缺血后适应心肌线粒体能量代谢研究

目的研究缺血后适应心肌线粒体能量代谢特点。方法以Langendofff离体心脏灌注系统构建缺血后适应大鼠模型,随机分为对照组．再灌注组和后适应组,每组16只。平衡20min后,对照组灌注60min;再灌注组停灌30min,再灌注30min;后适应组停灌30min之后,循环6次再灌注10s,停灌10s,再灌注28min。记录心率和冠状动脉流量。冉灌注末取心肌．用高效液相色谱法测定高能磷酸化合物三磷腺苷、二磷腺苷和一磷腺苷含量;用差速离心法提取心肌线粒体,用氧电极法测定线粒体3态呼吸、4态呼吸和线粒体呼吸控制率。结果与再灌注组比较,后适应组明显提高再灌注末的心率和冠状动脉流量,明显提高心肌内二磷腺苷和一磷腺苷含量,三磷腺苷在各组差异无统计学意义。线粒体3态呼吸和线粒体呼吸控制率改善。结论心肌线粒体能量代谢改善,是缺血后适应心肌保护的可能机制之一。     

Effect of reperfusion late in the phase of reversible ischemic injury. Changes in cell volume, electrolytes, metabolites, and ultrastructure

The acute effects of reperfusion on myocardium reversibly damaged by 15 minutes of severe ischemia in vivo, were studied. Changes in the adenine nucleotide pool, cell volume regulation, myocardial calcium, and ultrastructure were studied at the end of 15 minutes of ischemia and after 0.5, 3.0, and 20 minutes of reflow. Before reperfusion, adenosine triphosphate and the adenylate pool decreased by 63% and 44% of control, respectively, and the adenylate charge was reduced to 0.65. After 3 minutes of reperfusion, the adenylate charge was restored to control by the rephosphorylation of adenosine mono- and diphosphate, but adenosine triphosphate was still reduced by 45%. Mild tissue edema was detected after 0.5 minute of reflow and persisted throughout 20 minutes of reperfusion. The increased tissue water was accompanied by a slight increase in sodium and a marked increase in tissue potassium. Although massive calcium accumulation develops when irreversibly injured tissue is reperfused, no calcium overload was detected during early reperfusion of reversibly injured myocytes. Reperfusion for 3 minutes exaggerated the mitochondrial swelling induced by 15 minutes of ischemia but after 20 minutes of reperfusion, myocardial ultrastructure was essentially normal except for rare swollen, or disrupted, mitochondria. Thus, the cellular abnormalities associated with brief periods of ischemia persist for variable periods of time after reperfusion of reversibly injured myocytes. First: although adenine nucleotide repletion occurs very slowly, the adenylate charge was restored after 3 minutes, indicating rapid resumption of mitochondrial adenosine triphosphate production. Second: calcium overload was not detected, but myocardial edema and increased potassium persisted throughout the 20 minutes of reperfusion. Third: the ultrastructural consequences of ischemia were nearly reversed after 20 minutes of reperfusion.     

Impact of carvedilol on the mitochondrial damage induced by hypoxanthine and xantine oxidase--what role in myocardial ischemia and reperfusion?

OBJECTIVES: The cardioprotective effects of carvedilol (CV) may be explained in part by interactions with heart mitochondria. The objective of this work was to study the protection afforded by CV against oxidative stress induced in isolated heart mitochondria by hypoxanthine and xanthine oxidase (HX/XO), a well-known source of reactive oxygen species (ROS) in the cardiovascular system. METHODS: Mitochondria were isolated from Wistar rat hearts (n = 8) and incubated with HX/XO in the presence and in the absence of calcium. Several methods were used to assess the protection afforded by CV: evaluation of mitochondrial volume changes (by measuring changes in the optical density of the mitochondrial suspension), calcium uptake and release (with a fluorescent probe, Calcium Green 5-N) and mitochondrial respiration (with a Clark-type oxygen electrode). RESULTS: CV decreased mitochondrial damage associated with ROS production by HX and XO, as verified by the reduction of mitochondrial swelling and increase in mitochondrial calcium uptake. In the presence of HX and XO, CV also ameliorated mitochondrial respiration in the active phosphorylation state and prevented decrease in the respiratory control ratio (p < 0.05) and in mitochondrial phosphorylative efficiency (p < 0.001). CONCLUSIONS: The data indicate that CV partly protected heart mitochondria from oxidative damage induced by HX and XO, which may be useful during myocardial ischemia and reperfusion. It is also suggested that mitochondria may be a priority target for the protective action of some compounds.     

