Ischemia In Isolated Rat Heart Research Articles

Myocardial protection from ischemia/reperfusion injury by exogenous galanin fragment.

Background and purposeGalanin is a multifunctional neuropeptide with pleiotropic roles. The present study was designed to evaluate the potential effects of galanin (2-11) (G1) on functional and metabolic abnormalities in response to myocardial ischemia-reperfusion (I/R) injury.Experimental approachPeptide G1 was synthesized by the 9-fluorenylmethoxycarbonyl (Fmoc)-based solid-phase method. The chemical structure was identified by 1H-NMR spectroscopy and mass spectrometry. Experiments were conducted using a rat model of I/R injury in vivo, isolated perfused rat hearts ex vivo and cultured rat cardiomyoblast H9C2 cells in vitro. Cardiac function, infarct size, myocardial energy metabolism, hemodynamic parameters, plasma levels of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) were measured in order to evaluate the effects of G1 on myocardial I/R injury.Key resultsTreatment with G1 increased cell viability in a dose-dependent manner, inhibited cell apoptosis and excessive mitochondrial reactive oxygen species (ROS) production in response to oxidative stress in H9C2 cells. Pre- or postischemic infusion of G1 enhanced functional and metabolic recovery during reperfusion of the ischemic isolated rat heart. Administration of G1 at the onset of reperfusion significantly reduced infarct size and plasma levels of CK-MB and LDH in rats subjected to myocardial I/R injury.Conclusions and implicationsThese data provide the first evidence for cardioprotective activity of galanin G1 against myocardial I/R injury. Therefore, peptide G1 may represent a promising treatment strategy for ischemic heart disease.

Resistance to reperfusion injury following short term postischemic administration of natural honey in globally ischemic isolated rat heart.

RESULTS of our previous study revealed that preischemic perfusion of honey before zero flow global ischemia had cardioprotective effects in rat. The present study investigated potential resistance to reperfusion injury following short term postischemic administration of natural honey in globally ischemic isolated rat heart. Male Wistar rats were divided into five groups (n=10-13). The rat hearts were isolated, mounted on a Langendorff apparatus, allowed to equilibrate for 30 min then subjected to 30 min global ischemia. In the control group, the hearts were reperfused with drug free normal Krebs-Henseleit (K/H) solution before ischemia and during 120 min reperfusion. In the treatment groups, reperfusion was initiated with K/H solution containing different concentration of honey (0.25, 0.5, 1 and 2%) for 15 min and was resumed until the end of 120 min with normal K/H solution. In the control group, VEBs number was 784±199, while in honey concentration of 0.25, 0.5, 1 and 2%, it decreased to 83±23 (P<0.001), 138±48 (P<0.01), 142±37 (P<0.001) and 157±40 (P<0.01), respectively. Number and duration of VT and time spent in reversible VF were also reduced by honey. In the control group, the infarct size was 54.1±7.8%, however; honey (0.25, 0.5, 1 and 2%) markedly lowered the value to 12.4±2.4, 12.7±3.3, 11.3±2.6 and 7.9±1.7 (P<0.001), respectively. Postischemic administration of natural honey in global ischemia showed protective effects against ischemia/reperfusion (I/R) injuries in isolated rat heart. Antioxidant and radical scavenging activity, lipoperoxidation inhibition, reduction of necrotized tissue, presence of rich energy sources, various type of vitamins, minerals and enzymes and formation of NO-contain metabolites may probably involve in those cardioprotective effects.

Improved functional recovery by ischaemic preconditioning is not mediated by adenosine in the globally ischaemic isolated rat heart.

Improved functional recovery by ischaemic preconditioning is not mediated by adenosine in the globally ischaemic isolated rat heart.

Effects of an Angiotensin II Antagonist on Ischemic and Nonischemic Isolated Rat Hearts

