Moderation of postischemic damage to cardiomyocytic membranes with reperfusion solution

Isolated perfused hearts of Wistar rats subjected to total ischemia and reperfusion were used to examine the possibility of moderating damage to cardiomyocyte membranes with reperfusion solution containing l-aspartic acid, d-glucose, and d-mannitol. During the first 5 minutes of reperfusion, this solution significantly improved recovery of the pumping and contractile functions of the heart compared to the control and reduced the release of lactate dehydrogenase and systems generating short-living ROS into the effluent. To the end of reperfusion, the content of ATP and phosphocreatine was higher and the loss of total creatine was lower in hearts perfused with the test solution compared to the control. It is hypothesized that better integrity of the myocyte sarcolemma in hearts perfused with the test solution results from better preservation of macroergic phosphates and inhibition of ROS generation in this solution. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 1, pp. 20–22, January, 2007     

Propofol improves recovery of the isolated working hypertrophic heart from ischaemia–reperfusion

The general anaesthetic propofol shows promise in protecting normal hearts against various cardiac insults, but little is known about its cardioprotective potential in hypertrophic hearts. This study tested the hypothesis that propofol at a clinically relevant dose would enhance functional recovery in hypertrophic hearts following ischaemia. Hypertrophic hearts from spontaneously hypertensive rats and hearts from their normotensive controls, Wistar Kyoto Rats, were equilibrated in the working mode prior to global normothermic ischaemia. Reperfusion commenced with 10?min in Langendorff mode, followed by 30-min working reperfusion. Functional performance was measured throughout the working mode, whilst reperfusion damage was assessed from myocardial troponin I release during Langendorff reperfusion. Where used, 4?μg/ml propofol was added 10?min before ischaemia and was washed out 10?min into working reperfusion. An additional protocol investigated recovery of hearts protected by normothermic hyperkalaemic cardioplegic arrest. Following 20-min ischaemia, reperfusion damage was significantly worse in hypertrophic hearts compared to normal hearts, whilst addition of propofol to hypertrophic hearts significantly improved the aortic flow (31 ± 5.8 vs. 11.6 ± 2.0?ml/min, n?=?6–7 ± SE, p?<?0.05). Propofol also conferred significant protection following 30-min ischaemia where the recovery of cardiac output and stroke volume was similar to that for cardioplegia alone. Incubation with propofol improved the NADH/NAD⁺ ratio in freshly isolated cardiomyocytes from hypertrophic hearts, suggesting possible improvements in metabolic flux. These findings suggest that propofol at the clinically relevant dose of 4?μg/ml is as effective as cardioplegic arrest in protecting hypertrophic hearts against ischaemia–reperfusion.     

Role of cannabinoid receptors in the regulation of cardiac contractility during ischemia/reperfusion

We studied the effect of selective ligands of cannabinoid (CB) receptors on contractility of isolated Langendorff-perfused rat heart under conditions of 45-min total ischemia and 30-min reperfusion. Perfusion with a solution containing selective CB receptor agonist HU-210 for 10 min before ischemia increased the severity of reperfusion contractile dysfunction. This drug decreased left ventricular developed pressure and maximum rates of contraction and relaxation, but had no effect on heart rate and end-diastolic pressure. The negative inotropic effect of the drug was transitory and disappeared after 5-min reperfusion. Pretreatment with selective CB1 receptor antagonist SR141716A and selective CB2 receptor antagonist SR144528 had no effect on heart rate and myocardial contractility during reperfusion. Our results indicate that stimulation of CB receptors can increase the degree of reperfusion-induced cardiac contractile dysfunction. However, endogenous cannabinoids are not involved in the development of myocardial contractile dysfunction during ischemia/reperfusion of the isolated heart. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 11, pp. 500–504, November, 2006     

Different preservation of myocardial capillary endothelial cells and cardiomyocytes during and after cardioplegic ischemia (25 degrees C) of canine hearts

