5-HT2 receptor blocker sarpogrelate prevents downregulation of antiapoptotic protein Bcl-2 and protects the heart against ischemia-reperfusion injury

Even though reperfusion is the treatment of choice in patients admitted with acute myocardial infarction, reperfusion itself has been demonstrated to activate various pathological factors especially following procedures of cardiac revascularization. 5-hydroxytryptamine (5HT) is one such factor activated during reperfusion and is known to trigger the post ischemic contractile dysfunction and pathological apoptosis. Here we demonstrate the potential effects of the 5-HT(2)A antagonist sarpogrelate in protecting the myocardium against reperfusion injury of heart. Male Wistar rats weighing between 220 and 240 g were subjected to 30 min left coronary artery (LCA) occlusion and 120 min reperfusion. Sarpogrelate (4 mg/kg) was infused intravenously for 30 min either before LCA occlusion or at reperfusion. Following reperfusion the samples were collected for infarction area, immunohistochemistry, western blotting and myocardial metabolite analysis. Sarpogrelate infusion before ischemia resulted in (a) significant recovery of post ischemic cardiac functions (LVDP, EDP), (b) significant reduction in the infarct size among the risk area after triphenyl tetrazolium chloride staining (p<0.001), (c) decreased tissue water content (p<0.05), (d) well preserved myocardial ATP (p<0.05), (e) reduction in Bcl-2 downregulation and caspase 3 activation and (g) less prevalence of apoptotic cells (3.1+/-0.4% to 15.2+/-0.6%, drug versus control). Treating the rats with sarpogrelate during reperfusion also showed similar results. This study thus demonstrates the protective effects of sarpogrelate and supports the role for 5-HT2A inhibition in preventing the reperfusion injury of the heart.     

Ischemia-reperfusion injury leads to distinct temporal cardiac remodeling in normal versus diabetic mice

Diabetes is associated with higher incidence of myocardial infarction (MI) and increased propensity for subsequent events post-MI. Here we conducted a temporal analysis of the influence of diabetes on cardiac dysfunction and remodeling after ischemia reperfusion (IR) injury in mice. Diabetes was induced using streptozotocin and IR performed by ligating the left anterior descending coronary artery for 30 min followed by reperfusion for up to 42 days. We first evaluated changes in cardiac function using echocardiography after 24 hours reperfusion and observed IR injury significantly decreased the systolic function, such as ejection fraction, fractional shortening and end systolic left ventricular volume (LVESV) in both control and diabetic mice. The longitudinal systolic and diastolic strain rate were altered after IR, but there were no significant differences between diabetic mice and controls. However, a reduced ability to metabolize glucose was observed in the diabetic animals as determined by PET-CT scanning using 2-deoxy-2-((18)F)fluoro-D-glucose. Interestingly, after 24 hours reperfusion diabetic mice showed a reduced infarct size and less apoptosis indicated by TUNEL analysis in heart sections. This may be explained by increased levels of autophagy detected in diabetic mice hearts. Similar increases in IR-induced macrophage infiltration detected by CD68 staining indicated no change in inflammation between control and diabetic mice. Over time, control mice subjected to IR developed mild left ventricular dilation whereas diabetic mice exhibited a decrease in both end diastolic left ventricular volume and LVESV with a decreased intraventricular space and thicker left ventricular wall, indicating concentric hypertrophy. This was associated with marked increases in fibrosis, indicted by Masson trichrome staining, of heart sections in diabetic IR group. In summary, we demonstrate that diabetes principally influences distinct IR-induced chronic changes in cardiac function and remodeling, while a smaller infarct size and elevated levels of autophagy with similar cardiac function are observed in acute phase.     

