Myocardial Purine Research Articles

Hot shot induction and reperfusion with a specific blocker of the es-ENT1 nucleoside transporter before and after hypothermic cardioplegia abolishes myocardial stunning in acutely ischemic hearts despite metabolic derangement: Hot shot drug delivery before hypothermic cardioplegia

Simultaneous inhibition of the cardiac equilibrative-p-nitrobenzylthioinosine (NBMPR)-sensitive (es) type of the equilibrative nucleoside transport 1 (ENT1) nucleoside transporter, with NBMPR, and adenosine deaminase, with erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA), prevents release of myocardial purines and attenuates myocardial stunning and fibrillation in canine models of warm ischemia and reperfusion. It is not known whether prolonged administration of hypothermic cardioplegia influences purine release and EHNA/NBMPR-mediated cardioprotection in acutely ischemic hearts. Anesthetized dogs (n=46), which underwent normothermic aortic crossclamping for 20 minutes on-pump, were divided to determine (1) purine release with induction of intermittent antegrade or continuous retrograde hypothermic cardioplegia and reperfusion, (2) the effects of postischemic treatment with 100 μM EHNA and 25 μM NBMPR on purine release and global functional recovery, and (3) whether a hot shot and reperfusion with EHNA/NBMPR inhibits purine release and attenuates ventricular dysfunction of ischemic hearts. Myocardial biopsies and coronary sinus effluents were obtained and analyzed using high-performance liquid chromatography. Warm ischemia depleted myocardial adenosine triphosphate and elevated purines (ie, inosine>adenosine) as markers of ischemia. Induction of intermittent antegrade or continuous retrograde hypothermic (4°C) cardioplegia releases purines until the heart becomes cold (<20°C). During reperfusion, the levels of hypoxanthine and xanthine (free radical substrates) were >90% of purines in coronary sinus effluent. Reperfusion with EHNA/NBMPR abolished ventricular dysfunction in acutely ischemic hearts with and without a hot shot and hypothermic cardioplegic arrest. Induction of hypothermic cardioplegia releases purines from ischemic hearts until they become cold, whereas reperfusion induces massive purine release and myocardial stunning. Inhibition of cardiac es-ENT1 nucleoside transporter abolishes postischemic reperfusion injury in warm and cold cardiac surgery.

ラット摘出心臓標本の虚血,再潅流障害におけるジルチアゼムの作用-とくに心筋プリン代謝との関係

ラット摘出心臓標本の虚血,再潅流障害におけるジルチアゼムの作用-とくに心筋プリン代謝との関係

Analysis of the myocardial metabolism by microdialysis during open beating heart surgery

Objectives. Microdialysis allows the in vivo biochemical analysis of interstitial fluids. Our aim was to reveal in vivo reliable data of the myocardium during open beating heart surgery. Design. In ten patients undergoing routine beating coronary artery bypass grafting a microdialysis catheter was inserted into the left ventricle. Measurements were performed up to 45 min after anastomosis. Data were retrospectively compared with standard on-pump procedures. Results. The myocardial lactate remained stable during anastomosis, followed by a significant decrease of lactate after revascularisation. Myocardial glucose levels showed a slight decrease, followed by a significant increase after revascularisation. Myocardial purines showed a slight increase during anastomosis, followed by a sharp decrease during reperfusion period. Conclusions. In contrast to on-pump procedures myocardial lactate and purines showed less increasing trend during the ischemic period, while myocardial glucose remained stable as a sign of preserved tissue blood flow. Myocardial microdialysis showed different values compared to the elective on-pump CABG and previous animal studies. This technique allows bedside monitoring of biochemical changes, suggesting its possible role as a clinical monitoring tool.