Background. Increasing evidence suggests that a locally integrated or intramyocardial renin-angiotensin system plays a significant role in ischemia-reperfusion injury. We evaluated the effects of losartan, an angiotensin II type 1 receptor blocking agent, on ischemic and nonischemic isolated rat hearts. Methods. Using the modified Langendorff model, hearts were perfused with either low or high doses of losartan (18.2 mmol/L or 182.2 mmol/L, respectively) or with saline added to Krebs-Henseleit solution during phase I of the study. During phase II, hearts were exposed to a 60-minute period of global ischemia. Ischemic arrest was induced with warm cardioplegic solution (KCl, 16 mEq/L) containing either high-dose losartan (182.2 mmol/L) or Krebs-Henseleit solution only. Results. During phase I of the study, no statistically significant differences were observed between the low-dose losartan group and the control group. However, hearts treated with high-dose losartan demonstrated an increase in peak systolic pressure, maximum first derivative of pressure, pressure-time integral, coronary flow, and oxygen consumption ( p < 0.0001). During phase II, hearts treated with losartan showed a significantly better recovery on reperfusion, as reflected by better contractility ( p < 0.001), higher oxygen consumption ( p < 0.001), higher coronary flow ( p < 0.0001), and lower creatine phosphokinase levels (41.1 ± 1.7 versus 73.3 ± 5.6 U/L; p < 0.001). Conclusions. High doses of losartan have a positive inotropic effect on normally perfused hearts. Given in cardioplegic solution, the drug has a significant protective effect on ischemic isolated rat hearts.

Electron paramagnetic resonance imaging of rat heart with nitroxide and polynitroxyl-albumin.

Electron paramagnetic resonance (EPR) imaging utilizing stable nitroxyl radicals is a promising technique for measuring free radical distribution, metabolism, and tissue oxygenation in organs and tissues [Kuppusamy, P., Chzhan, M., Vij, K., Shteynbuk, M., Lefer, D. J., Giannella, E., & Zweier, J. L. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 3388-3392]. However, the technique has been limited by the rapid reduction of nitroxide in vivo to its hydroxylamine derivative, a diamagnetic, EPR-inactive species. In this report a novel, polynitroxylated derivative of human serum albumin is shown to be capable of reoxidizing the hydroxylamine back to nitroxide in vivo. Polynitroxyl-albumin (PNA) is shown to be effective in maintaining the signal intensity of the nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL or TPL) in the ischemic isolated rat heart, allowing the acquisition of high-resolution three-dimensional (3D) EPR images of the heart throughout a prolonged 2.5 h period of global cardiac ischemia. In serial transverse sections of the 3D image, TPL intensity maps of the heart showed cardiac structure with submillimeter resolution. TPL intensities in coronary arteries and myocardium showed that nitroxide concentration decreases with increasing distance from large blood vessels. These results demonstrate that EPR imaging in vivo is possible using nitroxides in conjunction with PNA. In addition to its utility in the emerging technology of EPR imaging, the greatly prolonged half-life of TPL observed in the presence of PNA may facilitate the therapeutic application of nitroxides in a variety of disease processes.

Antiarrhythmic effects of ceruloplasmin during reperfusion in the ischemic isolated rat heart.

The ability of ceruloplasmin, an important serum antioxidant, to reduce the vulnerability of the isolated rat heart to reperfusion arrhythmias has been investigated. Bovine plasma ceruloplasmin was purified by chromatography on aminoethyl-agarose. Isolated rat hearts were submitted to 15 min of regional ischemia and 10 min of reperfusion. The dose-effect relationship and the role of ceruloplasmin conformational integrity in cardioprotection were established by treatment of ischemic hearts with ceruloplasmin at various concentrations (0.25, 0.5, 1, and 2 microM) and at different degrees of conformational integrity (A610/A280 = 0.02, 0.04, and 0.06), 5 min before reperfusion. Deferoxamine (20-500 microM) was used as a positive control. As negative controls we used chemically inactivated ceruloplasmin (1 microM), heat-denatured ceruloplasmin (1 microM), and albumin (1-4 microM). In the control group during the first 5 min of reperfusion, the incidence of total ventricular fibrillation was 100% and of irreversible ventricular fibrillation was 83%. The incidence of reversible and irreversible ventricular fibrillation was significantly decreased in the ceruloplasmin-treated groups in both a dose and molecular integrity dependent manner. Ceruloplasmin had no effect on the incidence of ventricular tachycardia. Deferoxamine reduced the incidence of ventricular fibrillation to the same degree as ceruloplasmin but at concentrations much higher than those of ceruloplasmin. Chemically inactivated ceruloplasmin, heat-denatured ceruloplasmin, and albumin had no protective effects on reperfusion-induced arrhythmias.