Hypercholesterolemic Myocardium Is Vulnerable to Ischemia-Reperfusion Injury and Refractory to Sevoflurane-Induced Protection

Recent studies have demonstrated that volatile anesthetic postconditioning confers myocardial protection against ischemia-reperfusion (IR) injury through activation of the reperfusion injury salvage kinase (RISK) pathway. As RISK has been shown to be impaired in hypercholesterolemia. Therefore, we investigate whether anesthetic-induced cardiac protection was maintained in hypercholesterolemic rats. In the present study, normocholesteolemic or hypercholesterolemic rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Animals received 2.4% sevoflurane for 5 min or 3 cycles of 10-s ischemia/10-s reperfusion. The hemodynamic parameters, including left ventricular developed pressure, left ventricular end-diastolic pressure and heart rate, were continuously monitored. The infarct size, apoptosis, p-Akt, p-ERK1/2, p-GSK3β were determined. We found that both sevoflurane and ischemic postconditioning significantly improved heart pump function, reduced infarct size and increased the phosphorylation of Akt, ERK1/2 and their downstream target of GSK3β in the healthy rats. In the hypercholesterolemic rats, neither sevoflurane nor ischemic postconditioning improved left ventricular hemodynamics, reduced infarct size and increased the phosphorylated Akt, ERK1/2 and GSK3β. In contrast, GSK inhibitor SB216763 conferred cardioprotection against IR injury in healthy and hypercholesterolemic hearts. In conclusions, hyperchoesterolemia abrogated sevoflurane-induced cardioprotection against IR injury by alteration of upstream signaling of GSK3β and acute GSK inhibition may provide a novel therapeutic strategy to protect hypercholesterolemic hearts against IR injury.     

一氧化氮和线粒体ATP敏感性钾通道介导血管紧张素转换酶抑制剂加强阈下预处理的作用

实验采用离体大鼠心脏Langendorff灌流模型,观察含巯基（卡托普利）和不含巯基（培哚普利拉）的两种血管紧张素转换酶抑制剂（angiotensin-converting enzyme inhibitors,ACEI）对抗心肌缺血的作用,并探讨一氧化氮（nitric oxide,NO）和线粒体ATP敏感性钾通道（mimchondrial ATP-sensitive potassium channel,mitoKATP channel）是否参与ACEI的心肌保护作用。结果表明：（1）给予大鼠心脏2min全心停灌和10min复灌作为闽下缺血预处理（subthreshold preconditioning,sPC）、卡托普利或培哚普利拉单独使用,均不能改善长时间缺血复灌（缺血30min＋复灌120min）引起的心肌损伤。（2）当两种ACEI分别和sPC联合使用时,与sPC组相比,缺血心脏在长时间缺血后的复灌期问左室舒张末压（left ventricular end-diastolic pressure,LVEDP）明显降低,左宦发展压（left ventricular developed pressure,LVDP）和冠脉流量明显增高,乳酸脱氢酶（lactate dehydrogenase,LDH）的释放量和心肌梗死面积明显低于sPC组。（3）利用NOS抑制剂L-NAME和mitoKATP通道的抑制剂5-HD灌流10min后,可明显抑制卡托普利／培哚普利拉和sPC联合使用引起的LVEDP降低,并使LVDP和冠脉流量降低,LDH的释放量和心肌梗死面积明显增高（P〈0．05）。（4）sPC、卡托普利或培哚普利拉单独使用,心脏NO的产生增加。ACEI和sPC联合使用,与三者单独使用相比NO的浓度亦明显增高（P〈0．05）。结果提示：含与不含巯基的ACEI与闽下缺血预处理联合使用均可使大鼠心脏功能明显改善,其心肌保护作用的机制可能通过NO途径,并和mitoKATP通道的激活有关。     

Ischemic preconditioning fails to confer additional protection against ischemia-reperfusion injury in the hypothyroid rat heart

There is accumulating evidence showing that ischemic preconditioning (PC) may lose its cardioprotective effect in the diseased states. The present study investigated whether PC can be effective in hypothyroidism, a clinical condition which is common and often accompanies cardiac diseases such as heart failure and myocardial infarction. Hypothyroidism was induced in rats by 3-week administration of 6n-propyl-2-thiouracil in water (0.05 %). Normal and hypothyroid hearts (HYPO) were perfused in Langendorff mode and subjected to 20 min of zero-flow global ischemia and 45 min of reperfusion. A preconditioning protocol (PC) was also applied prior to ischemia. HYPO hearts had significantly improved post-ischemic recovery of left ventricular developed pressure, end-diastolic pressure and reduced lactate dehydrogenase release. Furthermore, phospho-JNK and p38 MAPK levels after ischemia and reperfusion were 4.0 and 3.0 fold lower in HYPO as compared to normal hearts (P<0.05). A different response to PC was observed in normal than in HYPO hearts. PC improved the post-ischemic recovery of function and reduced the extent of injury in normal hearts but had no additional effect on the hypothyroid hearts. This response, in the preconditioned normal hearts, resulted in 2.5 and 1.8 fold smaller expression of the phospho-JNK and phospho-p38 MAPK levels at the end of reperfusion, as compared to non-PC hearts (P<0.05), while in HYPO hearts, no additional reduction in the phosphorylation of these kinases was observed after PC. Hypothyroid hearts appear to be tolerant to ischemia-reperfusion injury. This response may be, at least in part, due to the down-regulation of ischemia-reperfusion induced activation of JNKs and p38 MAPK kinases. PC is not associated with further reduction in the activation of these kinases in the hypothyroid hearts and fails to confer added protection in those hearts.     

