Effect of acute and chronic simvastatin treatment on post-ischemic contractile dysfunction in isolated rat heart

Statins are powerful lipid-lowering drugs, widely used in patients with hyperlipidemia and coronary artery disease. It was found, however, that statins appear to have a pleiotropic effect beyond their lipid-lowering ability. They exert anti-inflammatory, antithrombotic and antioxidant effects, increase nitric oxide production and improve endothelial dysfunction. The aim of our study was to examine the effect of chronic and acute treatment with simvastatin on the contractile function of the isolated perfused rat heart after ischemia/reperfusion injury. Contractile function was measured on isolated rat hearts, perfused according to Langendorff under constant pressure. The hearts were subjected to 20 min of global ischemia, followed by 40 min of reperfusion. To investigate the acute effect, simvastatin at a concentration of 10 micromol/l was added to the perfusion solution during reperfusion. In chronic experiments the rats were fed simvastatin at a concentration of 10 mg/kg for two weeks before the measurement of the contractile function. Acute simvastatin administration significantly increased reparation of the peak of pressure development [(+dP/dt)(max)] (52.9+/-8.2 %) after global ischemia, as compared with the control group (28.8+/-5.2 %). Similar differences were also observed in the time course of the recovery of [(+dP/dt)(max)]. Chronic simvastatin was without any protective effect. Our results reveal that the acute administration of simvastatin during reperfusion, unlike the chronic treatment, significantly reduced contractile dysfunction induced by ischemia/reperfusion injury. This supports the idea of possible cardioprotective effect of statin administration in the first-line therapy of the acute coronary syndrome.     

Nitric oxide mediates protein kinase C isoform translocation in rat heart during postischemic reperfusion

It is controversial whether nitric oxide (NO) is protective or deleterious against ischemia-reperfusion injury. We examined the effect of NO on PKC isoform translocation and protection against ischemia-reperfusion injury in perfused heart. An NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester, 3.0 microM), administered only during reperfusion but not during ischemia, inhibited the translocation of PKC-alpha, -delta and -epsilon isoforms to the nucleus-myofibril fraction and the translocation of PKC-alpha to the membrane fraction after ischemia (20 min) and reperfusion (10 min) in the perfused rat heart. NO donors, 3-morpholinosydnonimine (SIN-1) or S-nitroso-N-acetylpenicillamine (SNAP) activated purified PKC in vitro. SIN-1 also induced PKC isoform translocation in perfused heart. On the other hand, PKC selective inhibitor, calphostin C (0.2 microM) or chelerythrine (1.0 microM), aggravated the contractile dysfunction of ischemic heart during reperfusion, when they were perfused during reperfusion. These data suggest that NO generated during reperfusion following ischemia activates PKC isoforms and may protect the heart against contractile dysfunction in the perfused rat heart.     

Effects of SM-20550, a selective Na+-H+ exchange inhibitor,on the ion transport of myocardial mitochondria

The study investigated the influence of L-carnitine on the formation of malondialdehyde, an indicator of lipid peroxidation, in isolated Langendorff rat hearts. Earlier investigations of hemodynamic parameters and the recovery of ATP and creatine phosphate, carried out by means of ³¹P-NMR spectroscopy, had demonstrated that, depending on the composition of the perfusates (content of glucose, fatty acids, and carnitine), quite strong differences may occur in the reperfusion period after ischemia.In order to determine a possible relationship between these differences and the addition of carnitine, the study investigated whether carnitine penetrated into the tissue during the experiments, and whether it was able to reduce the concentration of detrimental substances. The concentrations of free and total carnitine as well as the malondialdehyde content as an indicator of ischemia/reperfusion damage were determined in different parts of the cardiac tissue as follows: After the Langendorff-experiments the hearts were dissected, homogenized and reconditioned; then carnitine and malondialdehyde were determined. The study included 63 hearts, which were divided into 8 different perfusion groups.Carnitine concentrations in heart tissue perfused with L-carnitine were much higher than those of the controls. Since exogenous L-carnitine and formed esters could be found in the tissue after the experiment, they must have permeated the cellular membrane rapidly. The concentrations of malondialdehyde behaved in an inverted way; as expected they were lower in carnitine-perfused hearts. The favourable effects of L-carnitine, expressed both by improved cardiac dynamics and ATP and CrP recovery in the reperfusion period, are obviously due to the fact that L-carnitine reduces ischemic damage.     

