suggestive for an intactmitochondrial function, that is, a normal energy production.We realize however that the ADP/ATP ratio, obtained byour methodology, is not an optimal estimate of mitochon­drial function . The problem is that "cytosolic" ADP con­centrations cannot be measured with any existing technol­ogy. Even with nuclear magnetic resonance techniques theADP concentration can only be estimated by subtracting theATP beta-phosphate peak from that of the gamma-phosphatepeak and the error associated with this measurement is rel­atively high (21). Nevertheless, our values for creatine phos­phate and energy charge are accurate and they are acceptableindexes of mitochondrial function .

A near normal energy production may well be associatedwith postischemic myocardial dysfunction, reduced aden­ylate pools and normal or elevated creatine phosphate levels(21,22). Experimental evidence exists that this entity, calledmyocardial stunning, is due to a deficiency of the creatinephosphate shuttle , at the level of the myofibrillar isoenzymeof creatine kinase (23). The same phenomena, reduced wallmotion, reduced adenylate pool, normal mitochondrial func­tion and normal creatine phosphate levels, were found inour group II patients; therefore , myocardial dysfunction mayrepresent a " stunned myocardium " induced by chronic in­termittent ischemia (6). However , recurrent episodes ofischemia not only may induce stunning and purine loss butalso may activate proteolytic systems responsible for my­ofibrillar lysis. A certain degree of myofibrillar lysis wasfound in at least 50% of the myocytes in this subset ofpatients. We reported in previous studies (7,9,11) that thistype of cell degeneration correlates best with reduction inleft ventricular function. It was shown using immunohis­tochemical techniques (24) that fibers with myocytolysis areviable because they retain enzymes and other proteins (cre­atine kinase MB fraction, myoglobin, lactic dehydrogenase[LDH]-l , aspartate aminotransferase [AST]. Also using im­munofluorescence staining Hayakawa et al. (25) demon­strated a similar labeling intensity for Ca2 + and Mg2 + aden­osine triphosphatase and tropomyosin in myocytolytic cellsas in normal muscle cells. Thus, myocytolysis may be areversible form of myocardial alteration that , although itdoes not necessarily lead to cell death and eventual myo­cardial fibrosis (24), may well induce myocardial dysfunc­tion.

Factors producing variations of findings in severe ste­nosis group. In the severe stenosis group there was a widescatter in the biochemical, histologic and functional data .Many factors may contribute to this variation : 1) A smallbiopsy specimen is assumed to be representative of a rel­atively large area. Hearse et al. (3) showed that there isalready a large variation in biochemical values when a large

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FLAMENG ET AL.MYOCARDIAL PURINE CATABOLISM IN CORONARY ARTERY DISEASE

1241

number of simultaneously obtained samples are removedfrom a homogeneously perfused subepicardial zone duringthe same cardiac cycle. 2) Analytic errors may be relatedto the small size of the biopsy specimens. 3) Assessmentof the degree of stenosis is not completely accurate becausethe length of the stenotic segment is not taken into account.4) The determination of regional wall motion as an indexof regional contraction may be inaccurate. Axis shorteningas such may not completely reflect segment movement, andprevious medication (beta-adrenergic blocking agents) mayinfluence contraction. There is also a time interval betweenangiography and surgery so that correct extrapolation of wallmotion data to the moment of tissue sampling remains ques­tionable. 5) The absence of electrocardiographic evidenceof anterior infarction does not exclude the presence of an­terior wall infarction, a factor that may account for someof the differences between the group with the highest gradestenosis and those with lesser degrees of stenosis. On theother hand, some of the variation may be real because coro­nary stenosis is a dynamic process: progression of the dis­ease may be fast or slow, coronary spasm may influencethe degree of stenosis from one minute to another and theoxygen supply and demand balance of the heart is not stable.This group still comprises some patients with normal purinelevels, normal histologic features and normal wall motion.Therefore, actual biochemical and functional measurementsmay represent no more than a "snap shot" of an evolu­tionary process.

Myocardial purine catabolism during evolving in­farction. Purine catabolism during evolving myocardial in­farction in humans has not been described before. Our re­sults indicate that, in patients with a history of coronaryartery disease, the rate of purine catabolism during morethan 2 hours of acute coronary occlusion is not the same asthat found experimentally in the dog heart. In patients, aden­osine triphosphate decreased to 43% of its initial value (thatis, 95% stenosis). In contrast, in dogs, adenosine triphos­phate dropped to 6% of its normal value after only 40 min­utes of acute coronary artery occlusion (1). This differencein tolerance to ischemia is most probably due to the presenceof a better developed collateral circulation in patients withcoronary artery disease as compared with healthy experi­mental animals. However, the pattern of purine catabolismin patients with acute coronary obstruction is similar to thatin dogs with acute coronary occlusion. Adenosine mono­phosphate increases and the nucleosides and bases accu­mulate extensively (Fig. 2). The main component of thenucleosides during occlusion is inosine: this component rep­resents 90% of the nucleoside pool, the remaining 10%being adenosine. The histologic findings in acute infarctionin humans are also comparable with those in dogs (1). Mainly,the subendocardial part of the myocardium is irreversiblydamaged. This implies that the reduction of ATP in theviable portion of the myocardium at risk will be less than

the evaluation of a transmural and partly necrotic samplemay suggest.

In the subclass of patients with healed anterior infarc­tion, the same level of nucleotides was found as in patientswith severe stenosis. However, the incidence of cell de­generation was higher and myocardial fibrosis was uni­formly observed. This fibrous replacement of myocytes mayexplain the extremely low values of regional contractilefunction in this subclass despite relatively high levels ofhigh energy phosphates.

Conclusions. Progressive coronary artery stenosis ap­pears to result in a partial destruction of the adenylate pool,probably as a result of recurrent short periods of purinecatabolism. Mitochondrial function, as estimated by theADP/ATPratio, energy charge and creatine phosphate/ATPratio is not impaired so that the associated reduction inregional contractile function cannot be explained by a de­creased production of high energy phosphates. The energeticbase of this type of hypokinesia is probably an impairedenergy utilization with reduced ATP splitting at the myofi­brillar level as in the postischemic reperfused "stunned"myocardium (22,23). A reduced volume fraction of myo­fibrils, however, can be demonstrated histologically andmay be the basis for this partial loss of function. Suddencomplete obstruction of a coronary vessel, however, resultsin a massive degradation of high energy phosphates and anaccumulation of mainly inosine in the ischemic myocar­dium. Mitochondrial function is severely impaired, as re­flected by a sudden complete loss of contractile function.The rate of adenine nucleotide degradation is much slowerthan would be expected from animal studies. After 170minutes of occlusion, ultrastructural evidence of cell ne­crosis occurs in at least the subendocardiai part of the myo­cardium at risk.

We express our gratitude to Agnes Goethuys for preparing the manuscript.

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