黑木耳多糖对抗离体心脏缺血/再灌注损伤的研究

目的:探讨黑木耳多糖(AAP)对离体大鼠心脏缺血/再灌注(I/R)损伤的防护作用及其机制。方法:健康雄性SD大鼠灌胃黑木耳多糖(50,100,200mg/(kg.d))4周后,采用离体心脏Langendorff灌流方法,全心停灌30min,复灌120min建立I/R模型。测定左心室动力学指标和再灌注各时间点冠脉流出液中乳酸脱氢酶(LDH)含量;实验结束测定心肌组织甲月赞(formazan)、丙二醛(MDA)含量及超氧化物歧化酶(SOD)活性的变化。结果:与单纯I/R组相比,AAP预处理明显提高心肌细胞的formazan含量,降低再灌注期间冠脉流出液中LDH含量,明显增强左室发展压、左心室内压最大上升速率和心率与发展压乘积的恢复,缓解冠脉流量的减少;高剂量AAP改善I/R心肌功能的作用要好于丹参预处理(4ml/(kg.d),gastricperfusion)组。中剂量AAP(100mg/(kg.d))预处理4周后明显抑制I/R心肌MDA的增加和SOD活性的减弱(P0.01),其效果要好于丹参阳性对照组。结论:在大鼠离体心脏灌流模型上,黑木耳多糖预处理具有抗心脏I/R损伤的作用,这种保护作用可能与其增加心肌SOD活性,减少脂质过氧化损伤有关。     

Cardioprotection from ischemia-reperfusion injury due to Ras-GTPase inhibition is attenuated by glibenclamide in the globally ischemic heart

The present study was designed to see if acute local inhibition of Ras-GTPase before or after ischemia (during perfusion) would produce protection against ischemia and reperfusion (I/R)-induced cardiac dysfunction. The effect of glibenclamide, an inhibitor of cardiac mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels, on Ras-GTPase-mediated cardioprotection was also studied. A 40 min episode of global ischemia followed by a 30 min reperfusion in perfused rat hearts produced significantly impaired cardiac function, measured as left ventricular developed pressure (P(max)) and left ventricular end-diastolic pressure (LVEDP). Perfusion with Ras-GTPase inhibitor FPT III before I/R [FPT(pre)], significantly enhanced cardiac recovery in terms of left ventricular contractility. P(max) was significantly higher at the end of 30 min reperfusion in FPT(pre)-treated hearts compared to pre-conditioned hearts. However, the degree of improvement in left ventricular contractility was significantly less when FPT III was given only after ischemia during reperfusion [FPT(post)]. Combination treatment with FPT III and glibenclamide before I/R resulted in significant reduction of FPT III-mediated cardioprotection. These data suggest that activation of Ras-GTPase signaling pathways during ischemia are critical in the development of left ventricular dysfunction and that opening of mitoK(ATP) channels, at least in part, contributes to cardioprotection produced by Ras-GTPase inhibition.     