Cardioprotection and altered mitochondrial adenine nucleotide transport

It is becoming increasingly clear that mitochondrial dysfunction is critically important in myocardial ischemic injury, and that cardioprotective mechanisms must ultimately prevent or attenuate mitochondrial damage. Mitochondria are also essential for energy production, and therefore prevention of mitochondrial injury must not compromise oxidative phosphorylation during reperfusion. This review will focus on one mitochondrial mechanism of cardioprotection involving inhibition of adenine nucleotide transport across the outer mitochondria membrane under de-energized conditions. This slows ATP hydrolysis by the mitochondria, and would be expected to lower mitochondrial membrane potential during ischemia, to inhibit calcium uptake during ischemia, and potentially to reduce free radical generation during early reperfusion. Two interventions that similarly inhibit mitochondrial adenine nucleotide transport are Bcl-2 overexpression and GSK inhibition. A possible final common mechanism shared by both of these interventions is discussed.     

Carvedilol: relation between antioxidant activity and inhibition of the mitochondrial permeability transition.

OBJECTIVES: The mitochondrial permeability transition (MPT) is an event related to severe oxidative stress (for example, during myocardial ischemia and reperfusion) and excessive mitochondrial calcium accumulation, also being implicated in cell death. In this study, we compared the effect of carvedilol on the cardiac MPT induced by calcium and phosphate (Ca/Pi) and calcium/carboxyatractyloside (Ca/Catr). Oxidative stress plays a major role in MPT induction by Ca/Pi, leading to the oxidation of protein thiol groups, in contrast with Ca/Catr, where such oxidation is secondary to MPT induction and is not caused by oxidative stress. MATERIALS AND METHODS: Mitochondria were isolated from rat hearts and parameters related to MPT induction were evaluated (n = 5 for each inducer): mitochondrial swelling and oxidation of protein thiol groups (both measured by spectrophotometry). RESULTS: Using Ca/Pi, carvedilol protected mitochondria from MPT induction, particularly in its high conductance form. Its effect was demonstrated by analyzing the decrease in mitochondrial swelling amplitude. Simultaneously, we observed inhibition of protein thiol group oxidation (p < 0.001). By contrast, carvedilol did not show any protective effect with Ca/Catr. CONCLUSIONS: Carvedilol was only effective against the MPT when the oxidation of protein thiol groups was the cause and not the consequence of the MPT phenomenon. The results clearly show that during myocardial aggressions (ischemia and reperfusion, for example), the protective effect of carvedilol is primarily due to an antioxidant mechanism, inhibiting the production and effects of reactive oxygen species.     

Beneficial effect of fructose-1,6-bisphosphate on mitochondrial function during ischemia-reperfusion of rat liver

Several groups have reported that administration of fructose-1,6-bisphosphate (FBP) reduces ischemic injury. The aim of this study was to determine the protective effect of FBP on the impairment of mitochondrial oxidative phosphorylation by ischemia-reperfusion injury in the rat liver. The respiratory control ratio (RCR) and the adenine nucleotide content of mitochondria isolated from ischemic and reperfused livers with or without FBP treatment were measured. In FBP-treated livers, the cellular adenosine triphosphate level was restored to more than 50% of normal after 120 minutes of reperfusion following 120 minutes of ischemia, whereas that of control livers only reached 15% of normal. The RCR and the adenine nucleotide content of mitochondria isolated from FBP-treated livers were significantly higher than those of mitochondria from control livers after ischemia and reperfusion. FBP strongly suppressed the formation of lipid peroxides during reperfusion. In vitamin E-deficient rats, the RCR decreased markedly during reperfusion, but FBP protected the mitochondria against reperfusion injury. FBP has a protective effect against ischemia-reperfusion injury on the liver and especially preserves the oxidative phosphorylation capacity of hepatic mitochondria.     

