Glucose,insulin and potassium (GIK) during reperfusion mediates improved myocardial bioenergetics

Previous studies suggest glucose, insulin and potassium (GIK) infusion during ischemia reduces infarct size and improves post-ischemic myocardial function in acute myocardial infarction and following surgical revascularization of the heart. The potential use of GIK when given only during reperfusion after a period of global ischemia, as might occur during cardiac arrest, is unclear. To test the hypothesis that GIK reperfusion improves post-ischemic myocardial bioenergetics and function, we utilized a perfused heart model. Hearts from Sprague-Dawley rats (350-450 g) were perfused at 85 mmHg with oxygenated Krebs-Henseleit bicarbonate containing 5.5 mM glucose and 0.2 mM octanoic acid. Following 20 min of global ischemia, hearts were reperfused for 30 min with original solution (control) or GIK in two different doses (10 or 20 mM glucose each with insulin 10 U/l and K(+) 7 meq/l). Hearts perfused with GIK solutions had significantly higher ATP, creatine phosphate, energy charge, and NADP(+) and lower AMP and inosine levels compared with control after 30 min of reperfusion. Hearts reperfused with GIK had significantly higher developed pressure and higher dP/dt than control reperfused hearts. Reperfusion with GIK improved post-ischemic recovery of both contractile function and the myocardial bioenergetic state. GIK may be a viable adjunctive reperfusion therapy following the global ischemia of cardiac arrest to improve post-resuscitation cardiac dysfunction.     

Effect of nifedipine in hypothermic cardioplegia: a phosphorus-31 nuclear magnetic resonance study

The ability of nifedipine to enhance myocardial protection was assessed on isolated perfused rat hearts subjected to 180 min of hypothermic (20 degrees C), global ischemia, followed by 45 min of normothermic reperfusion. Intracellular pH, ATP, Pi and phosphocreatine content were serially measured at 4 min intervals by phosphorus-31 nuclear magnetic resonance spectroscopy and correlated with simultaneously recorded hemodynamic parameters. Addition of nifedipine (0.075 mumol/l and 0.5 mumol/l) to Saint Thomas' cardioplegic solution reduced Pi accumulation during ischemic arrest and increased phosphocreatine levels during reperfusion. Post-ischemic functional recovery was not improved at a drug concentration of 0.075 mumol/l and was depressed at 0.5 mumol/l. These results clearly show that the presence of nifedipine in Saint Thomas' cardioplegic solution does not provide significant additional myocardial protection under hypothermic conditions.     

Myocardial preservation: a comparison of oxygenated crystalloid and blood cardioplegia

The purpose of this experiment was to compare myocardial protective effect after global ischemia using oxygenated crystalloid (CCcO2) and an oxygenated blood (BCcO2) cardioplegic solutions. Post-ischemic ventricular performance was studied in 2 equal (n = 7) groups of dogs subjected to 120 min of global ischemia induced at average myocardial temperatures of 8 degrees C in the CCcO2 group and 18 degrees C in the BCcO2 group. Left ventricular (LV) function included analysis of LV systolic function (global and regional function), LV diastolic function (chamber and myocardial stiffness) and LV relaxation was measured by sonomicrometry and Millar micrometers. Data were processed with a Dec PDP-11/23 computer. In vitro oxygen content (Vol%) measured 3.2 +/- 1.0 (CCcO2) and 9.5 +/- 0.3 (BCcO2). Percent recoveries of LV global function (LVSP, loop area, % shortening, LV dp/dt, mean VCF and E max) in the CCcO2 group were approximately the same as those in the BCcO2 group. There were no significant differences in LV regional function (loop area and % shortening) after ischemia between the two groups. The chamber and myocardial stiffness after ischemia in the CCcO2 group were almost the same as the baseline values. Values in the BCcO2 group were reduced significantly compared to the baseline level. There were significant differences in post-ischemic chamber and myocardial stiffness between the two groups. Post-ischemic maximum negative LV dp/dt in both groups decreased significantly compared to the baseline values. However, the time constant and diastolic interval after ischemia in both groups were approximately the same as the baseline values. We conclude that there were no significant differences in myocardial protective effect between the CCcO2 and BCcO2 groups, and both methods preserved the ischemic myocardium well.     