Ischemic preconditioning in rat heart: No correlation between glycogen content and return of function

We tested the hypothesis that glycogen levels at the beginning of ischemia affect lactate production during ischemia and postischemic contractile function.Isolated working rat hearts were perfused at physiological workload with bicarbonate buffer containing glucose (10 mmol/L). Hearts were subjected to four different preconditioning protocols, and cardiac function was assessed on reperfusion. Ischemic preconditioning was induced by either one cycle of 5 min ischemia followed by 5, 10, or 20 min of reperfusion (PC5/5, PC5/10, PC5/20), or three cycles of 5 min ischemia followed by 5 min of reperfusion (PC3 × 5/5). All hearts were subjected to 15 min total, global ischemia, followed by 30 min of reperfusion. We measured lactate release, timed the return of aortic flow, compared postischemic to preischemic power, and determined tissue metabolites at selected time points.Compared with preischemic function, cardiac power during reperfusion improved in groups PC5/10 and PC5/20, but was not different from control in groups PC5/5 and PC3 × 5/5. There was no correlation between preischemic glycogen levels and recovery of function during reperfusion. There was also no correlation between glycogen breakdown (or resynthesis) and recovery of function. Lactate accumulation during ischemia was lowest in group PC5/20 and highest in the group with three cycles of preconditioning (PC3 × 5/5). Lactate release during reperfusion was significantly higher in the groups with low recovery of power than in the groups with high recovery of power.In glucose-perfused rat heart recovery of function is independent from both pre- and postischemic myocardial glycogen content over a wide range of glycogen levels. The ability to utilize lactate during reperfusion is an indicator for postischemic return of contractile function.     

Effects of natural antioxidant Ginkgo biloba extract (EGB 761) on myocardial ischemia-reperfusion injury

Recently, it was reported that Ginkgo biloba extract (EGb 761), which is known to have antioxidant properties, also has antiarrhythmic effects on cardiac reperfusion-induced arrhythmias. In the present study, effects of EGb 761 on cardiac ischemia-reperfusion injury were investigated from the point of view of recovery of mechanical function as well as the endogenous antioxidant status of ascorbate. Isolated rat hearts were perfused using the Langendorff technique, and 40 min of global ischemia were followed by 20 min of reperfusion. EGb 761 improved cardiac mechanical recovery and suppressed the leakage of lactate dehydrogenase (LDH) during reperfusion. Furthermore, EGb 761 diminished the decrease of myocardial ascorbate content after 40 min of ischemia and 20 min of reperfusion. Interestingly, EGb 761 also suppressed the increase of dehydroascorbate. These results indicate that EGb 761 protects against cardiac ischemia-reperfusion injury and suggest that the protective effects of EGb 761 depend on its antioxidant properties.     

Influence of fasting on the effects of ischemic preconditioning in the ischemic-reperfused rat heart