Nitrous oxide does not depress left ventricular contractility in ischemic rat heart

The direct effects of nitrous oxide on left ventricular contractility and myocardial oxygen consumption (MVO2) in the ischemic isolated rat heart were studied. The rat heart was isolated and perfused by a Langendorf technique. The aortic stump was cannulated and the heart was perfused with Kumpeis solution bubbled with 95% O2 and 5% CO2 (control phase). A latex balloon was inserted into the left ventricle (LV) to measure LV pressures and dP/dt. Coronary flow was measured and MVO2 was calculated. After the control phase, perfusion pressure was decreased to induce global ischemia (ischemic phase). There were four groups of eight hearts each: control, nitrogen, nitrous oxide, and halothane groups. After 15 min of ischemic phase, the perfusion pressure was increased and the gas mixture was changed to the standard gas mixture (reperfusion phase). Nitrous oxide did not further depress myocardial contractility compared with nitrogen in the ischemic phase, and did not alter MVO2 in the ischemic phase compared with nitrogen. Halothane significantly depressed myocardial contractility and decreased MVO2 in the ischemic phase compared with the control.

Adenosine and the stunned heart.

Adenosine is one agent under investigation as a therapeutic intervention of myocardial stunning. Adenosine caused numerous effects on the cardiovascular system through its interaction with A1 and A2 receptors. We investigated adenosine A1 receptor mediated mechanisms of cardiac protection in the stunned rat myocardium. Previous studies showed that both adenosine and R-phenylisopropyladenosine (PIA), an A1 receptor agonist, prolonged the time to onset of ischemic contracture in ischemic isolated rat hearts. Phenylaminoadenosine, an A2 receptor agonist, did not have any effect, while receptor antagonists blocked adenosine and PIA action. Direct attenuation of the effects of myocardial stunning was observed by altering levels of interstitial fluid adenosine. Our laboratory has shown that administration of erythro-9(2-hydroxy-3-nonyl) adenine (EHNA; an adenosine deaminase inhibitor) to dogs subjected to left anterior descending coronary artery (LAD) occlusion followed by reperfusion results in dramatic increases in ischemic levels of interstitial fluid adenosine and postischemic myocardial function. Using a similar model in dogs, we have shown that exogenous intracoronary adenosine (50 micrograms/kg per min) augmented postischemic recovery of function, as assessed by significant enhancement (p < 0.01) of systolic wall thickness (7.0 +/- 3.0 pretreatment vs -5.7 +/- 1.7 controls). These data support the role for an adenosine A1 receptor mediated mechanism for protection against myocardial stunning.

Adenosine fails to substitute for preconditioning in the globally ischemic isolated rat heart

Adenosine fails to substitute for preconditioning in the globally ischemic isolated rat heart

Protection of the Reperfused Ischemic Isolated Rat Heart by Phosphatidylcholine

We examined phosphatidylcholine (PC) effects on the isolated rat heart subjected to low- or zero-flow ischemia followed by reperfusion. Untreated hearts subjected to 30 min of low-flow ischemia recovered 15% contractility following reperfusion compared to time-control hearts. Phosphatidylcholine (0.005%) addition either 10 or 20 min before ischemia significantly enhanced recovery to approximately 61% and reduced the incidence of arrhythmias during ischemia and reperfusion. Contracture during ischemia and reperfusion was significantly reduced when PC was added 20 min before ischemia. Phosphatidylcholine was ineffective when administered at the time of reperfusion except for a moderate reduction in arrhythmia development. Phosphatidylcholine also produced a salutary effect when added 20 min prior to zero-flow ischemia. Subsarcolemmal mitochondria (SLM) and, to a much lesser degree, interfibrillar mitochondria (IFM) of untreated hearts subjected to low-flow ischemia and reperfusion exhibited depressed oxidative phosphorylation which was prevented by PC. Both mitochondrial populations exhibited a marked depression in ADP/ATP translocase activity; however, this was generally unaffected by PC. Subsarcolemmal mitochondria but not IFM of zero-flow ischemic reperfused hearts also exhibited significantly depressed oxidative phosphorylation, which was unaffected by PC. Zero-flow ischemia produced a rapid and total cessation of contractility. Both populations exhibited a substantial PC-insensitive reduction in translocase activity. Our results demonstrate, for the first time, a protection by PC on the reperfused ischemic heart. The PC-induced protection following low-flow but not zero-flow ischemia is associated with improved SLM oxidative phosphorylation suggesting dissimilar contribution of mitochondria to reperfusion-associated myocardial injury.