Reversible blockade of electron transport during ischemia protects mitochondria and decreases myocardial injury following reperfusion

Cardiac mitochondria sustain damage during ischemia and reperfusion, contributing to cell death. The reversible blockade of electron transport during ischemia with amobarbital, an inhibitor at the rotenone site of complex I, protects mitochondria against ischemic damage. Amobarbital treatment immediately before ischemia was used to test the hypothesis that damage to mitochondrial respiration occurs mainly during ischemia and that protection of mitochondria during ischemia leads to decreased cardiac injury with reperfusion. Langendorff-perfused Fischer-344 rat hearts were treated with amobarbital (2.5 mM) or vehicle for 1 min immediately before 25 min of global ischemia. Both groups were reperfused for 30 min without additional treatment. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated after reperfusion. Ischemia and reperfusion decreased state 3 and increased state 4 respiration rate in both SSM and IFM. Amobarbital treatment protected oxidative phosphorylation measured following reperfusion and improved the coupling of respiration. Cytochrome c content measured in SSM and IFM following reperfusion decreased in untreated, but not in amobarbital-treated, hearts. H(2)O(2) release from SSM and IFM isolated from amobarbital-treated hearts during reperfusion was markedly decreased. Amobarbital treatment before ischemia improved recovery of contractile function (percentage of preischemic developed pressure: untreated 51 +/- 4%, n = 12; amobarbital 70 +/- 4%, n = 11, p < 0.01) and substantially reduced infarct size (untreated 32 +/- 2%, n = 7; amobarbital 13 +/- 2%, n = 7, p < 0.01). Thus, mitochondrial damage occurs mainly during ischemia rather than during reperfusion. Reperfusion in the setting of preserved mitochondrial respiratory function attenuates the mitochondrial release of reactive oxygen species, enhances contractile recovery, and decreases myocardial infarct size.     

Protection against ischemia/reperfusion injury and myocardial dysfunction by antisense-oligodeoxynucleotide directed at angiotensin-converting enzyme mRNA.

Angiotensin-converting enzyme (ACE) activity in the myocardium and angiotensin-II (Ang-II) levels in plasma increase after myocardial ischemia, which lead to exacerbation of myocardial injury and cardiac dysfunction. We examined the protective role of novel antisense-oligodeoxynucleotide (AS-ODN) directed at ACE mRNA in myocardial ischemic injury. Sprague-Dawley rats were treated with ACE-AS-ODN (200 microg per rat, n = 8, i.v.) or inverted-ODN (IN-ODN, 200 microg per rat, n = 8, i.v.), given with 600 microg per rat of liposome DOTAP/DOPE. Hearts from AS-ODN- or IN-ODN-treated rats were excised, perfused in vitro, and subjected to 25 min of global ischemia followed by 30 min of reperfusion. Parallel groups of rats were given ACE inhibitor captopril (5 mg/kg, n = 8) or saline (n = 8) before excising the hearts. Ischemia/reperfusion resulted in myocardial dysfunction (increase in coronary perfusion pressure and LV end-diastolic pressure and a decrease in developed LV pressure) in the saline-treated rats. Myocardial dysfunction was associated with evidence of lipid peroxidation and enzyme leakage (MDA and LDH levels in the myocardium) and up-regulation of ACE protein expression. Administration of AS-ODN or captopril, but not IN-ODN, reduced Ang-II levels in the plasma, decreased ischemia/reperfusion-mediated cardiac functional deterioration and lipid peroxidation, and preserved LDH in the myocardium (all P < 0.05 versus the saline group). AS-ODN and captopril had equipotent effects on cardiac dynamics. ACE protein expression (western blot) was decreased in the hearts of the AS-ODN-treated group, but not in IN-ODN-treated rat hearts. In contrast, ACE protein expression was significantly increased in captopril-treated rat hearts. These observations suggest that AS-ODN directed at ACE mRNA can ameliorate myocardial dysfunction and injury after ischemia/reperfusion, and its use is associated with decreased expression of ACE protein in the ischemic myocardium.     