Effect of ischemia-reperfusion on heart mitochondria from hyperthyroid rats

OBJECTIVE: We investigated the effect of hyperthyroidism on the functional response of mitochondria to ischemia-reperfusion and its relationship with changes in mitochondrial susceptibility to stress conditions. METHODS: Hyperthyroidism was elicited by ten daily intraperitoneal injections of T3 (10 microg/100 g body weight). Mitochondria were isolated at 3000xg (M3) from homogenates of hearts perfused by the Langendorff technique after either 25 min reperfusion following 20 min ischemia or 45 min perfusion (controls). Rates of O2 consumption and H2O2 release with complex II-linked substrate, capacity to remove H2O2, extent of oxidative damage, levels of liposoluble antioxidants, such as ubiquinols and vitamin E, and susceptibility to Ca2+ -induced swelling were determined. RESULTS: During reperfusion, hyperthyroid hearts displayed a significant tachycardia together with a low functional recovery. In comparison to the respective controls, mitochondria from both euthyroid and hyperthyroid hearts subjected to ischemia-reperfusion protocol exhibited decreases in the rate of O2 consumption, capacity to remove H2O2, and concentration of antioxidants, and increases in the rate of H2O2 release, concentration of hydroperoxides and protein-bound carbonyls, and susceptibility to Ca2+ -induced swelling. Such changes were higher in mitochondria from hyperthyroid hearts. The increase in the protein percent content and cytochrome oxidase activity of a mitochondrial fraction isolated at 8000xg (M8) from hyperthyroid hearts after reperfusion, suggests that the decline of mitochondrial respiration of M3 fraction could be due to the degradation of the oldest, mature mitochondria endowed of high oxidative capacity, but low antioxidant capacity, which would be lost by heavy mitochondrial fraction and recovered in the light fraction. CONCLUSIONS: The higher susceptibility to ischemia-reperfusion of the heart from hyperthyroid animals is associated with a significant increase in mitochondrial dysfunction.     

Sodium accumulation during ischemia induces mitochondrial damage in perfused rat hearts

OBJECTIVE: The present study aimed to elucidate the involvement of sodium overload and following damage to mitochondria during ischemia in the genesis of ischemia/reperfusion injury of perfused rat hearts. METHODS: Isolated, perfused hearts were exposed to different durations (15-35 min) of ischemia followed by 60-min reperfusion. At the end of ischemia or reperfusion, myocardial sodium and calcium contents and myocardial high-energy phosphates were determined. The cardiac mitochondrial ability to produce ATP was measured using saponin-skinned bundles. The effects of sodium on the mitochondrial membrane potential and the oxidative phosphorylation rate were examined using isolated mitochondria from normal hearts. RESULTS: Post-ischemic recovery of left ventricular developed pressure decreased in an ischemic duration-dependent manner. Ischemia induced an increase in myocardial sodium, but not calcium. This increase was dependent on the duration of ischemia. The oxygen consumption rate of skinned bundles from the ischemic heart decreased at the end of ischemia. Incubation of mitochondria with various concentrations of sodium chloride or sodium lactate in vitro resulted in a depolarization of mitochondrial membrane potential and a decrease in ATP-generating activity. This decrease was not restored after elimination of sodium compounds. CONCLUSIONS: The present findings suggest that ischemia induces an increase in sodium influx from the extracellular space and that accumulated sodium may induce irreversible damage to mitochondria during ischemia. This mitochondrial dysfunction may be one of the most important determinants for the genesis of ischemia/reperfusion injury in perfused rat hearts.     