Inhibition of ischemia/reperfusion-induced damage by dexamethasone in isolated working rat hearts: the role of cytochrome c release

We investigated the contribution of dexamethasone treatment on the recovery of postischemic cardiac function and the development of reperfusion-induced arrhythmias in ischemic/reperfused isolated rat hearts. Rats were treated with 2 mg/kg of intraperitoneal injection of dexamethasone, and 24 hours later, hearts were isolated according to the 'working' mode, perfused, and subjected to 30 min global ischemia followed by 120 min reperfusion. Cardiac function including heart rate, coronary flow, aortic flow, and left ventricular developed pressure were recorded. After 60 min and 120 min reperfusion, 2 mg/kg of dexamethasone significantly improved the postischemic recovery of aortic flow and left ventricular developed pressure from their control values of 10.7 +/- 0.3 ml/min and 10.5 +/- 0.3 kPa to 22.2 +/- 0.3 ml/min (p < 0.05) and 14.3 +/- 0.5 kPa (p < 0.05), 19.3 +/- 0.3 ml/min (p < 0.05) and 12.3 +/- 0.5 kPa (p < 0.05), respectively. Heart rate and coronary flow did not show a significant change in postischemic recovery after 60 or 120 min reperfusion. In rats treated with 0.5 mg/kg of actinomycin D injected i.v., one hour before the dexamethasone injection, suppressed the dexamethasone-induced cardiac protection. Electrocardiograms were monitored to determine the incidence of reperfusion-induced ventricular fibrillation. Dexamethasone pretreatment significantly reduces the occurrence of ventricular fibrillation. Cytochrome c release was also observed in the cytoplasm. The results suggest that the inhibition of cytochrome c release is involved in the dexamethasone-induced cardiac protection.     

Injection of isolated mitochondria during early reperfusion for cardioprotection

Previously, we demonstrated that ischemia induces mitochondrial damage and dysfunction that persist throughout reperfusion and impact negatively on postischemic functional recovery and cellular viability. We hypothesized that viable respiration-competent mitochondria, isolated from tissue unaffected by ischemia and then injected into the ischemic zone just before reperfusion, would enhance postischemic functional recovery and limit infarct size. New Zealand White rabbits (n = 52) were subjected to 30 min of equilibrium and 30 min of regional ischemia (RI) induced by snaring the left anterior descending coronary artery. At 29 min of RI, the RI zone was injected with vehicle (sham control and RI vehicle) or vehicle containing mitochondria (7.7 x 10(6) +/- 1.5 x 10(6)/ml) isolated from donor rabbit left ventricular tissue (RI-Mito). The snare was released at 30 min of RI, and the hearts were reperfused for 120 min. Our results show that left ventricular peak developed pressure and systolic shortening in RI-Mito hearts were significantly enhanced (P < 0.05 vs. RI-vehicle) to 75% and 83% of equilibrium value, respectively, at 120 min of reperfusion compared with 57% and 62%, respectively, in RI-vehicle hearts. Creatine kinase-MB, cardiac troponin I, and infarct size relative to area at risk were significantly decreased in RI-Mito compared with RI-vehicle hearts (P < 0.05). Confocal microscopy showed that injected mitochondria were present and viable after 120 min of reperfusion and were distributed from the epicardium to the subendocardium. These results demonstrate that viable respiration-competent mitochondria, isolated from tissue unaffected by ischemia and then injected into the ischemic zone just before reperfusion, significantly enhance postischemic functional recovery and cellular viability.     

Reduction of asymmetric dimethylarginine involved in the cardioprotective effect of losartan in spontaneously hypertensive rats

Previous studies have indicated that nitric oxide synthase (NOS) inhibitors can induce an increase of blood pressure and exacerbate myocardial injury induced by ischemia and reperfusion, whereas angiotensin II receptor antagonists protect the myocardium against injury induced by ischemia and reperfusion. Isolated hearts from male spontaneously hypertensive rats (SHR) or male Wistar-Kyoto rats (WKY) were subjected to 20 min global ischemia and 30 min reperfusion. Heart rate, coronary flow, left ventricular pressure, and its first derivatives (+/-dP/dt(max)) were recorded, and serum concentrations of asymmetric dimethylarginine (ADMA) and NO and the release of creatine kinase in coronary effluent were measured. The level of ADMA was significantly increased and the concentration of NO was decreased in SHR. Ischemia and reperfusion significantly inhibited the recovery of cardiac function and increased the release of creatine kinase, and ischemia and reperfusion-induced myocardial injury in SHR was aggravated compared with WKY. Vasodilation responses to acetylcholine of aortic rings were decreased in SHR. Treatment with losartan (30 mg/kg) for 14 days significantly lowered blood pressure, elevated the plasma level of NO, and decreased the plasma concentration of ADMA in SHR. Treatment with losartan significantly improved endothelium-dependent relaxation and cardiac function during ischemia and reperfusion in SHR. Exogenous ADMA also aggravated myocardial injury induced by ischemia and reperfusion in isolated perfused heart of WKY, as shown by increasing creatine kinase release and decreasing cardiac function. The present results suggest that the protective effect of losartan on myocardial injury induced by ischemia and reperfusion is related to the reduction of ADMA levels.     