Complete resumption of cardiac function after cardioplegic arrest presupposes a well-preserved myocardial ultrastructure during and after ischemia. Therefore, we determined ischemia-induced ultrastructural alterations in the myocardium during and after reversible cardioplegic ischemia using stereological methods. Cardiac arrest was induced with St. Thomas' Hospital- or Custodiol (HTK) solution. Reperfusion with Tyrode's solution followed after reversible cardioplegic ischemia in situ. Samples were taken 1) from beating hearts, 2) from cardioplegically arrested hearts immediately after the end of coronary perfusion, 3) from ischemic hearts incubated in the cardioplegic solution at 25 degrees C, and 4) from reperfused beating hearts after ischemia in situ at 22 degrees C. Cellular swelling was determined as the barrier thickness of capillary endothelium and as the sum of cardiomyocyte volume fractions of free sarcoplasm and mitochondria. In St. Thomas'-arrested hearts, intraischemic volume increase was significantly more pronounced in endothelial cells than in cardiomyocytes. Reperfusion at the intraischemic practical limit of resuscitability (ATP levels of 4 micromol/gww) significantly reduced intraischemic swelling of cardiomyocytes, but not of capillary endothelial cells. Mitochondrial damage was more pronounced in capillary endothelial cells during ischemia and after reperfusion. Thus, after reversible cardioplegic arrest, structural recovery of cardiomyocytes is better than that of capillary endothelial cells. An incomplete structural protection of capillary endothelial cells may predominantly contribute to postischemic dysfunction in the reperfused heart.     

Metabolic correction reduces the area of acute ischemic myocardial infarction in rats

The possibility of decreasing the degree of irreversible alterations in cardiomyocytes with original saline reperfusion solution enriched with L-aspartic acid, D-glucose, and D-mannitol was studied on experimental rats with regional ischemia and reperfusion. Infusion of the test solution into the left ventricle during the early reperfusion stage significantly reduced the area of myocardial infraction. This effect was accompanied by improvement of energy metabolism and decrease in damage to cell membranes in the risk zone. Our results indicate that metabolic protection during reperfusion increases myocardial resistance to ischemic and reperfusion stress. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 3, pp. 267–269, March, 2006     

Polymorphonuclear granulocytes induce myocardial dysfunction during ischemia and in later reperfusion of hearts exposed to low-flow ischemia

Polymorphonuclear granulocytes (PMNs) are known to contribute to reperfusion injury of the heart. However, whether PMNs compromise myocardial function of hearts exposed to a low-flow ischemia has not been determined. Moreover, not much is known about deleterious effects of PMNs at different times during ischemia and reperfusion. Isolated, working guinea pig hearts were subjected to 30 min of low-flow ischemia and reperfusion. Homologous PMNs were applied as 1-min boluses in the presence of thrombin during either ischemia or the first or fifth minute of reperfusion, and postischemic recovery of external heart work (REHW) and intracoronary PMN retention (PMNR) were quantified. In further experiments, the radical scavenger superoxide dismutase (SOD) was added. Compared with controls without PMNs (REHW, 92.4%), application of PMNs led to a significant loss of myocardial function, which was detected at all three examination times. Moreover, intracoronary PMNR increased significantly in comparison with that of controls with hearts not exposed to ischemia or reperfusion. On the other hand, addition of SOD significantly increased REHW. Intracoronary PMNR was not significantly changed by coapplication of SOD. We conclude that thrombin-stimulated PMNs applied at different times during ischemia and reperfusion significantly impaired cardiac function in hearts exposed to a low-flow ischemia.     

Comparison of enoximone,amrinone, or levosimendan enriched St. Thomas' hospital cardioplegic solutions used for myocardial preservation in isolated guinea pig hearts

Myocardial contractile function after cardioplegic arrest is often depressed and an ideal cardioplegic solution has not been developed yet. The aim of this study was to assess the efficacy of phosphodiesterase III inhibitors, amrinone and enoximone, and levosimendan, a novel Ca2+ sensitizing agent, on recovery of hearts after normothermic cardioplegic arrest when added to the St. Thomas' hospital cardioplegic solution. In the control group, isolated guinea pig hearts were perfused in Langendorff apparatus and arrested with standard St. Thomas' solution. In other groups, amrinone (10(-5) mol.L-1), levosimendan (10(-5) mol.L-1), or enoximone (10(-4) mol.L-1) were added to the cardioplegic solution. In all hearts, intraventricular pressure, +dp/dtmax, -dp/dtmax, area under pressure-time curve, heart rate, coronary flow, lactate dehydrogenase and creatine kinase enzyme leakage, and oxygen consumption were measured. In the enoximone group, contractility force and +dp/dtmax, were found to be significantly high in the reperfusion and inotropic periods in comparison with other groups (p < 0.05). -dp/dtmax and area under contractility-time curve values were significantly high in inotropic period in enoximone group (p < 0.05). No statistically significant difference was noted in other groups. Cardioplegic solution enrichment with enoximone augmented mechanic functions in reperfusion period. No positive effect of amrinone or levosimendan was observed in this study.     