Cyclocreatine protects against ischemic injury and enhances cardiac recovery during early reperfusion

ABSTRACT

Introduction: A critical mechanism of how hypoxia/ischemia causes irreversible myocardial injury is through the exhaustion of adenosine triphosphate (ATP). Cyclocreatine (CCr) and its water-soluble salt Cyclocreatine-Phosphate (CCrP) are potent bioenergetic agents that preserve high levels of ATP during ischemia.

Areas covered: CCr and CCrP treatment prior to the onset of ischemia, preserved high levels of ATP in ischemic myocardium, reduced myocardial cell injury, exerted anti-inflammatory and anti-apoptotic activities, and restored contractile function during reperfusion in animal models of acute myocardial infarction (AMI), global cardiac arrest, cardiopulmonary bypass, and heart transplantation. Medline and Embase (1970 – Feb 2019), the WIPO databank (up to Feb 2019); no language restriction.

Expert opinion: This review provides the basis for a number of clinical applications of CCrP and CCr to minimize ischemic injury and necrosis. One strategy is to administer CCrP to AMI patients in the pre-hospital phase, as well as during, or after Percutaneous Coronary Intervention (PCI) procedure to potentially achieve protection of the myocardium, reduce infarcted-size, and, thus, limit the progression to heart failure. Another clinical applications are in predictable myocardial ischemia where pretreatment with CCrP would likely improve outcome and quality of life of patients who will undergo cardiopulmonary bypass for coronary revascularization and end-stage heart failure patients scheduled for heart transplantation.     

A peroxynitrite decomposition catalyst: FeTPPS confers cardioprotection during reperfusion after cardioplegic arrest in a working isolated rat heart model

Heart transplant is considered to be an extremely severe ischemia-reperfusion sequence. Post-ischemic dysfunction triggers multiple processes especially oxidative stress, but the mechanisms remain unclear. Free radical interactions lead to peroxynitrite generation, which seems to be involved in early post-transplant heart failure. The aim of this study was to evaluate the potential impact of a peroxynitrite decomposition catalyst: FeTPPS (5,10,15,20-tetrakis-[4-sulfonatophenyl]-porphyrinato-fer[III]) and pyruvate on myocardial functional recovery after cardioplegic arrest using an experimental protocol in rat hearts. Isolated working rat hearts were subjected to ischemia (4 h at 4 degrees C in cardioplegic solutions), followed by 45 min of reperfusion. Four groups were constituted: control, pyruvate: (2 mm) added to cardioplegic and Ringer-lactate solutions, FeTPPS: (10 microm) perfused during the reperfusion, and a combination of both treatments. Lactate dehydrogenase (LDH) activity was assessed during the reperfusion to evaluate the level of cardiac injury. Oxidative stress was evaluated on heart slices using a fluorescent probe: dihydroethidium, and the collagen content was assessed using picro-Sirius coloration. Global post-ischemic recovery in the control group was about 35% of pre-ischemic values. Results showed that addition of pyruvate led to an increase in myocardial function and to a decrease in LDH activity released during the reperfusion. FeTPPS protected against injury after cardioplegic arrest during reperfusion. No additive effect of the two treatments (pyruvate + FeTPPS) was observed. The collagen content was better preserved in the FeTPPS group than in the control and pyruvate groups. In conclusion, this study shows that peroxynitrite plays an important role in the functional and cellular alterations associated with cardiac ischemia-reperfusion sequences and confirms that pyruvate helped to preserve myocardial function. The use of the peroxynitrite decomposition catalyst (FeTPPS) may help to improve myocardial preservation during a prolonged ischemia sequence.     

Overexpression of the rat inducible 70-kD heat stress protein in a transgenic mouse increases the resistance of the heart to ischemic injury.