Adenosine A1 receptor mediated protection of the globally ischemic isolated rat heart

The purpose of this study was to determine if the cardioprotective effect of adenosine on the ischemic myocardium is mediated by interaction with specific adenosine receptor subtypes. Isolated rat hearts perfused at constant flow were subjected to global normothermic (37°C) ischemia and the time to onset of ischemic contracture (TOIC) was used as a marker of myocardial ischemic injury. Hearts treated with adenosine and R-phenylisopropyladenosine (PIA), an adenosine A 1 receptor agonist, exhibited a significantly greater TOIC than control hearts (18.60 ± 0.40 and 16.64 ± 1.15 min, respectively vs 9.12 ± 0.66 min), whereas phenylaminoadenosine, an adenosine A 2 receptor agonist, had no effect on TOIC (11.73 ± 0.87 min). BW A1433U, an adenosine receptor antagonist, blocked the effects of adenosine and PIA on ischemic contracture time, and BW A1433U did not alter the ability of nifedipine or propranolol to delay the onset of ischemic contracture, thus indicating the specificity of this compound for the adenosine receptor. PIA-treated hearts exhibited significantly greater ATP levels throughout the ischemic period compared to control hearts, whereas hearts treated with BW A1433U showed a rapid decline in ATP content. These results suggest that the beneficial effects of adenosine on the ischemic myocardium are mediated by interaction with adenosine A 1 receptors, and that endogenously formed adenosine plays a role in attenuating myocardial ischemic damage.

Relationship between oxidative phosphorylation and adenine nucleotide translocase activity of two populations of cardiac mitochondria and mechanical recovery of ischemic hearts following reperfusion

The possible relationship of the atractyloside-sensitive adenine nucleotide translocase activity, oxidative phosphorylation, and the recovery of ventricular contractility following reperfusion of the ischemic isolated rat heart was studied. Five minutes of total global ischemia without reperfusion produced a significant depression in adenine nucleotide translocase in subsarcolemmal mitochondria (SLM), whereas a minimum of 10 min ischemia was required to observe a significant depression in interfibrillar mitochondria (IFM). Increasing durations of ischemia resulted in a progressively larger depression in translocase activity, with a maximum depression of approximately 75% seen in both populations following 20 min ischemia. In contrast, oxidative phosphorylation was totally unaffected in either mitochondrial population following up to 20 min of ischemia. We assessed whether translocase activity or oxidative phosphorylation were related to contractile recovery in hearts reperfused following various durations of ischemia. In SLM, translocase activity was further depressed following reperfusion compared with pre-reperfusion ischemic values, whereas with IFM only reperfusion following 5 min ischemia produced a further depression in translocase values. Oxidative phosphorylation rates of SLM and IFM were significantly depressed following reperfusion of ischemic hearts, although SLM exhibited a generally higher sensitivity in this regard. In reperfused hearts, an overall significant relationship was found between oxidative phosphorylation rate and adenine translocase activity as well as between translocase activity and post-reperfusion contractile recovery. These data show that ischemia can produce a significant depression in translocase activity in the absence of any change in oxidative phosphorylation. The results also suggest that the depression in mitochondrial ADP/ATP translocase and subsequent inhibition of oxidative phosphorylation in the reperfused heart may represent one of the important contributory mechanisms involved in cardiac failure and injury during acute ischemia and reperfusion.

Regional myocardial flow following reperfusion of the ischemic isolated rat heart: Johansson M, Abrahamsson T and Sjöqvist PO. Dept of Cardiovasc. Pharmacol. Hässle Res. Labs. Mölndal, Sweden

Regional myocardial flow following reperfusion of the ischemic isolated rat heart: Johansson M, Abrahamsson T and Sjöqvist PO. Dept of Cardiovasc. Pharmacol. Hässle Res. Labs. Mölndal, Sweden

Direct effects of furosemide and amiloride on the perfused and ischaemic rat heart.

The present study was undertaken in order to assess direct effects of furosemide and furosemide plus amiloride upon the perfused and ischaemic isolated rat heart. Furosemide in concentrations ranging between 4-400 mg/l in the perfusate increased coronary flow in a concentration dependent manner. There was no evidence for a negative inotropic effect of furosemide. However, very high doses of furosemide (400 mg/l) decreased the post-ischaemic values of left ventricular developed pressure, coronary flow rate, adenosine triphosphate, creatine phosphate and potassium, and increased the myocardial content of calcium and sodium. Furosemide 4 mg/l and 40 mg/l had no effect on post-ischaemic parameters compared to the control group except that furosemide 40 mg/l increased the recovery of coronary flow. Although amiloride 13.3 mg/l alone did not affect post-ischaemic recovery, the addition of this dose to furosemide 400 mg/l improved the post-ischaemic recovery of left ventricular developed pressure, coronary flow rate and adenosine triphosphate. The myocardial content of magnesium and potassium was higher indicating protection of amiloride by its magnesium- and potassium-sparing properties opposing ischaemic losses aggravated by the exposure to furosemide.