The effects of fasting and ischemic preconditioning (IP) on heart function of Langendorff-perfused rat hearts exposed to 25 min global ischemia plus 30 min reperfusion (RP), were correlated with lactate release and tissue-levels of long-chain acyl carnitine (LCCa) and CoA (LCCoA). IP was achieved by a 3 min ischemia plus a 5 min reperfusion cycle. Creatine kinase leakage was measured to assess the extent of cardiac injury. Fasting reduced the ischemic-induced contracture, improved RP recovery of mechanical function, reduced lactate release and increased the end-ischemia LCCoA and LCCa levels. Both in the fed and the fasted rat hearts IP delayed the pacemaker depression, reduced the amplitude of ischemic contracture and improved the RP recovery of contraction. However, IP reduced creatine kinase and lactate release only in the fed rat hearts. IP had no effects on tissue LCCa and LCCoA in both groups. These data suggest that: 1) beneficial effects of fasting may be ascribed, at least in part, to a reduced lactate production which may attenuate ischemic myocyte acidification and to the accumulation of fatty acyl esters which would favour citric acid cycle replenishment during RP. 2) beneficial effects of IP could be in part explained by the reduction of lactate production in the fed group although data obtained with the fasted rat heart indicate that another mechanisms must also be involved in the effects of IP. 3) accumulation of LCCoA and LCCa is not involved in the noxious effects of ischemia as well as in the protection effected by IP.     

Ischemic preconditioning-mediated restoration of membrane dystrophin during reperfusion correlates with protection against contraction-induced myocardial injury

Dystrophin is an integral membrane protein involved in the stabilization of the sarcolemmal membrane in cardiac muscle. We hypothesized that the loss of membrane dystrophin during ischemia and reperfusion is responsible for contractile force-induced myocardial injury and that cardioprotection afforded by ischemic preconditioning (IPC) is related to the preservation of membrane dystrophin. Isolated and perfused rat hearts were subjected to 30 min of global ischemia, followed by reperfusion with or without the contractile blocker 2,3-butanedione monoxime (BDM). IPC was introduced by three cycles of 5-min ischemia and 5-min reperfusion before the global ischemia. Dystrophin was distributed exclusively in the membrane of myocytes in the normally perfused heart but was redistributed to the myofibril fraction after 30 min of ischemia and was lost from both of these compartments during reperfusion in the presence or absence of BDM. The loss of dystrophin preceded uptake of the membrane-impermeable Evans blue dye by myocytes that occurred after the withdrawal of BDM and was associated with creatine kinase release and the development of contracture. Although IPC did not alter the redistribution of membrane dystrophin induced by 30 min of ischemia, it facilitated the restoration of membrane dystrophin during reperfusion. Also, myocyte necrosis was not observed when BDM was withdrawn after complete restoration of membrane dystrophin. These results demonstrate that IPC-mediated restoration of membrane dystrophin during reperfusion correlates with protection against contractile force-induced myocardial injury and suggest that the cardioprotection conferred by IPC can be enhanced by the temporary blockade of contractile activity until restoration of membrane dystrophin during reperfusion.     

Myocardial contractile function during postischemic low-flow reperfusion: critical thresholds of NADH and O2 delivery

The degree of myocardial oxygen delivery (Do2) that is necessary to reestablish functional contractile activity after short-term global ischemia in heart is not known. To determine the relationship between Do2 and recovery of contractile and metabolic functions, we used tissue NADH fluorometric changes to characterize adequacy of reperfusion flow. Isolated perfused rat hearts were subjected to global ischemia and were reperfused at variable flow rates that ranged from 1 to 100% of baseline flow. Myocardial function and tissue NADH changes were continuously measured. NADH fluorescence rapidly increased and plateaued during ischemia. A strong inverse logarithmic correlation between NADH fluorescence and reperfusion Do2 was demonstrated (r = -0.952). Left ventricular function (rate-pressure product) was inversely related to NADH fluorescence at reperfusion flows from 25 to 100% of baseline (r = -0.922) but not at lower reperfusion flow levels. An apparent reperfusion threshold of 25% of baseline Do2 was necessary to resume contractile function. At very low reperfusion flows (1% of baseline), another threshold flow was identified at which NADH levels increased beyond that observed during global ischemia (3.4 +/- 3.0%, means +/- SE, n = 9), which suggests further reduction of the cellular redox state. This NADH increase at 1% of baseline reperfusion flow was blocked by removing glucose from the perfusate. NADH fluorescence is a sensitive indicator of myocardial cellular oxygen utilization over a wide range of reperfusion Do2 values. Although oxygen is utilized at very low flow rates, as indicated by changes in NADH, a critical threshold of approximately 25% of baseline Do2 is necessary to restore contractile function after short-term global ischemia.     