Myocardial protection and changes in gene expression follow whole body heat stress. Circumstantial evidence suggests that an inducible 70-kD heat shock protein (hsp70i), increased markedly by whole body heat stress, contributes to the protection. Transgenic mouse lines were constructed with a cytomegalovirus enhancer and beta-actin promoter driving rat hsp70i expression in heterozygote animals. Unstressed, transgene positive mice expressed higher levels of myocardial hsp70i than transgene negative mice after whole body heat stress. This high level of expression occurred without apparent detrimental effect. The hearts harvested from transgene positive mice and transgene negative littermates were Langendorff perfused and subjected to 20 min of warm (37 degrees C) zero-flow ischemia and up to 120 min of reflow while contractile recovery and creatine kinase efflux were measured. Myocardial infarction was demarcated by triphenyltetrazolium. In transgene positive compared with transgene negative hearts, the zone of infarction was reduced by 40%, contractile function at 30 min of reflow was doubled, and efflux of creatine kinase was reduced by approximately 50%. Our findings suggest for the first time that increased myocardial hsp70i expression results in protection of the heart against ischemic injury and that the antiischemic properties of hsp70i have possible therapeutic relevance.     

A comparison between ranolazine and CVT-4325, a novel inhibitor of fatty acid oxidation, on cardiac metabolism and left ventricular function in rat isolated perfused heart during ischemia and reperfusion

Inhibition of fatty acid oxidation has been reported to be cardioprotective against myocardial ischemic injury; however, recent studies have questioned whether the cardioprotection associated with putative fatty acid oxidation inhibitors, such as ranolazine and trimetazidine, are due to changes in substrate oxidation. Therefore, the goals of this study were to compare the effects of ranolazine with a new fatty acid oxidation inhibitor, CVT-4325 [(R)-1-(2-methylbenzo[d]thiazol-5-yloxy)-3-(4-((5-(4-(trifluoromethyl)phenyl)-1,2,4-oxadiazol-3-yl)methyl)-piperazin-1-yl)propan-2-ol], on carbohydrate and fatty acid oxidation and on left ventricular (LV) function in the response to ischemia/reperfusion in rat isolated perfused hearts. Metabolic fluxes were determined in hearts perfused in an isovolumic Langendorff mode using 13C nuclear magnetic resonance isotopomer analysis or in isolated working hearts using [14C]glucose and [3H]palmitate, with and without 10 microM ranolazine or 3 microM CVT-4325. Isovolumic perfused hearts were also subjected to 30 min of low-flow ischemia (0.3 ml/min) and 60 min of reperfusion, and working hearts were subjected to 15 min of zero-flow ischemia and 60 min of reperfusion. Regardless of the experimental protocol, ranolazine had no effect on carbohydrate or fatty acid oxidation, whereas CVT-4325 significantly reduced fatty acid oxidation up to approximately 7-fold with a concomitant increase in carbohydrate oxidation. At these same concentrations, although ranolazine significantly improved LV functional recovery following ischemia/reperfusion, CVT-4325 had no significant protective effect. These results demonstrate that at pharmacologically relevant concentrations, ischemic protection by ranolazine was not mediated by inhibition of fatty acid oxidation and conversely that inhibition of fatty acid oxidation with CVT-4325 was not associated with improved LV functional recovery.     

脂肪乳预处理和后处理对大鼠心肌缺血/再灌注损伤的保护作用

目的 观察在心肌缺血/再灌注(I/R)损伤前(预处理)或损伤后(后处理)给予脂肪乳对心脏I/R损伤的改善作用,探讨脂肪乳在心脏保护方面的潜在价值.方法 实验采用大鼠Langendorff心脏离体灌流模型.将24只雄性SD大鼠随机分组:空白对照组(ISCH组)心脏离体平衡50 min,37 ℃缺血40 min,复灌120 min;脂肪乳预处理组(I-preC组)心脏离体平衡20 min,给予含30%的脂肪乳灌注液输注15 min,洗脱15 min,随后37 ℃缺血40 min,复灌120 min;脂肪乳后处理组(I-postC 组)心脏离体平衡50 min,37 ℃缺血40 min,复灌120 min,复灌开始即给予含30%的脂肪乳灌注液输注15 min.于平衡50 min和复灌120 min期间连续监测左室内压上升和下降最大速率(±dp/dt max)、左室舒张期末压(LVEDP)、左室舒张压(LVDP)、心率(HR).平衡20 min和复灌60 min时接取冠状动脉流出液,测定肌酸激酶(CK)和乳酸脱氢酶(LDH)的活性.复灌结束后计算心肌梗死面积.结果 心脏机械功能指标:与ISCH组比较,复灌期间I-postC组+dp/dt max、LVDP显著升高,-dp/dt max、LVEDP显著降低(P均＜0.05);而I-preC组各指标比较差异无统计学意义.冠状动脉生化指标:复灌60 min时I-preC组和I-postC组CK和LDH活性均较ISCH组显著降低(P均d＜0.05);I-preC组与I-postC组比较差异无统计学意义(尸均＞0.05).I-preC组和I-postC组心肌梗死面积较ISCH组显著降低[(21.6±1.8)%、(15.9±1.3)%比(46.5±3.9)%,P均<0.05)];I-preC组与I-postC组比较差异无统计学意义(P＞0v.05).结论 脂肪乳预处理和后处理均能减轻心肌I/R损伤后CK和LDH的释放,缩小心肌梗死面积.脂肪乳后处理能显著增强心肌I/R损伤后心脏的机械功能.     