Cardioprotective effect of histidine-containing dipeptides in pharmacological cold cardioplegia

The cardioprotective effect of cardioplegic solution based on histidine-containing dipeptides was evaluated on isolated rat heart under conditions of hyporthermia and long ischemia. The use of natural dipeptides in cardioplegic solutions promoted an increase in the buffer capacity of myocardial cells and creation of an additional anti-ischemic effect under conditions of long ischemia and hypothermia. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 3, pp. 291–295, March, 2008     

Antiarrhythmic and arrhythmogenic effects of L-carnitine in ischemia and reperfusion

Isolated rat hearts were subjected to 30-min coronary artery occlusion followed by 120-min reperfusion. The hearts (n=8–12) were perfused with Krebs-Henseleit solution enriched with L-carnitine (0.5, 2.5 and 5 mM) for 10 min before and after ischemia or reperfusion and for the whole period of ischemia and reperfusion. Two-hour perfusion with L-carnitine during ischemia/reperfusion markedly (p<0.05) and dose-dependently decreased the incidence of ventricular tachycardia (VT, maximum 65%). The incidence of reperfusion ventricular fibrillation (VF) also decreased from 63% (control) to 17% in hearts perfused with 5 mM L-carnitine, as reflected by a significant (p<0.05) decline in VF duration from 218±99 sec in control to 19±19 sec. Perfusion of etomoxir (palmitoylcarnitinetransferase-1 inhibitor) along with L-carnitine reversed the antiarrhythmogenic action of L-carnitine. Interestingly, short time preischemic administration of L-carnitine produced a concentration-dependent arrhythmogenic effects on both ischemia and reperfusion-induced arrhythmias. These results show that L-carnitine produced a protective effect against reperfusion arrhythmias only when it was perfused for the whole period of the experiment. This protective action was reversed by concomitant use of etomoxir, suggesting that the efficacy of L-carnitine is due to its mitochondrial action but cannot be solely attributed to increased fatty acid oxidation. Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 146, No. 8, pp. 175–178, August, 2008     

Cardioprotective Effect of Ischemic Postconditioning on the Model of Isolated Heart

Irreversible cardiomyocyte damage was induced by 45-min global ischemia followed by 30-min reperfusion in Langendorff-perfused isolated rat heart. Cell damage was assessed by the release of creatine phosphokinase into the perfusate. The hearts were subjected to the following postconditioning protocols: 1) three cycles of 10-sec reperfusion and 10-sec ischemia, total cycle time 20 sec; 2) six cycles of 10-sec reperfusion and 10-sec ischemia, total cycle time 20 sec; 3) three sessions of 20-sec reperfusion and 20-sec ischemia, total cycle time 40 sec; 4) 6 cycles of 20-sec reperfusion and 20-sec ischemia, total cycle time 40 sec; 5) 3 cycles of 30-sec reperfusion and 30-sec ischemia, total cycle time 60 sec. It was found that only postconditioning with a total cycle time of 40 sec or 60 sec prevents myocardial reperfusion injury.     