Aging-related changes in myocardial purine metabolism and ischemic tolerance

Impaired tolerance to ischemia-reperfusion in older hearts may stem in part from alterations in purine catabolism, impacting on maintenance of energy state and protective signaling via extracellular adenosine. We characterized effects of aging on normoxic and post-ischemic purine metabolism in hearts from young (2–4 month), middle-aged (12 month), old (18 month), and senescent (24–28 month) C57/Bl6 mice. Normoxic function was similar in all age groups while normoxic purine efflux increased gradually with age. This was the result of enhanced efflux of hypoxanthine, xanthine and uric acid, with extracellular accumulation of adenosine and inosine remaining unchanged. While total purine washout during 60 min reperfusion following 20 min global ischemia was unaltered by aging (1057±109 nmoles/g in young vs. 1221±127 nmoles/g in senescent hearts), selective changes in purine catabolism were evident. Accumulation of adenosine and inosine were reduced by 50 and 80%, respectively, matched by 400 and 300% elevations in hypoxanthine and xanthine accumulation, respectively. Uric acid remained unchanged. Thus, while adenosine and inosine represented 15±2 and 47±3% of total purine efflux in young hearts, these values decreased to only 6±1 and 9±2% in senescent hearts. Efflux of IMP also increased 500% with aging whereas 5′-AMP was unaltered. These changes were associated with a substantial fall in ischemic tolerance, with left ventricular developed pressure recovering to 46±3% in young hearts vs. only 24±6, 16±4, and 19±4% in middle-age, old and senescent hearts, respectively. Our data collectively support a pronounced shift in purine catabolism, with reduced accumulation of salvageable and cardioprotective adenosine, and enhanced accumulation of poorly salvaged (and potentially injurious) hypoxanthine and xanthine. Mechanisms underlying this shift have yet to be determined. However, this may play a role in the marked decline in myocardial tolerance to ischemia with aging and senescence.

Relationships between hemodynamic parameters and myocardial energy and antioxidant status in heart transplantation

The relationships between high-energy phosphate levels, oxidative insult and mechanical function represent a key point in heart transplantation and related post-ischemic functional recovery. We evaluated myocardial purine compounds and glutathione antioxidant defence mechanism during 19 heart transplant operations. Heart biopsies were taken before harvesting on beating heart (t1), at the end of cold static preservation (t2) and 30 min after implantation and reperfusion (t3); perchloric extracts of the tissue were analyzed by capillary electrophoresis (CE). Correlation analyses were performed with hemodynamic parameters evaluated 90 min after aortic declamping (T90), 6 h following admission in intensive care unit (T6A) and 1 d post-operation (D1). We evidenced that AMP levels measured at T1 negatively correlate with both cardiac index (CI) and oxygen delivery index (DO2I) evaluated at T6A, respectively. The same behavior was evident plotting IMP levels measured at T3 with CI and DO2I evaluated at D1. After t2 the nucleotide/(nucleoside + base) ratio was in positive correlation with hemodynamic parameters at T6A. Energy charge and GSH/GSSG ratio measured before harvesting were in positive correlation with DO2I evaluated at T90. The present research shows that despite the complexity of the high-energy phosphate metabolism and that of the events associated to a clinical heart transplantation, there are some parameters that, besides reflecting the degree of myocardial preservation, also represents predictive parameters for the following organ functional recovery. It also suggests that heart preservation strategies should carefully take into account the sub-optimal nature of the donor heart at the time of procurement, through a broad spectrum of purine compound and glutathione antioxidant system measurements.

Cardiac surgery: myocardial energy balance, antioxidant status and endothelial function after ischemia–reperfusion

Myocardial and endothelial damage is still a widely debated problem during the ischemia–reperfusion sequence in heart surgery. We evaluated myocardial purine metabolites, antioxidant defense mechanisms, oxidative status and endothelial dysfunction markers in 14 patients undergoing coronary artery by-pass graft (CABG). Heart biopsies were taken before aortic cross-clamping (t1), before clamp removal (t2) and 30 min after reperfusion (t3); perchloric extracts of the tissue were analyzed for glutathione, NAD, nucleotide nucleoside and base content by capillary electrophoresis (CE). In plasma samples from the coronary sinus we evaluated: nitrate and nitrite concentrations by CE, plasma glutathione peroxidase (plGPx) by ELISA, endothelin-1 (ET-1) by RIA and reactive oxygen metabolites (ROM) by colorimetric assay. During the ischemic period (t2) we observed a reduction in cellular NAD and GSH levels, as well as nitrate, nitrite and plGPx. ATP and GTP levels decreased and their catabolic products AMP, GMP, IMP, adenosine, inosine and hypoxanthine accumulated. The energy charge, ATP/ADP ratio, and nucleotide/(nucleoside + base) ratios decreased. At t3, levels of plasma ET-1 increased and monophosphate nucleotides tended to return to basal values. The energy charge did not increase but the nucleotide/(nucleoside + nucleobase) ratio recovered to some extent. Levels of nitrates plus nitrites continued to decrease. No significant variation in ROM levels was observed. Our data indicate that oxidative stress and endothelial damage are major events during CABG, overwhelming the scavenging capacity of the myocyte and preventing restoration of the normal energy balance for 30 min after reperfusion. The AMP deaminase pathway leading to IMP production is active during ischemia and adenosine is not the main compound derived from ATP break-down in the human heart. The possible role of extracorporeal circulation is also discussed.