Oxygen-derived free radicals and postischemic myocardial reperfusion: therapeutic implications

Oxygen-derived free radicals have been implicated in the pathogenesis of various disease states, including myocardial ischemia and reperfusion. In this article, we review 1) the evidence linking free radical production and myocardial injury during myocardial ischemia and reperfusion and 2) results of studies of the effects of the pharmacological therapies available potentially to prevent free radical-mediated injury. Free radicals can be produced during ischemia and reperfusion by several different biochemical pathways. Of these, the xanthine oxidase reaction and the output of free radicals by neutrophils that have accumulated in damaged tissue have been studied extensively. When produced, free radicals can potentially damage myocytes or endothelial cells through peroxidation of membrane lipids or damage to proteins or nucleic acids. Using electron spin resonance spectroscopy, several studies have shown a 'burst' of oxygen free radicals immediately after reperfusion. Moreover, exogenous generation of intravascular free radicals has been shown to produce marked vascular and myocyte damage, as well as contractile dysfunction. 'Anti-free radical' interventions, such as xanthine oxidase inhibitors and free radical scavengers have been reported to prevent contractile dysfunction and reperfusion-induced arrhythmias after an episode of reversible ischemic injury. However, after more severe episodes of ischemia, such interventions have had conflicting effects on myocardial infarct size. 'Anti-free radical' interventions could be of potential use in situations where reversible ischemic injury occurs. In situations where reperfusion is achieved after irreversible ischemic injury has occurred, the potential beneficial effect of these treatments on infarct size is more doubtful.     

The rapid and reversible activation of a calcium-independent plasmalogen-selective phospholipase A2 during myocardial ischemia.

Recent studies have demonstrated the existence of two members of a novel family of calcium-independent plasmalogen-selective phospholipases A2 in mammalian myocardium (Wolf, R. A., and R. W. Gross. 1985. J. Biol. Chem. 260:7295-7303; and Hazen, S. L., D. A. Ford, and R. W. Gross. 1991. J. Biol. Chem. 266:5629-5633). To examine the potential role of these calcium-independent phospholipases A2 in mediating membrane dysfunction during early myocardial ischemia, the temporal course of alterations in phospholipase A2 activity during global ischemia in Langendorf perfused rabbit hearts was quantified and compared with traditionally accepted markers of myocytic ischemic injury and anaerobic metabolism. We now report that membrane-associated calcium-independent plasmalogen-selective phospholipase A2 activity increased over 400% during 2 min of global ischemia (P less than 0.01), was near maximally activated (greater than 10-fold) after only 5 min of ischemia, and remained activated throughout the entire ischemic interval examined (2-60 min). Activation of membrane-associated plasmalogen-selective phospholipase A2 after 5 min of myocardial ischemia was rapidly reversible during reperfusion of ischemic tissue. Both the activation of phospholipase A2 and its reversibility during reperfusion were temporally correlated to alterations in myocytic anaerobic metabolism. Furthermore, activation of membrane-associated phospholipase A2 was essentially complete before electron microscopic evidence of cellular damage. Collectively, these results identify dynamic alterations in calcium-independent plasmalogen-selective phospholipase A2 activity during myocardial ischemia which precede irreversible cellular injury and demonstrate that activation of plasmalogen-selective phospholipase A2 is amongst the earliest biochemical alterations in ischemic myocardium.     