二氮嗪后处理对离体大鼠心功能及线粒体心磷脂的影响

目的:建立离体大鼠心肌缺血/再灌注损伤模型,观察二氮嗪(diazoxide,D)后处理对缺血/再灌注损伤离体大鼠心功能及线粒体心磷脂的影响,并探讨ATP敏感性钾通道在二氮嗪后处理心肌保护中的作用。方法:采用Langendorff装置建立离体大鼠心肌缺血/再灌注损伤模型,将SD大鼠随机分为对照组(control)、缺血再灌注模型组(I/R)、二氮嗪后处理组(I/R+D)、5-羟葵酸拮抗二氮嗪后处理组(I/R+5-HD+D),每组8只,均先灌注平衡20 min。Control组:灌注平衡后续灌70 min;I/R组:缺血前灌注4℃ST.Thomas停跳液,全心缺血40 min,再灌30 min;I/R+D组:全心缺血40 min,缺血后给予含二氮嗪(50μmol/L)的K-H液灌注5 min后,再灌25 min;I/R+5-HD+D组:二氮嗪后处理前给予含5-羟葵酸(100μmol/L)的K-H液灌注5 min,再灌20 min。观察各组续(再)灌注末心率、冠脉流出液量、心功能、心肌酶学及心肌线粒体心磷脂的变化。结果:各组续(再)灌注末比较,I/R组较control组及I/R+D组心率减慢、冠脉流出液量降低,心功能明显受损,心肌酶增加,心磷酯含量减少,但与I/R+5-HD+D无明显差异。结论:二氮嗪后处理通过增加线粒体心磷脂含量,减少心肌酶的释放,改善心脏功能,减轻心肌的再灌注损伤,产生心肌保护作用。5-羟葵酸能够完全阻断二氮嗪的心肌保护作用。     

Involvement of Ca(2+) in antiarrhythmic effect of ischemic preconditioning in isolated rat heart

We investigated the relationship between the effects of ischemic preconditioning (IPC) and Ca(2+) preconditioning (CPC) on reperfusion-induced arrhythmias. In the control group (noPC), Langendorff-perfused rat hearts were subjected to 5-min zero-flow global ischemia (I) followed by 15-min reperfusion (I/R). In ischemic preconditioning groups (IPC), the hearts were subjected to three cycles of 3-min global ischemia and 5-min reperfusion. In the CPC group, the hearts were exposed to three cycles of 3-min perfusion of higher Ca(2+) (2.3 mmol/l Ca(2+)) followed by 5-min perfusion of normal 1.3 mmol/l Ca(2+), and the hearts were then subjected to I/R. Verapamil was administered in several hearts of the IPC group (VR+IPC). Ventricular arrhythmias upon reperfusion were less frequently seen in the IPC and CPC groups than in the noPC and VR+IPC groups. IPC and CPC could attenuate conduction delay and enhance shortening of the monophasic action potential duration during ischemia. The ventricular fibrillation threshold measured at 1-min reperfusion was significantly higher in the IPC and CPC groups than in the noPC and VR+IPC groups. Verapamil completely abolished the salutary effects of IPC. These results demonstrate that Ca(2+) plays an important role in the antiarrhythmic effect of IPC during reperfusion.     

Activation of μ-opiate receptors as a factor of regulation of heart resistance to ischemia-reperfusion and oxidative stress

Intravenous injection of the selective μ-opiate receptor agonist DAMGO (0.1 mg/kg, 15 min before isolation of the heart) improved resistance of isolated perfused rat heart to ischemia (45 min) and reperfusion (60 min) damages.In vivo administration of DAMGO prevented reperfusion-induced damages to cardiomyocytes and decreased the content of conjugated dienes in the myocardium during ischemia-reperfusionin vitro. Furthermore, stimulation of μ-opiate receptors promoted recovery of myocardial contractility during reoxygenation, but had no effect on heart resistance to free radical-induced damages during perfusion of isolated heart with a solution containing Fe²⁺ and ascorbic acid. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 8, pp. 163–167, August, 2000     

尼可地尔激活RISK通路减轻高胆固醇大鼠心肌缺血/再灌注损伤

目的探讨尼可地尔对高胆固醇大鼠心肌缺血/再灌注损伤的影响及其可能机制。方法应用高胆固醇饮食喂养健康雄性Wistar大鼠8周建立高胆固醇大鼠模型,应用Langendorff灌流装置采用全心缺血30min和再灌注120min建立离体心脏缺血/再灌注(I/R)模型。在缺血前或再灌注即刻灌注含有尼可地尔的KH液10min以制备尼可地尔药物预处理(NIC-pre)与后处理(NIC-post)模型。通过TTC染色测量心肌梗死面积、TUNEL染色检测心肌细胞凋亡率,Western blot检测RISK通路p-Akt和p-Erk1/2蛋白表达水平。结果与I/R对照组相比,NIC-30pre组与NIC-30post组均可降低心肌梗死面积和心肌细胞凋亡率,并显著上调p-Akt和pErk1/2的表达水平。结论尼可地尔减轻高胆固醇大鼠心肌缺血/再灌注损伤,与其激活RISK通路相关。     