Effects of L-carnitine on mechanical recovery of isolated rat hearts in relation to the perfusion with glucose and palmitate

The purpose of this study was to investigate the effects of L-carnitine on the hemodynamic parameters of Langendorff hearts. Isolated rat hearts were perfused with various solutions containing high or low concentrations of fatty acids, additional glucose or no glucose, and L-carnitine or no L-carnitine. The most interesting part of the experiments was the behaviour of the hearts in the reperfusion period after no-flow ischemia of 20 min. The results were: (1) With glucose and high fatty acid concentrations the hearts showed an improved recovery of the left ventricular functions in the reperfusion period compared with low fatty acid concentrations. Without glucose the left ventricular pressure is much lower in the reperfusion period. (2) Addition of L-carnitine improved the recovery of the ischemically damaged hearts. This improvement is especially impressive at low fatty acid concentrations. L-carnitine addition at high fatty acid concentrations but without glucose strongly improved reperfusion behaviour. (3) The coronary flow is increased by 2 experimental conditions: (i) perfusion at low levels of fatty acids, carnitine and with glucose and (ii) high levels of fatty acids and carnitine but without glucose. These findings suggest that supplementation of L-carnitine has a beneficial effect on the isolated heart under various conditions, and possibly on specific human heart diseases.     

Effects of 5-hydroxydecanoate and ischemic preconditioning on the ischemic-reperfused heart of fed and fasted rats

This investigation aimed to assess whether the mitochondrial ATP-sensitive potassium channel blocker 5-hydroxydecanoate (5-HD) could abolish the protection conferred by fasting and ischemic preconditioning (IPC) and to ascertain whether these effects are associated with glycogen breakdown and glycolytic activity. Langendorff perfused hearts of fed and 24-h fasted rats were exposed to 25 min ischemia plus 30 min reperfusion. IPC was achieved by a 3 min ischemia plus a 5 min reperfusion cycle. 5-HD (100 microM) perfusion begun 5 min before IPC or 13 min before sustained ischemia in the non preconditioned groups. Fasting improved the reperfusion recovery of contraction, decreased the contracture and the lactate production, increased glycogenolysis and did not affect the percentage of viable tissue. 5-HD abolished the effects of fasting on the contractile recovery but did not affect the contracture. 5-HD decreased the lactate production in the fed group, increased the preischemic glycogen content in both nutritional groups and did not affect the ischemic glycogen fall. IPC improved the contractile function but prevented the contracture only in the fed group, reduced lactate accumulation and glycogenolysis and evoked an increase of the viable tissue. 5-HD abolished the effects of IPC on the contractile recovery and did not affect its effect on the contracture, lactate production, glycogenolysis and viable tissue. These data suggest that the mitocondrial ATP-sensitive potassium channel is involved in the effects of fasting and IPC on the contractile function but the other cardioprotective and metabolic effects appear evoked through other mechanisms. Also suggest that besides the inhibition of the mitochondrial potassium channel, other mechanisms mediate the effects of 5-HD.     

Effects of L-carnitine and its derivatives on postischemic cardiac function,ventricular fibrillation and necrotic and apoptotic cardiomyocyte death in isolated rat hearts