The “No-Reflow” Phenomenon after Temporary Coronary Occlusion in the Dog

The role of microvascular damage in the genesis of the "no-reflow" phenomenon was investigated in the left ventricular myocardium of dogs subjected to temporary occlusions of a major coronary artery for 40 and 90 min. Intravenous carbon black or thioflavin S (a fluorescent vital stain for endothelium) were used to demonstrate the distribution of coronary arterial flow in control and damaged myocardium. These tracers were injected simultaneously with release of the coronary occlusion or after 5 or 20 min of reflow of coronary arterial blood. After 40 min of ischemia plus arterial reperfusion, usually the tracers were evenly distributed throughout the damaged tissue at each time of reperfusion. On the other hand, when reflow was allowed after 90 min of ischemia, portions of the inner half of damaged myocardium were not penetrated by the tracers. Electron microscopic study of this poorly perfused tissue revealed severe capillary damage; endothelial cells with large intraluminal protrusions and decreased pinocytic vesicles were common. Also, occasional intraluminal fibrin thrombi were noted, as well as extravascular fibrin deposits and erythrocytes. Myocardial cells were swollen in both poorly perfused and well-perfused irreversibly injured tissue. Contraction bands and mitochondrial Ca(2+) accumulation were prominent features of irreversible injury with reflow at 40 min but were not noted after 90 min of ischemia in areas with poor perfusion. These results suggest that 40 min of ischemia were tolerated by the capillary bed of the dog heart without serious capillary damage or perfusion defects, but that 90 min of ischemic injury was associated with the "no-reflow" phenomenon, i.e., failure to achieve uniform reperfusion. This failure of reflow was associated with extensive capillary damage and myocardial cell swelling. Death of severely ischemic myocardial cells in this model occurs before the onset of capillary damage and the no-reflow phenomenon.     

The effectiveness of postischemic oxypurinol administration upon myocardial function in the isolated rat heart

The Langendorff isolated rat heart preparation was used to determine the effect of oxypurinol, a xanthine oxidase inhibitor, on myocardial function when administered during reperfusion after 30 min of warm ischemia. Twenty rats were randomly sorted into 2 groups of 10, and an isolated heart preparation made from each rat. The isolated hearts were perfused for 15 min with a modified Krebs-Henseleit solution to permit stabilization of the preparation. Each heart was then subjected to 30 min of total ischemia at 37 degrees C followed by 40 min of reperfusion with either saline-treated perfusate or oxypurinol-treated perfusate (1.3 mM). The maximum power produced and the preload required to produce maximum power were both determined prior to ischemia and every 10 min after ischemia during 40 min of reperfusion. The saline-treated group, but not the oxypurinol-treated group, showed significantly less maximum power output at all testing times during reperfusion compared to the preischemic value (P less than 0.05). There was a significantly greater maximum power output (P less than 0.02) in the oxypurinol-treated group compared to the saline-treated group after 20, 30, and 40 min of reperfusion. There were no differences within either group, or between groups, for the preload required to produce maximum power at any of the testing times. Ultrastructural examination of myocardium after reperfusion showed severe mitochondrial and myofibrillar disruption in the saline-treated group but not in the oxypurinol-treated group. We conclude that oxypurinol administered following 30 min of total ischemia at the onset of reperfusion, can preserve myocardial function during the early reperfusion period in the isolated rat heart.     

参附注射液对缺血再灌注心肌损伤的保护作用

目的：探讨参附注射液对缺血／再灌注（I／R）损伤心肌的保护作用及其机制。方法：32只雄性SD大鼠随机分为4组：正常对照组（n=8）、缺血／再灌注组（n=8）、参附注射液30mg／L组（n=8）和100mg／L组（n=8）。采用Langendorff离体心脏灌流模型，制备心肌缺血再灌注损伤模型，在心脏缺血前和再灌注后，给予参附注射液，观察离体大鼠心脏血流动力学指标和心肌组织中的高能磷酸化舍物ATP含量、MDA含量及SOD活性等的变化。结果：参附注射液100mg／L明显改善缺血／再灌注后心脏血流动力学指标。缺血／再灌注组大鼠心肌ATP含量和SOD活性明显降低，MDA含量明显升高。与缺血／再灌注组比较，参附注射液30mg／L组和100mg／L组心肌MDA值减少（P〈O．05），SOD值升高（P〈0．05）；参附注射液100mg／L组ATP含量增加（P〈0．05）。结论：参附注射液能通过提高心肌组织ATP含量和SOD活性，减少MDA含量，改善缺血／再灌注后心脏血流动力学紊乱，减轻大鼠心肌缺血再灌注损伤。     