Antiarrhythmic effect of heat adaptation in ischemic and reperfusion injury to the heart

Study on a model of 6-day dosed adaptation to heat in rats showed that this adaptation decreased the severity of cardiac arrhythmias during ischemic and reperfusion injury. The duration of arrhythmias decreased not only in the ischemic period, but also under conditions of reperfusion. Adaptation delayed the development of arrhythmias during ischemia, decreased the number of animals with late reperfusion arrhythmias, and improved recovery of the heart after ischemia and reperfusion. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 1, pp. 13–16, January, 2007     

Mechanical unloading and infarct size: studies with the heterotopically transplanted rabbit heart.

The possibility that unloading the heart during regional ischemia and/or reperfusion may limit infarct size was investigated by inducing regional ischemia in both a heterotopically transplanted heart (unloaded) and the recipient's heart (loaded control). In this way, the extent of myocardial infarction was compared in paired hearts in the same animal under similar experimental conditions. Hearts excised from donor rabbits, were arrested with St. Thomas' Hospital cardioplegic solution and maintained at 15 degrees C for 1 hour during which time they were transplanted into the necks of recipient rabbits. 24 hours later, rabbits were reanesthetized and the left circumflex coronary artery ligated in both the transplanted and the recipient's hearts. After 1 hour of regional ischemia hearts were reperfused for 3 hours. The transplanted heart was paced at 205 beats per minute (bpm) throughout the experiment. Similar values for infarct size were obtained in both the loaded and unloaded hearts (73 +/- 4% vs 75 +/- 6%, respectively). No significant differences were seen in any other parameters. In conclusion, our results suggest that during regional ischemia the amount of work performed by the heart does not appear to be a major factor in determining the ultimate size of an infarct.     

Attenuation of conduction delay by ischemic preconditioning reduces ischemia-induced ventricular arrhythmias

Ischemic preconditioning has been acknowledged as a powerful method of decreasing ischemic injury. However, the antiarrhythmic mechanism of ischemic preconditioning during ischemia is unclear. We studied the effects of ischemic preconditioning on arrhythmias and cardiac electrophysiology during ischemia in Langendorff rat hearts (n = 44). In the non-preconditioned group (PC(-); n = 24), the hearts underwent 5-min zero-flow global ischemia without any prior ischemic preconditioning. In the preconditioned group (PC(+); n = 20), the hearts were preconditioned by three cycles of 3-min zero-flow global ischemia and 5-min reperfusion before undergoing 5-min global ischemia. Ischemic preconditioning reduced the incidence of ischemia-induced arrhythmias (PC(-); 38.9%, PC(+): 8.3%, p < 0.05), shortened monophasic action potential duration (MAPD, P < 0.05), attenuated conduction delay (conduction time; PC(-): 234.2%, PC(+): 173.4%, P < 0.05) and increased the ventricular fibrillation threshold. Although the shortening of MAPD in PC(-) hearts was not influenced by the presence or absence of arrhythmias, conduction time prolongation at 3-min was more obvious in PC(-) hearts with arrhythmia than in PC(-) hearts without arrhythmia (PC(-) with arrhythmia: 220.2%, PC(-) without arrhythmia: 190.7%, P < 0.05). We concluded that ischemic preconditioning could protect the rat hearts from ischemia-induced arrhythmias and postulated that attenuation of conduction delay during ischemia might be an important factor in the antiarrhythmic action of ischemic preconditioning.     