11,12.环氧二十碳三烯酸预处理与后处理对缺血/再灌注大鼠心肌的保护作用

采用Langendorff离体灌流装置,通过停灌40 min/复灌30 min复制大鼠心肌缺血/再灌注(ischemia/reperfusion,IR)损伤模型,观察11,12-环氧二十碳三烯酸(11,12-epoxyeicosatrienoic acid,11,12-EET)预处理和后处理对心肌线粒体功能以及心功能的影响,探讨11,12-EET顸处理和后处理对IR大鼠心肌的作用及其机制.将30只Sprague-Dawley大鼠随机分为对照组、IR组、EET预处理组(Pre-EET)、EET后处理组(Post-EET),每组6只.除对照组外,其它各组全心缺血40 min,再灌注30 min.监测左心室内压差(ALVP)和左心室内压升降的最大变化率(±dp/dtmax)等心功能指标,测定灌流液中乳酸脱氢酶(1actate dehydrogenase,LDH)的活性.灌流结束后,测定心肌线粒体琥珀酸脱氢酶(succinate dehydrogenase,SDH)、Ca"ATPase、Na - K -ATPase活性以及心肌超氧化物歧化酶(superoxide dismutase,SOD)活性、丙二醛(malondialdehyde,MDA)含量.结果显示:(1)与IR组相比,Pre-EET组及Post.EET组Na -K -ATPase和SDH活性均增强,Ca2 -ATPase活性均减弱,有显著性差异(P<0.05);而Pre-EET与Post-EET组间没有显著性差异.(2)与IR组相比,Pre-EET组及Post-EET组心功能明显改善,LDH漏出显著减少,心肌SOD活性明显增强,MDA含量明显降低,有显著性差异(P<0.05);而Pre-EET与Post-EET组间没有显著性差异.结果表明,11,12-EET预处理及后处理均可通过上调心肌线粒体Na -K -ATPase、SDH活性以及下调Ca2 -ATPase活性改善线粒体功能和心肌能量代谢,拮抗心肌IR损伤;11,12-EET预处理及后处理还可通过提高心肌SOD活性、降低MDA含量改善IR心肌的氧化应激.     

Role of oxidative stress in alterations of mitochondrial function in ischemic-reperfused hearts

To study the mechanisms of mitochondrial dysfunction due to ischemia-reperfusion (I/R) injury, rat hearts were subjected to 20 or 30 min of global ischemia followed by 30 min of reperfusion. After recording both left ventricular developed pressure (LVDP) and end-diastolic pressure (LVEDP) to monitor the status of cardiac performance, mitochondria from these hearts were isolated to determine respiratory and oxidative phosphorylation activities. Although hearts subjected to 20 min of ischemia failed to generate LVDP and showed a marked increase in LVEDP, no changes in mitochondrial respiration and phosphorylation were observed. Reperfusion of 20-min ischemic hearts depressed mitochondrial function significantly but recovered LVDP completely and lowered the elevated LVEDP. On the other hand, depressed LVDP and elevated LVEDP in 30-min ischemic hearts were associated with depressions in both mitochondrial respiration and oxidative phosphorylation. Reperfusion of 30-min ischemic hearts elevated LVEDP, attenuated LVDP, and decreased mitochondrial state 3 and uncoupled respiration, respiratory control index, ADP-to-O ratio, as well as oxidative phosphorylation rate. Alterations of cardiac performance and mitochondrial function in I/R hearts were attenuated or prevented by pretreatment with oxyradical scavenging mixture (superoxide dismutase and catalase) or antioxidants [N-acetyl-L-cysteine or N-(2-mercaptopropionyl)-glycine]. Furthermore, alterations in cardiac performance and mitochondrial function due to I/R were simulated by an oxyradical-generating system (xanthine plus xanthine oxidase) and an oxidant (H(2)O(2)) either upon perfusing the heart or upon incubation with mitochondria. These results support the view that oxidative stress plays an important role in inducing changes in cardiac performance and mitochondrial function due to I/R.     