Blockade of electron transport before cardiac ischemia with the reversible inhibitor amobarbital protects rat heart mitochondria

Cardiac ischemia damages the mitochondrial electron transport chain. Irreversible blockade of electron transport at complex I by rotenone decreases ischemic damage to cardiac mitochondria by decreasing the loss of cytochrome c and preserving respiration through cytochrome oxidase. Therapeutic intervention to protect myocardium during ischemia and reperfusion requires the use of a reversible inhibitor that allows resumption of oxidative metabolism during reperfusion. Amobarbital is a reversible inhibitor at the rotenone site of complex I. We asked whether amobarbital administered immediately before ischemia protected respiratory function. Isolated rat hearts were perfused for 15 min followed by 25-min global ischemia at 37 degrees C. Amobarbital-treated hearts received drug for 1 min before ischemia. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated after ischemia, and oxidative phosphorylation was measured. Amobarbital protected oxidative phosphorylation, including through cytochrome oxidase, in both SSM and IFM in a dose-dependent manner, with an optimal dose of 2 to 2.5 mM. Amobarbital also preserved cytochrome c content in both SSM and IFM. Thus, reversible blockade of the electron transport chain during ischemia protects mitochondrial respiration.     

三十烷醇对大鼠离体心脏缺血再灌注损伤的影响

【目的】观察三十烷醇（triacontanol ,TRIA）对心肌缺血再灌注损伤（IRI）的影响。【方法】采用Langendorff灌流装置建立大鼠离体心脏IRI模型。将大鼠随机分为正常组、缺血再灌注（IR）组、不同剂量T RIA＋IR组及T RIA （2．5μg/mL）组。正常组全心持续灌流90 min;IR组平衡灌注30 min ,缺血30 min后再灌注30 min;TRIA＋IR组在缺血前5 min分别给予（25,15,5,2．5）μg/mL TRIA之后处理同IR组;TRIA组平衡灌注30 min后给药5 min ,之后持续灌流30 min。观测各组心率（HR）、冠脉流量（CF）、左室内压（LVP）和左室内压变化最大速率（± dp/dtmax）,测定冠脉流出液中肌酸激酶（CK）释放量。【结果】与正常组比较,IR组引起明显的心功能损伤,表现为再灌注期间 HR、CF、LVP、± dp/dtmax降低以及CK释放量增加;心脏灌注不同剂量TRIA（25,15,5,2．5μg/mL）5 min可加重IRI所致心功能损伤,甚至心脏停跳,表现为LVP、± dp/dtmax进一步降低,CF显著减少,HR减慢以及CK释放量增加;单独灌注TRIA（2．5μg/mL）对大鼠心功能也有明显抑制作用,抑制作用持续30 min不能恢复。【结论】离体大鼠心脏灌流 T RIA可抑制心功能及加重心肌IR后心功能的损伤。     

Possible involvement of PKC-δ in the abrogated cardioprotective potential of ischemic preconditioning in hyperhomocysteinemic rat hearts