Increase in myocardial interstitial adenosine and net lactate production in brain-dead pigs: an in vivo microdialysis study.

Brain death-related cardiovascular dysfunction has been documented; however, its mechanisms remain poorly understood. We investigated changes in myocardial function and metabolism in brain-dead and control pigs. Heart rate, systolic (SAP) and mean (MAP) arterial pressure, left ventricular (LV) dP/dtmax, rate-pressure product, cardiac output (CO), left anterior descending coronary artery blood flow, lactate metabolism, and interstitial myocardial purine metabolite concentrations, monitored by cardiac microdialysis, were studied. A volume expansion protocol was performed at the end of the study. After brain death, a transient increase in heart rate (from 90 [67-120] to 158 [120-200] beats/min) (median, with range in brackets), MAP (82 [74-103] to 117 [85-142] mmHg), LV dP/dtmax (1750 [1100-2100] to 5150 [4000-62,000] mmHg x sec(-1), rate-pressure product (9100 [7700-9700] beats mmHg/min to 22,750 [20,000-26,000] beats mmHg/min), CO (2.2 [2.0-4.0] to 3.3 [3.0-6.0] L/min), and a limited increase in left anterior descending coronary artery blood flow (40 [30-60] to 72 [50-85] ml/min) were observed. Net myocardial lactate production occurred (27 [4-40] to -22 [-28, -11] mg/L, P<0.05) and persisted for 2 hr. A 6-7-fold increase in adenosine dialysate concentration was observed after brain death induction (2.9 [1.0-5.8] to 15.8 [7.0-50.7] micromol/L), followed by a slow decline. Volume expansion significantly increased MAP, CO, and LV dP/dtmax in control animals, but decreased LV dP/dtmax and slightly increased CO in brain-dead animals. A significant increase in adenosine concentration was observed in both groups, with higher levels (P<0.05) in brain-dead animals. Brain death increased oxygen demand in the presence of a limited increase in coronary blood flow, resulting in net myocardial lactate production and increased interstitial adenosine concentration consistent with an imbalance between myocardial oxygen demand and supply. This may have contributed to the early impairment of cardiac function in brain-dead animals revealed by rapid volume infusion.

Myocardial ischemic injury and purine metabolism in patients undergoing coronary artery bypass.

High-energy phosphates and their catabolic products were determined in myocardium during coronary artery bypass surgery with blood cardioplegic reperfusion in order to evaluate the effects of aortic cross-clamping and reoxygenation on myocardial purine metabolism. Transmural left ventricular biopsy specimens were taken with ITu-Cut biopsy needles, before aortic cross-clamping, before cross-clamp removal and after 30' of reperfusion; perchloric extracts of the material were analyzed for nucleotide content by capillary zone electrophoresis (CZE). The CZE procedure used separates the complete spectrum of purine metabolites in myocardial extracts obtained from 0.6-8.6 mg biopsy material. The basal values of ATP/ADP ratio and energy charge were low, IMP content was high. After the ischemic period, ATP levels further decreased and IMP, nucleosides and bases accumulated. After reperfusion, nucleoside and base basal levels, but not energy charge, were restored to some extent. The study arises the problem of myocardial preservation during heart surgery. In this investigation, capillary electrophoresis was an extremely adaptable technique for the evaluation of ischemic injury and could be useful in studying the effects of cardioplegic solutions.

Metabolic supplementation with orotic acid and magnesium orotate.