Captopril improves recovery of adenosine triphosphate during reperfusion of the ischemic isolated rat heart; a 31-phosphorus-nuclear magnetic resonance study.

The effect of captopril on energy-rich phosphates and pH during normothermic ischemic arrest, hypothermic cardioplegic arrest and subsequent reperfusion was investigated in the isolated rat heart using 31P-nuclear magnetic resonance. The hearts remained in the probe during all perfusion procedures and captopril (80 ml.l-1) treatment was started directly after cannulation. After normothermic ischemic arrest (15 min), the ATP content of captopril-treated hearts was not significantly different from that of untreated hearts (53 +/- 9% and 52 +/- 8%, respectively). Accumulation of inorganic phosphate at the end of ischemia was significantly less in treated hearts, suggesting a higher end-ischemic nucleotide content in treated hearts. Hypothermic cardioplegic arrest (St. Thomas' Hospital solution, 4 degrees C) lasted for 3 h at 10 degrees C. Adenosine triphosphate in untreated hearts was significantly lower at the end of ischemia; 36 +/- 6% compared to 53 +/- 9% for untreated hearts. Adenosine triphosphate in untreated hearts recovered to 76 +/- 9% after normothermic ischemia and to 72 +/- 7% after hypothermic ischemia at the end of 30 min reperfusion. Captopril significantly improved adenosine triphosphate recovery in both treated groups; 89 +/- 4% after normothermic and 83 +/- 4% hypothermic ischemia. We conclude that captopril has a beneficial effect on recovery of adenosine triphosphate both after normothermic and after hypothermic ischemia.

Origins of endogenous noradrenaline overflow during reperfusion of the ischaemic rat heart.

1. Reperfusion of the globally ischaemic isolated rat heart is associated with an enhanced overflow of endogenous noradrenaline (NA) after ischaemic periods of 20, 40 or 60 min but not of 10 min. 2. Reperfusion NA overflow, after 40 min of ischaemia, is suppressed by desipramine and increased when ischaemia follows a period of substrate deprivation. 3. Reperfusion after 40 min of ischaemia is associated with a significant rise in NA concentration despite a simultaneous 20-fold increase in flow. This increase in concentration is abolished by treatment with desipramine or if ischaemia follows a period of substrate deprivation. 4. Reperfusion NA overflow correlates with the reperfusion overflow of an extracellular space marker infused before the ischaemic episode. 5. These results suggest that ischaemia is heterogeneous and that NA is released into regions of particularly profound ischaemia from which it is subsequently eluted during reperfusion.

Influence of Local Converting Enzyme Inhibition on Angiotensin and Bradykinin Effects in Ischemic Rat Hearts

To investigate the influence of local cardiac converting enzyme (CE) inhibition on the effects of angiotensin I (ANG I), ANG II, and bradykinin (BK), experiments were performed in ischemic isolated perfused working rat hearts. Acute regional myocardial ischemia was induced by 15 min occlusion of the left coronary artery followed by reperfusion. In ischemic isolated rat hearts, perfusion with ramiprilat (100 ng/ml, 2.58 x 10(-7) mol/l), the active moiety of the CE inhibitor ramipril, after coronary occlusion protected against ventricular fibrillation that invariably occurred in untreated control hearts in the reperfusion period. Addition of ANG I and ANG II to the perfusate enhanced, whereas BK reduced postischemic reperfusion arrhythmias, which were almost abolished in the hearts from ramipril (1 mg/kg p.o.) pretreated rats. Perfusion with ANG I and ANG II reduced cardiac function and coronary flow, increased the activities of lactate dehydrogenase and creatine kinase in the perfusate, and decreased high-energy-rich phosphates and glycogen in the myocardium. In contrast, BK reduced the enzymatic activities in the perfusate and improved the metabolic parameters in the myocardium. In hearts from ramipril pretreated animals, the ANG I effects were abolished, whereas the ANG II actions remained unchanged. The results of these experiments are consistent with the hypothesis that the beneficial effects of CE inhibitors on ventricular arrhythmias, cardiac function, and metabolism are due to local interference with CE in the coronary vascular wall or heart tissue and subsequent reduction of local ANG II generation and BK degradation.