The present study has been designed to investigate the possible role of protein kinase C-delta (PKC-δ) in hyperhomocysteinemia-induced attenuation of cardioprotective potential of ischemic preconditioning (IPC). Rats were administered l-methionine (1.7 g/kg/day, p.o.) for 4 weeks to produce hyperhomocysteinemia. Isolated Langendorff perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30 min followed by reperfusion for 120 min. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride (TTC) staining. Coronary effluent was analyzed for lactate dehydrogenase (LDH) and creatine kinase (CK) release to assess the degree of cardiac injury. Moreover, the oxidative stress in heart was assessed by measuring lipid peroxidation and superoxide anion generation. The ischemia-reperfusion (I/R) was noted to produce myocardial injury as assessed in terms of increase in myocardial infarct size, LDH and CK in coronary effluent and oxidative stress in normal and hyperhomocysteinemic rat hearts. In addition, the hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with high degree of oxidative stress as compared with normal rat hearts subjected to I/R. Four episodes of IPC (5 min each) afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts as assessed in terms of reduction in myocardial infarct size, LDH, CK and oxidative stress. On the other hand, IPC mediated myocardial protection against I/R-injury was abolished in hyperhomocysteinemic rat hearts. Treatment with rottlerin (10 μM), a selective inhibitor of PKC-δ did not affect the cardioprotective effects of IPC in normal rat hearts; but its treatment significantly restored the cardioprotective potentials of IPC in hyperhomocysteinemic rat hearts. The high degree of oxidative stress produced in hyperhomocysteinemic rat hearts during reperfusion may activate PKC-δ, which may be implicated in the observed paradoxically abrogated cardioprotective potentials of IPC in hyperhomocysteinemic rat hearts.     

Early postoperative function of the heart after coronary artery bypass grafting is not predicted by myocardial necrosis and glutathione-associated oxidative stress

BACKGROUND: To investigate whether cardioplegia-related myocardial necrosis, lactate and glutathione release are predictive for early postoperative cardiac function after coronary artery bypass grafting (CABG). METHODS: Twelve patients with stabile angina scheduled for elective CABG were included. Myocardial release of troponin I (Tn I), creatine kinase MB isoenzyme mass (CK-MB), oxidized glutathione (GSSG) and lactate in blood were measured before cardioplegia, and up to 20 min thereafter. Cardiac function was assessed for 12 postoperative hours. RESULTS: Release of Tn I and CK-MB peaked at 20 min (-14.5+/-24.1 ng/ml and -23.9+/-30.6 ng/ml, respectively) and lactate at 1 min of reperfusion (-1.5+/-0.6 mmol/l). Significant GSSG release occurred at 5 min, with concomitant increase of glutathione redox ratio. The changes were not correlated to ischemic time. Cardiac index was increased after CPB and remained higher than preoperative value until the first postoperative morning. No correlations between postcardioplegic heart function and markers of tissue injury were found. CONCLUSIONS: The extent of myocardial reversible and irreversible injury does not predict early postoperative contractile function of the heart.     

Postischemic inotropic support of the dysfunctional heart

OBJECTIVE: To determine relative adenine nucleotide regeneration and improvement in left ventricular (LV) function using three commonly used adrenergic agents--epinephrine, dobutamine, and phenylephrine---during reperfusion after a period of global ischemia. After initial resuscitation from cardiac arrest, adrenergic agents are frequently required to support postischemic LV dysfunction. However, the relative effectiveness and associated bioenergetic changes associated with these agents in the postischemic heart are unclear. DESIGN: Prospective, controlled laboratory study. SETTING: University research laboratory. SUBJECTS: Isolated, perfused Sprague-Dawley rat hearts. INTERVENTIONS: After 20 mins of global ischemia, isolated rat hearts were reperfused for 30 mins with Krebs-Henseleit solution alone (control, n = 8), or with the addition of equipotent doses of epinephrine 1 microM (n = 8), dobutamine 0.3 microM (n = 8), or phenylephrine 50 microM (n = 8). In a second experiment, an alpha-1 antagonist, prazosin was given with phenylephrine to block the presumed alpha-1 agonist effect of phenylephrine. MEASUREMENTS AND MAIN RESULTS: A constant volume balloon was placed in the left ventricle to measure LV pressure and derived parameters of LV function. Adenine nucleotide concentrations were derived at various time points using high-performance liquid chromatography. During reperfusion, the phenylephrine group had significant improvement in LV function and cardiac efficiency in contrast to epinephrine and dobutamine. Total adenine nucleotides tended to be highest in the phenylephrine group with significant increases in adenosine diphosphate and adenosine monophosphate and no significant loss of adenosine triphosphate. The phenylephrine-induced increase in heart rate and developed pressure could be blocked with an alpha-1 antagonist, prazosin. CONCLUSIONS: In the isolated reperfused heart, phenylephrine, mediated by alpha-1 agonism, significantly improves postischemic LV dysfunction without worsening the overall myocardial metabolic state.