The study aimed to examine whether L-carnitine and its derivatives, acetyl-L-carnitine and propionyl-L-carnitine, were equally effective and able to improve postischemic cardiac function, reduce the incidence of reperfusion-induced ventricular fibrillation, infarct size, and apoptotic cell death in ischemic/reperfused isolated rat hearts. There are several studies indicating that L-carnitine, a naturally occurring amino acid and an essential cofactor, can improve mechanical function and substrate metabolism not only in hypertrophied or failing myocardium but also in ischemic/reperfused hearts. The effects of L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine, on the recovery of heart function, incidence of reperfusion-induced ventricular fibrillation (VF), infarct size, and apoptotic cell death after 30 min ischemia followed by 120 min reperfusion were studied in isolated working rat hearts. Hearts were perfused with various concentrations of L-carnitine (0.5 and 5 mM), acetyl-L-carnitine (0.5 and 5 mM), and propionyl-L-carnitine (0.05, 0.5, and 5 mM), respectively, for 10 min before the induction of ischemia. Postischemic recovery of CF, AF, and LVDP was significantly improved in all groups perfused with 5 mM of L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. Significant postischemic ventricular recovery was noticed in the hearts perfused with 0.5 mM of propionyl-L-carnitine, but not with the same concentration of L-carnitine or L-acetyl carnitine. The incidence of reperfusion VF was reduced from its control value of 90 to 10% (p < 0.05) in hearts perfused with 5 mM of propionyl-L-carnitine only. Other doses of various carnitines failed to reduce the incidence of VF. The protection in CF, AF, LVDP, and VF reflected in a reduction in infarct size and apoptotic cell death in hearts treated with various concentrations of carnitine derivatives. The difference between effectiveness of various carnitines on the recovery of postischemic myocardium may be explained by different membrane permeability properties of carnitine and its derivatives.     

间歇性低压低氧方式对发育大鼠心脏缺血/再灌注损伤的影响

本研究旨在探讨两种不同形式的间歇性低压低氧（intermittent hypobaric hypoxia,IHH）对发育大鼠心脏缺血,再灌注损伤的影响。雄性Sprague-Dawley（SD）新生大鼠72只,随机分为三组：对照组、IHH3000in组（IHH3000）、IHH5000m组（IHH5000）。低氧组大鼠出生后立即于低压氧舱分别接受28d、42d和56d（海拔5000m、每天6h：海拔3000m、每天5h）的低压低氧处理。应用Langendorff离体心脏灌流技术,给予心脏缺血（停灌30min）／再灌注（复灌60min）处理,分别在缺血前5min及复灌后l、5、10、20、30、60min记录心功能和冠状动脉流量变化,并测定乳酸脱氢酶（1actate dehydrogenase,LDH）活性。实验结束时测定心脏重量。结果显示：（1）IHH3000组大鼠体重增长与对照组无明显差异;IHH5000组大鼠体重增长明显慢于对照组及IHH3000组大鼠（P〈0．01）。（2）IHH3000组人鼠表现明显的心脏保护效应。与对照组相比较,在心脏停灌,再灌注60min时,心功能（LVDP、±LVdp／drmax）恢复增强（P〈0．05）、LDH活性降低（P〈0．05）、冠状动脉流量增多（P〈0．05）;心脏重量与对照组大鼠无差异;IHH42d处理的大鼠心功能恢复明显好于IHH28d处理的大鼠（P〈0．05）。（3）IHH5000组大鼠表现出明显的心脏损伤效应,各项心功能指标（LVDP、±LVdp／dtmax）的恢复均低于对照组（P〈0．05）,复灌过程中LDH活性明显高于相应对照组（P〈0．05）,右心室重量明显高于对照组大鼠（P〈0．05）。结果表明,适当的IHH增强发育大鼠心脏对缺血,再灌注损伤的抵抗能力;间歇性低氧方式是影响其心脏保护作用的重要因素。     

Differential effects of heptanoate and hexanoate on myocardial citric acid cycle intermediates following ischemia-reperfusion.