Orotic acid (OA), a naturally occurring substance, is a key intermediate in the biosynthetic pathway of pyrimidines. Previous investigations in the heart suggest that orotate can protect recently infarcted hearts against a further ischemic stress and may be beneficial in certain types of experimental cardiomyopathy. At the Hamburg symposium on magnesium orotate, a number of studies of this form of metabolic supplementation were presented that indicate orotic acid and its magnesium salt have a modest beneficial effect on the myocardium under conditions of stress ranging from myocardial infarction to severe physical exercise. The following conclusions can be drawn: (1) Orotic acid can improve the energy status of the recently infarcted myocardium (rat hearts). (2) Orotic acid may improve myocardial purine and pyrimidine levels by stimulating hepatic release of uridine into the bloodstream, which in turn augments depleted myocardial pyrimidines and purines (rat heart). (3) Orotic acid improves the tolerance of the recently infarcted heart to global ischemia (rats). (4) Magnesium orotate may reduce the severity of chronic myocardial dysfunction and structural damage in cardiomyopathy (cardiomyopathic hamsters). (5) Magnesium orotate may improve exercise tolerance in patients with coronary artery disease and in trained athletes (humans). (6) Magnesium orotate has only a weak inotropic effect, if any, on normal hearts (rats). (7) Further clinical testing is indicated to determine if the effects described could be of significant clinical benefit in the treatment of heart disease.

Integration of vascular, contractile and metabolic responses to hypoxia: effects of maturation and adenosine.

We examined myocardial responses to reduced arterial PO2 and the role of endogenous adenosine in constant-pressure perfused hearts from immature (Imm) and mature (Mat) rabbits. During normoxia, coronary flow and myocardial O2 consumption were similar in both groups. With moderate hypoxia, coronary perfusate flow increased by 125 +/- 16% in Imm but by only 68 +/- 12% in Mat hearts. Imm hearts displayed better maintenance of contractile function (87 vs. 67% in Mat hearts) and metabolic state. Blockade of cardiac adenosine receptors with 25 microM 8-p-sulfophenyltheophylline attenuated vasodilation during hypoxia, reduced contractile function, and abolished age-related differences in one response to hypoxia. Myocardial purine release and extracellular purine levels were threefold higher in Mat compared with Imm hearts and was associated with higher cytosolic 5'-AMP concentration (and lower [ATP]/[ADP].[P(i)], where [ATP], [ADP], and [P(i)] are concentrations of ATP, ADP and P(i), respectively) in Mat hearts. In summary, 1) Imm hearts are functionally and metabolically more tolerant of hypoxic perfusion, largely because of improved hypoxia-induced coronary vasodilation; 2) endogenous adenosine mediates this beneficial vasodilation, enhancing hypoxic tolerance; and 3) improved vascular sensitivity to adenosine allows for enhanced vasodilatory responses in the face of lower adenosine levels and higher energy state in immature hearts.

Myocardial interstitial purine metabolites and lactate with increased work in swine

Myocardial interstitial purine metabolites and lactate with increased work in swine

Nicorandil suppressed myocardial purine metabolism during exercise in patients with angina pectoris.

To elucidate the effect of Nicorandil on myocardial energy metabolism and myocardial sympathetic activity, we administered Nicorandil orally to eight patients with angina pectoris prior to exercise testing. Arterial and coronary sinus levels of lactate, ammonia, hypoxanthine (HX), adrenaline and noradrenaline were measured during exercise in order to determine the irrespective myocardial extraction ratios (MER). Compared to placebo, Nicorandil increased the time to development of significant ST depression (322 vs 390 s) while decreasing the maximum amplitude of ST depression (0.244 vs 0.216 mV). Heart rate, systolic blood pressure, and the rate pressure product during exercise were not significantly affected. The MER of lactate, measured during exercise, was significantly higher after Nicorandil than placebo (13.6 vs 27.9). Similarly, the MERs of ammonia and HX were significantly higher after Nicorandil (-46.0 vs 7.4% and -47.0 vs 9.9% respectively). Nicorandil, had no apparent effect on myocardial sympathetic activity as the MERs of adrenaline and noradrenaline were essentially unaffected. We conclude that Nicorandil decreased myocardial ischaemia and suppressed myocardial accelerated purine metabolism (a marker of cellular energy metabolism) during exercise in patients with angina pectoris. This effect appears not to be related to myocardial sympathetic activity.

Does the Severity of Acute Hypoxia Influence Neonatal Myocardial Metabolism and Sensitivity to Ischemia?