肾脏缺血后处理对兔急性缺血再灌注心肌细胞凋亡和Bcl-2、Bax蛋白表达的影响

目的研究肾脏缺血后处理对兔急性缺血再灌注心肌细胞凋亡的影响,并探讨其保护机制。方法24只新西兰大白兔随机分为3组,每组8只。（1）缺血再灌注组（IR组）：结扎左冠状动脉前降支1h,再灌注6h。（2）肾脏缺血后处理组（RI-Post组）：操作同IR组,在再灌注即刻用动脉血管夹反复夹闭左侧肾动脉（阻断30S,再通30S,重复3次）,再灌注6h。（3）药物干预组（MI组）：结扎左冠状动脉前降支1h,再灌注前10min给予蛋白激酶C抑制剂-GF109203X（O．05mg／kg）耳缘静脉注射持续10min,再灌注即刻行RI-Post组操作,最后心肌再灌注直至6h。实验结束,采用Tunel法检测24只兔梗死区的心肌细胞凋亡,用免疫组化法检测Bax和Bcl-2蛋白在心肌细胞中的表达水平。结果肾脏缺血后处理组与对照组和药物干预组比较,心肌细胞凋亡指数明显减少（P〈0．05）,Bcl-2表达明显增多（P〈0．01）,Bax表达明显减少（P〈0．05）;而药物干预组与对照组相比各检测指标无明显差别（P〉0．05）。结论肾脏缺血后处理可减少急性缺血再灌注后心肌细胞凋亡,并影响Bcl-2、Bax蛋白的表达,从而对缺血心肌产生保护作用,其保护机制可能与激活蛋白激酶C有关。     

Regional and systemic platelet function is altered by myocardial ischemia-reperfusion

Structured Abstract Background: Myocardial reperfusionafter short durations of ischemia causes prolonged contractile dysfunction (myocardial stunning). Recently it has also been suggested that ischemia-reperfusion results in impaired coronary endothelial function. Since platelet function is, in part, regulated by an intact functioning endothelium, platelet function could be expected to change during ischemiareperfusion. However, the effect of ischemia and reperfusion on regional and systemic platelet function is unknown. The purpose of this study was to determine the effect of a brief period of myocardial ischemia followed by reperfusion on regional and systemic platelet function.Methods: Fourteen swine in an open-chest model underwent left anterior descending coronary artery (LAD) occlusion for 15 minutes followed by 120 minutes of reperfusion. Platelet aggregability in response to 5 M ADP was determined simultaneously in the femoral (systemic; N=14) and great cardiac (regional; N=9) venous blood at baseline, during occlusion, and at 40 and 90 minutes after reperfusion. LAD blood flow and regional myocardial function were determined by standard methods.Results: Hemodynamics remained stable in all animals. During LAD occlusion platelet aggregability increased only in the regional coronary circulation (126% of baseline, p=.0001). At 40 minutes of reperfusion systemic platelet aggregability decreased (86% of baseline, p=.0001) and subsequently increased at 90 minutes of reperfusion in both the systemic (127% of baseline, p=.0001) and regional circulations (156% of baseline, p=.0001). Ischemia was evident by the absence of distal LAD flow during occlusion that returned during reperfusion and a typical response of myocardial stunning in each animal (stunning time=47.7 +5.2 minutes).Conclusions: This study demonstrates that platelet function is not static during ischemia-reperfusion. Instead, during ischemia regional platelet aggregability is increased. Systemic and regional platelet aggregability also increase during myocardial reperfusion. The mechanism of these responses is unknown but may be related to regional endothelial dysfunction created by ischemia. The response observed could also be explained by the release of proaggregatory mediators in the coronary and/or systemic circulation during ischemia-reperfusion. The relative hyeraggregability observed following reperfusion may be relevant for further investigations of coronary artery reocclusion occurring after the relief of myocardial ischemia.This work was supported by a grant from Medtronic Inc., Minneapolis, MN and the Department of Medicine, University of Maryland School of Medicine.     

Mitochondria: role in ischemia, reperfusion and cell death.

Recent advances in the knowledge of the biochemical basis of myocardial ischemia have enabled a better understanding of the complex sequence of events occurring in ischemic cardiomyopathy, whatever its manifestations. This has clearly highlighted the important role played by cardiac mitochondria in these events. At first only associated with energy production, mitochondria have been clearly shown to have other important functions, like the maintenance of calcium homeostasis, as well as ischemic and non-ischemic preconditioning, and also modulation of cellular life and death. The aims of this review are twofold: firstly, to review the current knowledge on mitochondrial morphology and structure, and how these can be affected by ischemia and ischemia-reperfusion; and secondly, to summarize the role of cardiac mitochondria in cardioprotection and modulation of cell death mechanisms.     