In the normal heart, there is loss of citric acid cycle (CAC) intermediates that is matched by the entry of intermediates from outside the cycle, a process termed anaplerosis. Previous in vitro studies suggest that supplementation with anaplerotic substrates improves cardiac function during myocardial ischemia and/or reperfusion. The present investigation assessed whether treatment with the anaplerotic medium-chain fatty acid heptanoate improves contractile function during ischemia and reperfusion. The left anterior descending coronary artery of anesthetized pigs was subjected to 60 min of 60% flow reduction and 30 min of reperfusion. Three treatment groups were studied: saline control, heptanoate (0.4 mM), or hexanoate as a negative control (0.4 mM). Treatment was initiated after 30 min of ischemia and continued through reperfusion. Myocardial CAC intermediate content was not affected by ischemia-reperfusion; however, treatment with heptanoate resulted in a more than twofold increase in fumarate and malate, with no change in citrate and succinate, while treatment with hexanoate did not increase fumarate or malate but increased succinate by 1.8-fold. There were no differences among groups in lactate exchange, glucose oxidation, oxygen consumption, and contractile power. In conclusion, despite a significant increase in the content of carbon-4 CAC intermediates, treatment with heptanoate did not result in improved mechanical function of the heart in this model of reversible ischemia-reperfusion. This suggests that reduced anaplerosis and CAC dysfunction do not play a major role in contractile and metabolic derangements observed with a 60% decrease in coronary flow followed by reperfusion.     

Protection of the reperfused heart by L-propionylcarnitine.

The effects of L-propionylcarnitine on mechanical function, creatine phosphate and ATP content, and lactate dehydrogenase leakage were studied in isolated perfused rat hearts exposed to global no-flow ischemia for 30 min followed by reperfusion for 20 min. Five and 10 mM L-propionylcarnitine resulted in a 100% recovery of left ventricular-developed pressure, whereas the recovery was only 40% in the hearts perfused without this agent. Ischemia-reperfusion caused a 85% loss of creatine phosphate and a 77% loss of ATP, which was prevented by 10 mM L-propionylcarnitine. Five millimolar L-propionylcarnitine protected the heart from the loss of creatine phosphate but not from the loss of ATP. Ten millimolar L-propionylcarnitine failed to improve the postischemic left ventricular-developed pressure, when it was added to the perfusate only after ischemia. L-propionylcarnitine alleviated the decrease of coronary flow in the reperfused hearts. Lactate dehydrogenase leakage was aggravated in the beginning of the reperfusion period by 10 mM L-propionylcarnitine. This adverse effect was, however, transient. L-Propionylcarnitine provides protection for the postischemic reperfused heart in a dose-dependent manner. The optimal time for administration is before the ischemic insult. High doses of this compound may perturb cell membrane integrity. Moreover, the present data point to an intracellular, metabolic, and perhaps anaplerotic mechanism of action of L-propionylcarnitine in cardiac ischemia-reperfusion injury.     

The nucleotide metabolism in lactate perfused hearts under ischaemic and reperfused conditions

It was examined whether lactate influences postischaemic hemodynamic recovery as a function of the duration of ischaemia and whether changes in high-energy phosphate metabolism under ischaemic and reperfused conditions could be held responsible for impairment of cardiac function. To this end, isolated working rat hearts were perfused with either glucose (11 mM), glucose (11 mM) plus lactate (5 mM) or glucose (11 mM) plus pyruvate (5 mM). The extent of ischaemic injury was varied by changing the intervals of ischaemia, i.e. 15, 30 and 45 min. Perfusion by lactate evoked marked depression of functional recovery after 30 min of ischaemia. Perfusion by pyruvate resulted in marked decline of cardiac function after 45 min of ischaemia, while in glucose perfused hearts hemodynamic performance was still recovered to some extent after 45 min of ischaemia. Hence, lactate accelerates postischaemic hemodynamic impairment compared to glucose and pyruvate. The marked decline in functional recovery of the lactate perfused hearts cannot be ascribed to the extent of degradation of high-energy phosphates during ischaemia as compared to glucose and pyruvate perfused hearts. Glycolytic ATP formation (evaluated by the rate of lactate production) can neither be responsible for loss of cardiac function in the lactate perfused hearts. Moreover, failure of reenergization during reperfusion, the amount of nucleosides and oxypurines lost or the level of high-energy phosphates at the end of reperfusion cannot explain lactate-induced impairment. Alternatively, the accumulation of endogenous lactate may have contributed to ischaemic damage in the lactate perfused hearts after 30 min of ischaemia as it was higher in the lactate than in the glucose or pyruvate perfused hearts. It cannot be excluded that possible beneficial effects of the elevated glycolytic ATP formation during 15 to 30 min of ischaemia in the lactate perfused hearts are counterbalanced by the detrimental effects of lactate accumulation.     