The level of systemic hypoxia required to alter neonatal myocardial metabolism and its resultant effect on tolerance to global ischemia is unknown. This study examines myocardial purine nucleotides, glycogen (MG), lactate, creatine phosphate (CP) and the subsequent tolerance to ischemia in hearts exposed to varying levels of hypoxia (2 h). Three-day-old swine were randomly allocated into five study groups. Animals were anaesthetized and ventilated (2 h) with varying mixtures of medical air and nitrogen to achieve their target PaO 2 (mmHg); normoxia (PaO 2 = 80, n = 18), mild (PaO 2 = 60, n = 10), moderate (PaO 2 = 40, n = 12), moderately-severe (PaO 2 = 30, n = 7) and severe (PaO 2 = 20, n = 9). Arterial blood gases verified PaO 2 and normal PaCO 2 (39.5 ± 0.5 mmHg). Subsequently, the heart was exposed and the metabolic profile determined from a freeze-clamp LV biopsy. The heart was excised and tolerance to ischemia determined by time (min) to ischemic contracture onset (TICo) and peak (TICp). The results demonstrated a tendency to decreased MG with progressive hypoxia which reached significance in severe hypoxia (6.6 ± 2.7 μmol/g. P <0.05). Despite a doubling of myocardial lactate with moderately-severe hypoxia, increases only reached significance with severe hypoxia (27.8 ± 6.3 μmol/g, P<0.0001). Despite the reduction in LV adenosine triphosphate (ATP) with severe hypoxia (2.16 ± 0.68 μmol/g, P<0.05). CP was unaltered. The slightly (13%) depressed ischemic tolerance with all levels of hypoxia only reached significance with severe hypoxia (TICo = 11.3 ± 2.2 P<0.0001 and TICp = 27.4 ± 3.1, P<0.05). From normoxia to moderately-severe hypoxia (2 h), neonatal myocardial metabolism and tolerance to ischemia were not significantly altered. With a slight further PaO 2, reduction, hearts had significantly altered metabolism and decreased ischemic tolerance.

Physiology of cardiovascular aging

Physiology of cardiovascular aging

Effect of allopurinol on myocardial purine release after total ischaemia in isolated rat heart.

Effect of allopurinol on myocardial purine release after total ischaemia in isolated rat heart.

Effects of nucleoside transport inhibition on long-term ex vivo preservation of canine hearts

The effect of nucleoside transport inhibition on 24-hour preservation of canine hearts was studied in 36 hearts arrested either with a cold hyperkalemic cardioplegic solution without (group I) or with supplementation of a specific nucleoside transport inhibitor (R75231, 1 mg/L) (groups II and III). The hearts were excised and stored for 24 hours at 0.5 degrees C. Then they were reperfused for 3 hours with use of a closed perfusion system primed with normal blood (groups I and II) or with blood supplemented with the same nucleoside transport inhibitor (0.32 mg/L) (group III). Serial biopsy specimens for determination of myocardial purines were taken. Creatine kinase and heat-stable lactate dehydrogenase release from the myocardium were examined during reperfusion. Recovery of function was studied during reperfusion by measurement of isometric contraction in a fluid-filled intraventricular balloon. After 24 hours of preservation, without the use of the drug, myocardial inosine and hypoxanthine accumulated to, respectively, 4.05 +/- 1.18 and 0.28 +/- 0.08 mumol/gm dry weight. In the drug-treated groups (II and III pooled), significantly less inosine and hypoxanthine accumulated (1.68 +/- 0.33 and 0.05 +/- 0.02 mumol/gm dry weight, respectively) (p < 0.05 versus group I). Upon reperfusion, intramyocardial adenosine was lost in the control hearts and maintained in the drug-treated hearts. Hypoxanthine accumulated significantly (p < 0.05) during reperfusion in group I (1.08 +/- 0.43 versus 0.16 +/- 0.13 in group II and 0.03 +/- 0.03 mumol/gm dry weight in group III). The rate of creatine kinase and heat-stable lactate dehydrogenase release was significantly lower (p < 0.05) in group III (that is, pretreatment and posttreatment with the drug) than in the control group. Functional recovery of hearts in group III was superior to that in group II (p < 0.05), while hearts in group I showed no recovery at all. We conclude that nucleoside transport inhibition improves long-term preservation of the heart and that the mechanism of this protection may be related to an increase in endogenous adenosine and reduction of myocardial hypoxanthine content.