The role of the L-arginine/nitric oxide pathway in myocardial ischaemic and reperfusion injury

Myocardial ischaemia followed by reperfusion (I/R) is associated with impaired endothelial function including diminished release and/or effects of nitric oxide (NO) which may contribute to the development of I/R injury. The aim of the present study was to investigate the role of the L-arginine/NO pathway in myocardial I/R injury. In isolated rat hearts subjected to global ischaemia followed by reperfusion L-arginine and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), but not D-arginine, significantly enhanced the recoveries of mycardial performance and coronary flow, and reduced the area of no-reflow and creatine kinase outflow. The NO synthase inhibitor NG-nitro-L-arginine (L-NNA) abolished the protective effects of L-arginine. Endothelium-dependent vasodilatation after I/R was preserved in L-arginine treated but not in vehicle hearts. Following I/R Ca2+-dependent NO synthase activity was reduced by 90% in comparison with non-ischaemic hearts. L-arginine but not D-arginine significantly increased NO synthase activity. In anaesthetized pigs, L-arginine given by local coronary venous retroinfusion reduced myocardial infarct size induced by 45 min of coronary artery ligation and 4 h of reperfusion to 35% of the area at risk from 76% in controls. The protective effect of L-arginine was blocked by L-NNA. Acetylcholine-induced coronary vasodilatation following I/R was attenuated in controls but not in L-arginine treated pigs. It is concluded that L-arginine or the NO donor SNAP reduces I/R-induced myocardial and endothelial injury. The protective effect of L-arginine seems to be mediated through maintained production of NO by preserving the function of Ca2+-dependent NO synthase in the heart.     

Protective effects of N-(2-mercaptopropionyl)-glycine against ischemia–reperfusion injury in hypertrophied hearts

The beneficial effects of N-(2-mercaptopropionyl)-glycine (MPG) against ischemia–reperfusion injury in normotensive animals have been previously studied. Our objective was to test the action of MPG during ischemia and reperfusion in hearts from spontaneously hypertensive rats (SHR). Isolated hearts from SHR and age-matched normotensive rats Wistar Kyoto (WKY) were subjected to 50-min global ischemia (GI) and 2-hour reperfusion (R). In other hearts MPG 2 mM was administered during 10 min before GI and the first 10 min of R. Infarct size (IS) was assessed by TTC staining technique and expressed as percentage of risk area. Postischemic recovery of myocardial function was assessed. Reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS) and SOD cytosolic activity — as estimators of oxidative stress and MnSOD cytosolic activity — as an index of (mPTP) opening were determined. In isolated mitochondria H₂O₂-induced mPTP opening was also measured. The treatment with MPG decreased infarct size, preserved GSH levels and decreased SOD and MnSOD cytosolic activities, TBARS concentration, and H₂O₂ induced-mPTP opening in both rat strains. Our results show that in both hypertrophied and normal hearts an attenuation of mPTP opening via reduction of oxidative stress appears to be the predominant mechanism involved in the cardioprotection against reperfusion injury MPG-mediated.     

Role of adenosine receptor activation in antioxidant enzyme regulation during ischemia-reperfusion in the isolated rat heart

The aim of the present study was to investigate the protective role of pharmacological preconditioning on antioxidant enzymes using A(1) and A(3) adenosine receptor agonists in the recovery of the isolated myocardium after cardioplegic ischemia. Two different modes of preconditioning were studied: isolated rat hearts were perfused with A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA) or A(3) 2-chloro-N(6)-(3-iodobenzyl) adenosine-5'-N-methyluronamide (Cl-IB-MECA) (1 nM), followed by cardioplegic ischemia and reperfusion (30 min each) (perfusion mode), or CCPA or Cl-IB-MECA (100 micro g/kg) were injected intravenously 24 h before the experiment (injection mode). Hearts treated with CCPA improved in terms of mechanical function, infarct size, ATP levels, superoxide dismutase, and catalase (p < 0.005) in both modes of administration. Cl-IB-MECA was beneficial mainly in the injected group. Reduced damage to the mitochondria in the CCPA-treated hearts was observed using electron microscopy evaluation. In the Cl-IB-MECA-injected hearts, mitochondrial damage was moderate. CCPA in both modes of treatment and Cl-IB-MECA in the injected mode were beneficial in protecting the perfused isolated rat heart, subjected to normothermic cardioplegic ischemia. This protection was partially related to the higher myocardial activity of superoxide dismutase and catalase.