Mechanisms of attenuation of ischemic heart injury by means of a modified reperfusion

Mechanisms of attenuation of membrane injury and metabolic impairments in postischemic cardiomyocytes have been studied on a model of ischemic and reperfusion stress of rat heart using a modified early reperfusion. Optimization of the reperfusion infusate composition augmented recovery of cardiac pump and contractile function. This was accompanied by reduced release of lactate dehydrogenase activity and systems generating short-living reactive oxygen species into myocardial effluent and was associated with more efficient oxidative metabolism recovery and decreased losses of intracellular total creatine and amino acids pools. The results indicate perspectives of postischemic functional and metabolic myocardial injury correction by means of the controlled reperfusion.     

Urotensin II protects ischemic reperfusion injury of hearts through ROS and antioxidant pathway

Urotensin II (UII) is a vasoactive peptide which is bound to a G protein-coupled receptor. UII and its receptor are upregulated in ischemic and chronic hypoxic myocardium, but the effect of UII on ischemic reperfusion (I/R) injury is still controversial. The aim of the present study was to investigate whether UII protects heart function against I/R injury. Global ischemia was performed using isolated perfused Langendorff hearts of Sprague-Dawley rats. Hearts were perfused with Krebs-Henseleit buffer for 20min pre-ischemic period followed by a 20min global ischemia and 50min reperfusion. Pretreatment with UII (10nM) for 10min increased recovery percentage of the post-ischemic left ventricular developed pressure and ±dp/dt, and decreased post-ischemic left ventricular end-diastolic pressure as compared with I/R group. UII decreased infarct size and an increased lactate dehydrogenase level during reperfusion. Cardioprotective effects of UII were attenuated by pretreatment with UII receptor antagonist. The hydrogen peroxide activity was increased in UII-treated heart before ischemia. The Mn-SOD, catalase, heme oxygenase-1 and Bcl-2 levels were increased, and the Bax and caspase-9 levels were decreased in UII-treated hearts. These results suggest that UII has cardioprotective effects against I/R injury partly through activating antioxidant enzymes and reactive oxygen species.     

Evaluation of the role of xanthine oxidase in myocardial reperfusion injury

The free radical-generating enzyme xanthine oxidase has been hypothesized to be a central mechanism of the injury which occurs in postischemic tissues; however, its importance remains controversial. Much attention has focused on the role of this enzyme in myocardial reperfusion injury. While xanthine oxidase has been observed in ischemic tissue homogenates, the presence and importance of radical generation by the enzyme in intact tissues are unknown. Therefore, we performed electron paramagnetic resonance, nuclear magnetic resonance and hemodynamic studies to measure the presence and significance of xanthine oxidase-mediated free radical generation in the isolated rat heart. When isolated perfused rat hearts were reperfused after 30 min of global ischemia, myocardial function and coronary flow were significantly improved in the presence of the definitive xanthine oxidase blocker oxypurinol. Free radical concentrations measured by spin-trapping with 5,5'-dimethyl-1-pyrroline-N-oxide were significantly decreased by oxypurinol and the energetic state of the heart was improved as reflected by an increased recovery of phosphocreatine and a higher phosphocreatine/Pi ratio. ATP recovery, however, was not altered, indicating that the improved functional and metabolic state of the heart was not due to ATP salvage. Spectrophotometric assays for the enzyme showed an increase in the amount of xanthine oxidase relative to dehydrogenase following ischemia, and a total available xanthine oxidase pool in the rat heart of approximately 150 milliunits/g of protein. Thus, xanthine oxidase is a significant source of the oxidative injury which occurs upon reperfusion of the ischemic rat heart.     