Relation between coronary artery stenosis and myocardial purine metabolism, histology and regional function in humans

In 54 patients undergoing elective or emergency aortocoronary bypass grafting, angiographic and electrocardiographic changes were studied. Five patients with unstable angina and five patients with evolving myocardial infarction 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 partial depletion of the adenylate pool. Mitochondrial function, however, remained intact: the adenosine diphosphate/adenosine triphosphate ratio, the energy charge and the creatine phosphate/adenosine triphosphate ratio were in the normal range. Histologic assessment demonstrated viable myocardium with a high incidence of atrophic cells. In evolving myocardial infarction, 170 minutes of acute coronary artery obstruction resulted in anterior wall akinesia associated with a decrease of the sum of the adenylates to 52% and of creatine phosphate to 16% of their normal value (p less than 0.05). The nucleosides accumulated; their major fraction (91%) was inosine. The adenosine diphosphate/adenosine triphosphate ratio increased from 0.14 +/- 0.04 to 0.49 +/- 0.20 (p less than 0.01) and the energy charge decreased from 0.924 +/- 0.021 to 0.660 +/- 0.169 (p less than 0.01). Ultrastructure examination revealed irreversible cell damage in at least the subendocardial layer. These results suggest that the energetic base of reduced contractility due to severe coronary artery stenosis is different from that in acute coronary obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental differences in myocardial ATP metabolism.

Little is known about postnatal changes in myocardial purine metabolism. We therefore studied how ATP catabolism was affected by hypothermia and ischaemia in neonatal and adult hearts. Hypothermia during ischaemia protected isolated adult and newborn hearts against ATP decline. Reperfusion after normothermic ischaemia resulted in higher ATP levels in newborn hearts with less release of ATP-catabolites. During normoxia adult hearts released mainly urate (80% of total purine release), while newborns released mainly hypoxanthine (64%). During early reperfusion adult and newborn hearts released mainly inosine (50-60%). The very low xanthine oxidase activity in the neonatal heart could be an important factor in the observed ATP preservation during reperfusion.

Purine nucleotides in human hearts during open heart surgery.

During open heart surgery aortic clamping is the reason of a temporary deficiency in oxygen supply and the development of ischemia. Hypothermia and cardioplegia should protect the myocardium against an irreversible injury. As an effect of ischemia myocardial content of high-energy phosphates decreases which is accompanied by the release of degradation products (1, 2). In order to evaluate myocardial purine nucleotide metabolism tissue samples were taken during open heart surgery and the concentrations of purine necleotides were determined using isotachophoresis.KeywordsPyruvate KinaseAdenine NucleotideOpen Heart SurgeryPurine NucleotideCardioplegic SolutionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Adenosine deaminase inhibition and myocardial purine release during normoxia and ischaemia.

Quantitative determination of myocardial adenosine formation and breakdown is necessary to gain insight into the mechanism and regulation of its physiological actions. Deamination of adenosine was studied in isolated perfused rat hearts by infusion of adenosine (1 to 20 mumol X litre-1). All catabolites in the perfusates (inosine, hypoxanthine, xanthine and uric acid) were measured, as well as unchanged adenosine. Apparent uptake of adenosine was determined; it increased linearly with the concentration of adenosine infused. Adenosine was predominantly deaminated, even at low (1 mumol X litre-1) concentration. The inhibitory capacity of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) was determined, while 5 mumol X litre-1 adenosine was infused. EHNA inhibited the apparent adenosine deaminase activity for 62 and 92% at 5 and 50 mumol X litre-1, respectively. When 50 mumol X litre-1 EHNA was infused into normoxic hearts, release of adenosine was significantly elevated, as was coronary flow. Induction of ischaemia increased total purine release four-to fivefold. Infusion of EHNA into ischaemic hearts did not alter total purine release, but adenosine release increased from 15 to 60% of total purines. However, when EHNA was present, a large part of total purine release still existed of inosine, hypoxanthine, xanthiner and uric acid. This was 83% during normoxia and 40% during ischaemia. These results suggest significant contribution of IMP and GMP breakdown to purine release from isolated perfused rat hearts.