蝙蝠葛碱对兔心肌缺血再灌注时血清MDA浓度和SOD活性的影响

目的探讨蝙蝠葛碱（Dau）对兔心肌缺血再灌注（IR）时血清丙二醛（MDA）浓度和超氧化物歧化酶（SOD）活性的影响。方法24只家兔随机分为假手术对照组、缺血再灌注组、缺血再灌注＋蝙蝠葛碱（Dau）干预组各8例。结扎兔左冠状动脉前降支40min造成心肌缺血再灌注模型,观察缺血前后及再灌注不同时相点血清MDA含量和SOD活性的变化。结果家兔心肌缺血40min时血清MDA含量开始明显升高（P〈0．05）,SOD活性开始明显下降（P〈0．05）。Dau（剂量3．5mg／kg）能明显降低心肌缺血40min及缺血再灌注后兔血清MDA含量,升高血清SOD活性。结论Dau通过减轻兔心肌脂质过氧化作用所造成的损伤,增强SOD活性,提高氧自由基清除能力,对兔心肌缺血再灌注损伤具有一定保护作用。     

线粒体连接蛋白43参与缺血后处理对兔急性心肌缺血再灌注损伤的保护作用

目的 探讨线粒体连接蛋白43(connexin43,Cx43)和线粒体ATP敏感性钾通道(mitoK_(ATP)~+)在缺血后处理保护兔心肌缺血再灌注损伤中的作用.方法 新西兰大白兔64只,建立心肌缺血再灌注模型,给予冠状动脉左前降支30 min缺血,240 min再灌注.随机分为4组,每组16只:假手术组、缺血再灌注组、缺血后处理组和5-羟葵酸加缺血后处理组.测定血浆磷酸肌酸激酶同工酶(CK-MB),肌钙蛋白I(cTnI)含量以及心肌梗死面积,采用电子显微镜观测心肌线粒体结构变化,Western blot检测线粒体Cx43蛋白表达.结果 缺血后处理组心肌梗死面积为(19.1±3.9)%,明显低于缺血再灌注组(35.7±5.8)%,P＜0.01.再灌注4 h末血浆CK-MB与cTnI活性,缺血后处理组明显低于缺血再灌注组和5-羟葵酸加缺血后处理组(P＜0.01).与假手术组比较,其他各组线粒体均损伤明显(P均＜0.01);缺血后处理组线粒体损伤程度轻于缺血再灌注组(P＜0.01);缺血后处理组线粒体损伤程度明显轻于5-羟葵酸加缺血后处理组(P＜0.01).缺血再灌注组和5-羟葵酸加缺血后处理组线粒体Cx43蛋白表达均显著低于假手术组(P均＜0.05);缺血后处理组心肌线粒体Cx43蛋白表达明显高于缺血再灌注组(P＜0.05);缺血后处理组心肌线粒体Cx43蛋白表达明显高于5-羟葵酸加缺血后处理组(P＜0.05).结论 线粒体Cx43可能参与了缺血后处理的心肌保护作用,其机制可能与mitoK_(ATP)~+有关.     

神经型一氧化氮合酶在小鼠心肌缺血预处理中的作用

目的 应用神经型一氧化氮合酶(nNOS)基因敲除小鼠和nNOS抑制剂,探讨nNOS对心肌缺血预处理后心肌细胞凋亡的影响.方法 实验分为野生型缺血再灌注组(WT IR)、野生型缺血预处理组(WT IP)、野生型缺血预处理L-VNIO处理组(WT IP+ L-VNIO)、基因敲除鼠缺血再灌注组(KO IR)和基因敲除鼠缺血预处理组(KO IP).采用冠状动脉左前降支结扎法建立小鼠缺血再灌注损伤模型,缺血再灌注组缺血30 min再灌注3h,缺血预处理组分别经缺血5 min再灌注5 min连续三个循环后,再缺血30 min再灌注3h,观察TUNEL染色和Caspase-8、Caspase-9、Caspase-3的活性变化,并用Western Blot法观察Bax、Bcl-2和Fas蛋白的表达情况.结果 与WT IR组相比,WT IP组小鼠TUNEL阳性细胞数目减少,Caspase-8、Caspase-9和Caspase-3活性降低,Bax和Fas蛋白表达显著降低,Bcl-2表达显著增加(P＜0.05).而在KO IP组,与KO IR组相比,TUNEL阳性细胞数目和Caspase活性显著增加,Bax和Fas表达显著增高,Bcl-2表达显著降低(P＜0.05).结论 nNOS在心肌缺血预处理时发挥抑制心肌细胞凋亡的作用.     