C-phycocyanin protects against ischemia-reperfusion injury of heart through involvement of p38 MAPK and ERK signaling

We previously showed that C-phycocyanin (PC), an antioxidant biliprotein pigment of Spirulina platensis (a blue-green alga), effectively inhibited doxorubicin-induced oxidative stress and apoptosis in cardiomyocytes. Here we investigated the cardioprotective effect of PC against ischemia-reperfusion (I/R)-induced myocardial injury in an isolated perfused Langendorff heart model. Rat hearts were subjected to 30 min of global ischemia at 37 degrees C followed by 45 min of reperfusion. Hearts were perfused with PC (10 microM) or Spirulina preparation (SP, 50 mg/l) for 15 min before the onset of ischemia and throughout reperfusion. After 45 min of reperfusion, untreated (control) hearts showed a significant decrease in recovery of coronary flow (44%), left ventricular developed pressure (21%), and rate-pressure product (24%), an increase in release of lactate dehydrogenase and creatine kinase in coronary effluent, significant myocardial infarction (44% of risk area), and TdT-mediated dUTP nick end label-positive apoptotic cells compared with the preischemic state. PC or SP significantly enhanced recovery of heart function and decreased infarct size, attenuated lactate dehydrogenase and creatine kinase release, and suppressed I/R-induced free radical generation. PC reversed I/R-induced activation of p38 MAPK, Bax, and caspase-3, suppression of Bcl-2, and increase in TdT-mediated dUTP nick end label-positive apoptotic cells. However, I/R also induced activation of ERK1/2, which was enhanced by PC treatment. Overall, these results for the first time showed that PC attenuated I/R-induced cardiac dysfunction through its antioxidant and antiapoptotic actions and modulation of p38 MAPK and ERK1/2.     

Temporary blockade of contractility during reperfusion elicits a cardioprotective effect of the p38 MAP kinase inhibitor SB-203580

p38 MAP kinase activation is known to be deleterious not only to mitochondria but also to contractile function. Therefore, p38 MAP kinase inhibition therapy represents a promising approach in preventing reperfusion injury in the heart. However, reversal of p38 MAP kinase-mediated contractile dysfunction may disrupt the fragile sarcolemma of ischemic-reperfused myocytes. We, therefore, hypothesized that the beneficial effect of p38 MAP kinase inhibition during reperfusion can be enhanced when contractility is simultaneously blocked. Isolated and perfused rat hearts were paced at 330 rpm and subjected to 20 min of ischemia followed by reperfusion. p38 MAP kinase was activated after ischemia and early during reperfusion (<30 min). Treatment with the p38 MAP kinase inhibitor SB-203580 (10 microM) for 30 min during reperfusion, but not the c-Jun NH(2)-terminal kinase inhibitor SP-600125 (10 microM), improved contractility but increased creatine kinase release and infarct size. Cotreatment with SB-203580 and the contractile blocker 2,3-butanedione monoxime (BDM, 20 mM) or the ultra-short-acting beta-blocker esmorol (0.15 mM) for the first 30 min during reperfusion significantly reduced creatine kinase release and infarct size. In vitro mitochondrial ATP generation and myocardial ATP content were significantly increased in the heart cotreated with SB-203580 and BDM during reperfusion. Dystrophin was translocated from the sarcolemma during ischemia and reperfusion. SB-203580 increased accumulation of Evans blue dye in myocytes depleted of sarcolemmal dystrophin during reperfusion, whereas cotreatment with BDM facilitated restoration of sarcolemmal dystrophin and mitigated sarcolemmal damage after withdrawal of BDM. These results suggest that treatment with SB-203580 during reperfusion aggravates myocyte necrosis but concomitant blockade of contractile force unmasks cardioprotective effects of SB-203580.