Evaluation by 31P NMR of the effects of acebutolol on the ischaemic isolated rat heart

We used 31P NMR spectroscopy to study the effect of acebutolol on the metabolic disturbances caused by ischaemia in the isolated rat heart. The intracellular acidosis and high-energy phosphate compound depletion induced by global low-flow ischaemia were significantly attenuated in the presence of acebutolol 2.7 × 10 −5 and 1.35 × 10 −4 M. The drug displayed no significant effect either at the 5.4 × 10 −6 M concentration or when administered as pretreatment to the animals (50 mg × kg −1, 120 and 60 min before isolating the heart). Since acebutolol had no effect on the contractility of the isolated rat heart at the 2.7 × 10 −5 M concentration the present results suggest that the mechanisms through which acebutolol exerts its effects on energy metabolism are not related to a reduction of cardiac work. The possible contribution of the membrane-stabilizing property of the drug is suggested by the fact that high concentrations are needed and that a short pretreatment had no effect.

Beneficial Effects of the Converting Enzyme Inhibitor, Ramipril, in Ischemic Rat Hearts

Components of the renin-angiotensin system (RAS) have been found in heart tissue and it is likely that angiotensin II (ANG II) is generated locally in the heart as in other organs. Pharmacological interference with converting enzyme (CE) inhibitors reduced CE activity and ANG II generation in the heart. To investigate whether local inhibition of CE in the heart with the CE inhibitor ramipril might contribute to the therapeutic effects, experiments were performed in isolated perfused working rat hearts. Acute regional myocardial ischemia was induced by occlusion of the left coronary artery followed by reperfusion. In ischemic isolated rat hearts, both single oral pretreatment with ramipril (1 mg/kg) or perfusion with the active moiety, ramiprilat (10 micrograms/ml), protected against ventricular fibrillation, which invariably occurred in control hearts during reperfusion. Reperfusion arrhythmias were aggravated by perfusion with ANG I and ANG II, but prevented by bradykinin. ANG I-enhanced ventricular fibrillations were completely eliminated during local CE inhibition with ramipril. The CE inhibitor also improved cardiodynamics. Coronary flow, left ventricular pressure, dp/dtmax, and myocardial oxygen consumption were increased in comparison to controls without changes in heart rate. In the perfusate of treated hearts, lactate dehydrogenase, and creatine kinase activities and lactate production, were reduced. Myocardial tissue levels of glycogen, ATP, and creatine phosphate were increased in ramipril-pretreated hearts whereas lactate was decreased. The results of these experiments in rat hearts suggest that local inhibition of CE by ramipril exerts protective effects after ischemia and reperfusion by reducing arrhythmias and improving cardiac function and metabolism, thus probably contributing to the therapeutic effects of CE inhibitors in cardiovascular diseases.

Ischaemic contracture in isolated rat heart: reversible or irreversible myocardial injury?

An isolated rat heart preparation was reperfused at 37 degrees C for 10 min after 10, 20, 30 and 40 min of ischaemia. The left ventricular tension was measured by means of a balloon catheter filled with water and connected to a pressure recorder. The left ventricular resting tension began to increase at 9 +/- 1 min (mean +/- SEM) and was maximally developed (myocardial contracture) at 18 +/- 1 min of ischaemia. There was a striking and constant exacerbation of the resting tension during reperfusion after 30 and 40 min (but not after 10 or 20 min) of ischaemia with simultaneous acceleration of creatine phosphokinase (CK) release into the coronary effluent and with the loss of the recovery of contractile activity. Myocardial adenosine triphosphate (ATP)-content decreased during 20 min of ischaemia more in the endocardial (ENDO) (from 17.7 +/- 1.9 mumol/g to 0.7 +/- 0.1 mumol/g) than in epicardial (EPI) (from 15.5 +/- 0.9 mumol/g to 3.2 +/- 0.6 mumol/g) parts of myocardium. Reperfusion after 10 min of ischaemia resulted in a slight increase of myocardial ATP-content both in EPI (from 7.5 +/- 0.6 to 10.4 +/- 0.8 mumol/g, p less than 0.05) and ENDO (from 5.0 +/- 0.8 to 8.9 +/- 2.5 mumol/g, n.s.). Reperfusion after the completion of contracture (after 20 min) had no effect on myocardial ATP-content. The results indicate that there is a transmural ATP gradient in ischaemic isolated rat heart and that myocardial ATP net production during reperfusion (10 min) is prevented after the development of ischaemic contracture.(ABSTRACT TRUNCATED AT 250 WORDS)