Calpain system and its involvement in myocardial ischemia and reperfusion injury

Calpains are ubiquitous non-lysosomal Ca2+-dependent cysteine proteases also present in myocardial cytosol and mitochondria.Numerous experimental studies reveal an essential role of the calpain system in myocardial injury during ischemia,reperfusion and postischemic structural remodelling.The increasing Ca2+-content and Ca2+-overload in myocardial cytosol and mitochondria during ischemia and reperfusion causes an activation of calpains.Upon activation they are able to injure the contractile apparatus and impair the energy production by cleaving structural and functional proteins of myocytes and mitochondria.Besides their causal involvement in acute myocardial dysfunction they are also involved in structural remodelling after myocardial infarction by the generation and release of proapoptotic factors from mitochondria.Calpain inhibition can prevent or attenuate myocardial injury during ischemia,reperfusion,and in later stages of myocardial infarction.     

Impact of diabetes on induction of the mitochondrial permeability transition.

Diabetes is one of the most common metabolic diseases of our times. Specific cardiovascular alterations are often associated with the progression of this disease. Considerable controversy exists in the literature concerning the greater or lesser susceptibility of the diabetic heart to ischemia and reperfusion. Cardiac mitochondria may be fundamental to the differential susceptibility of the cardiomyocyte to pathologic phenomena, particularly those due to the induction of the degenerative process known as the mitochondrial permeability transition (MPT), which is triggered by excessive mitochondrial calcium accumulation. The MPT has been associated with cellular dysfunction resulting from ischemia and reperfusion. The objective of this work was to examine the susceptibility of mitochondria isolated from diabetic rats to the MPT, in comparison to healthy control rats of the same age. Cardiac mitochondria from the diabetic rats had higher calcium loading capacity before the development of the MPT, with a decreased incidence of MPTP-associated features. This was associated with a greater capacity to sustain multiple pulses of externally added calcium, simultaneously with maintenance of the transmembrane electrical potential and reduced swelling amplitude. This could mean that cardiomyocytes from diabetic hearts may indeed be less prone to dysfunctions resulting from ischemia and reperfusion, at least in milder diabetic conditions, thus explaining many reports in the literature.     

Prevention of transcoronary macromolecular leakage after ischemia-reperfusion by the calcium entry blocker nisoldipine. Direct observations in isolated rat hearts

Coronary microvascular damage appears to play a role in reperfusion injury after myocardial ischemia. This study was designed to afford direct viewing of the effects of myocardial ischemia-reperfusion on the coronary microcirculation and to determine whether pretreatment with the calcium blocker nisoldipine would attenuate any microvascular damage during reperfusion. Four groups of isolated rat hearts were perfused with a solution that contained red cells and fluorescent albumin, but was essentially free of platelets and leukocytes. Group I served as a nonischemic control. Group II hearts were subjected to 30 minutes of no-flow ischemia followed by reperfusion. Group III hearts were pretreated with nisoldipine (1 microgram/min) for 5 minutes before ischemia, and group IV hearts were treated with nitroglycerin (93 micrograms/min) before and after ischemia to mimic the vasodilation caused by nisoldipine. Perfused coronary capillarity and transcoronary extravasation of plasma albumin were measured by direct visualization techniques before and after ischemia. For group I, there was no significant change in coronary resistance, perfused capillarity, or transcoronary extravasation with time. For both groups II and IV, ischemia-reperfusion caused no increase in coronary resistance, but a significant decrease in perfused capillarity and a marked increase in transcoronary extravasation of fluorescent albumin (P less than 0.05). The nisoldipine group (group III) demonstrated a similar decrease in perfused capillarity but no increase in protein extravasation during reperfusion. These results indicate that, in the heart, platelets and/or leukocytes are not absolutely necessary to induce either the no-reflow phenomenon or the permeability damage observed during reperfusion after ischemia. The protective effect of treatment with nisoldipine appeared to be independent of vasodilation. We speculate that this calcium blocker reduced endothelial uptake of calcium during reperfusion, preventing endothelial deformation and formation of interendothelial gaps.     

Effects of calcium-channel blockers on myocardial preservation during experimental acute myocardial infarction

Calcium antagonists have become accepted agents for the attenuation of myocardial ischemia when it becomes manifest as angina pectoris. However, it is not known whether these agents can protect ischemic myocardium during the early evolution of an acute myocardial infarct. Calcium antagonists could potentially improve myocardial perfusion, by relieving coronary spasm or improving collateral blood flow, and reduce the energy demands of the ischemic myocardium either directly or by reducing heart rate or contractility. In some studies, calcium antagonists have decreased the rate of adenosine triphosphate depletion in ischemia and reduced functional or structural indexes of ischemic injury after relatively brief periods (up to 2 hours) of injury. We have assessed the ability of verapamil to protect severely ischemic myocardium in dogs with a 40-minute test period of circumflex occlusion followed by reperfusion. After 4 days of recovery, infarcts were sized by histologic methods. Untreated dogs had subendocardial infarcts (the more moderately ischemic subepicardial region being salvaged by reperfusion). Pretreatment with verapamil reduced the size of these subendocardial infarcts from 34 ± 8 to 8 ± 3 % of the ischemic circumflex vascular bed (anatomic area at risk). Thus, verapamil prevented cell death in a substantial proportion of the severely ischemic subendocardial region that otherwise would have died as a result of the 40-minute test period of ischemia. To establish whether verapamil could prevent cell death for a longer period of time in the less severely ischemic subepicardial region, a 3-hour period of coronary occlusion with reperfusion was studied. This period of occlusion caused infarcts averaging 60 ± 6 % of the ischemic area at risk in untreated dogs. Dogs treated with verapamil 15 minutes after occlusion and throughout the remaining 165 minutes of the 3-hour test period had no limitation of infarct size (53 ± 3 % of the area at risk). In untreated dogs, infarct size was related inversely to baseline subepicardial collateral flow. Verapamil neither improved collateral flow nor altered the regression of infarct size versus blood flow. Thus, the early protective effect of pretreatment with verapamil was not sustained when ischemia was prolonged to 3 hours and when verapamil was given 15 minutes after the onset of ischemia. In experimental studies from other laboratories, calcium antagonists have had either a protective effect or no effect when infarct size was evaluated after ≥3 hours of coronary occlusion. Preliminary results of clinical trials with calcium antagonists in acute myocardial infarction have not been encouraging. The available experimental data indicate that calcium antagonists can prevent ischemic cell death during relatively brief periods of ischemia if reperfusion is established, but it is uncertain whether these agents can limit infarct size when ischemia is maintained for longer periods.     

不同β受体阻滞剂对大鼠心肌间隙连接结构作用的对比研究

目的比较三代β受体阻滞剂的代表药物卡维地洛、美托洛尔及普萘洛尔对大鼠心肌缺血再灌注损伤心肌间隙连接（GJ）结构的不同作用。方法将大鼠随机分为假手术组、缺血再灌注组、卡维地洛组、美托洛尔组及普萘洛尔组。除假手术组只穿线不结扎外,其余各组均结扎左冠状动脉前降支30min,然后松开结扎线复灌4h,建立心肌缺血再灌注损伤模型。于再灌4h末用免疫荧光和激光扫描共聚焦显微镜技术观察心肌间隙连接蛋白43（CX43）的分布及组成变化,用激光扫描共聚焦显微镜对CX43进行定量。结果与假手术组相比,缺血再灌注组CX43-GJ结构明显异常。与缺血再灌注组比较,卡维地洛组、美托洛尔组和普萘洛尔组CX43-GJ损伤减轻。各药物治疗组间比较,卡维地洛组CX43-GJ结构损伤最轻。结论各种β受体阻滞剂均具有保护心肌GJ结构的作用,以卡维地洛的作用最明显。     

缺血后处理对心肌缺血再灌注的保护机制研究进展

缺血后处理(ischemic postconditioning)是在长时间缺血后再灌注早期,对心脏进行数次短暂的再灌注/缺血处理的方法。研究表明,缺血后处理与预处理一样能减轻再灌注心肌的损伤。其保护心肌的作用可能与抑制自由基生成、减轻钙超载、激活蛋白激酶、内源性生成物(如腺苷、阿片肽、一氧化氮等)激活、线粒体的ATP敏感性钾通道开放和线粒体通道转换孔关闭有关。现就后处理对心肌缺血再灌注的保护作用及其机制作一简要综述。