Enhanced death signaling in ozone-exposed ischemic-reperfused hearts

Although numerous advancements made in the field of human health have resulted in reduced deaths due to cardiovascular diseases (CVD), many patients with cardiac disease show no established risk. Therefore, other unknown factors may be responsible for the pathophysiology of CVD. Out of 350,000 sudden cardiac deaths each year in the United States, 60,000 deaths have been related to air pollution, suggesting a detrimental role of environmental pollutants in the development of CVD. The present study tested our hypothesis that chronic ozone exposure enhances the sensitivity to ischemia–reperfusion (I/R) injury in isolated perfused hearts. Sprague-Dawley rats were continuously exposed for 8 h/day for 28 and 56 days to filtered air or 0.8 ppm ozone. Isolated hearts were subjected to 30 min of global ischemia followed by 60 min of reperfusion. Cardiac function after I/R measured as left ventricular developed pressure (LVDP), +dP/dt, –dP/dt, and left ventricular end diastolic pressure (LVEDP) was significantly decreased and increased respectively in ozone-exposed I/R hearts compared to I/R hearts exposed to filtered air. The enhanced sensitivity to I/R injury upon ozone exposure was associated with increased myocardial TNF-α levels and lipid peroxidation and decreased myocardial activities of superoxidase dismutase (SOD) and IL-10. These data suggest that ozone-induced sensitivity to myocardial I/R injury may be due to promoting levels of oxidative stress as well as inflammatory mediators.     

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.     

Dexamethasone blocks sepsis-induced protection of the heart from ischemia reperfusion injury

Previous investigations have shown that sepsis, while causing cardiac dysfunction, can protect the heart from ischemia-reperfusion injury. Sepsis-induced protection may be due to nitric oxide produced by an inducible form of nitric oxide synthase generated in response to cytokines released during sepsis. The glucocorticoid dexamethasone has been shown to inhibit the synthesis of the inducible form of nitric oxide synthase (iNOS). The goals of this study were to determine if dexamethasone would prevent sepsis-induced cardiac dysfunction and sepsis-induced protection of the heart from ischemia-reperfusion injury. In this experiment, rats were made septic by injecting Escherichia coli into the dorsal subcutaneous space. Control rats were injected with sterile saline. At the time of surgery, some of the control and septic animals were injected intraperitoneally with dexamethasone (3 mg/kg). The next day, 24-26 hr after injection of the first dose of E. coli, animals were anesthetized, and hearts were removed and studied in the isovolumic beating-heart preparation. Left ventricular end diastolic pressure was set to 5 mmHg, and left ventricular pressure was measured continuously throughout the protocol. Left ventricular developed pressure (LVDP) was used as an index of LV function. After stabilization, hearts were made globally ischemic for 35 min and then reperfused for 25 min. As has been shown previously, sepsis depressed LVDP but also protected the heart from further depression of LVDP by ischemia and reperfusion. Dexamethasone prevented both sepsis-induced cardiac dysfunction and sepsis-induced protection of the heart from ischemia-reperfusion injury. In addition plasma nitrite/nitrate levels were not different from control levels in the dexamethasone-treated septic rats whereas levels were elevated in the septic animals. The dexamethasone mediated abrogation of sepsis-induced cardiac dysfunction and protection during ischemia-reperfusion injury may be due to suppression of nitric oxide production.     

The effects of sarpogrelate on cardiomyocyte hypertrophy

Sarpogrelate was developed as an antiplatelet agent antagonizing 5-hydroxytryptamine (5-HT) receptors. It had been reported that 5-HT receptors were expressed in cardiovascular system, and that sarpogrelate had antihypertrophic effects in vascular smooth muscle cells. Cardiac hypertrophy is a major problem in cardiac diseases, so the present study was designed to elucidate the effects of sarpogrelate on cardiac hypertrophy. Cultured rat cardiomyocytes (MCs) and cardiac nonmyocytes (NMCs) were prepared by Percoll gradient and adhesion method and MCs were incubated with (MCs/NMCs) or without NMCs. As an index of protein synthesis of MCs, [3H]-leucine uptake into MCs and MCs/NMCs was measured. Sarpogrelate decreased [3H]-leucine uptake into MCs (maximum 62.6+/-20.6% of control at 10(-4)M, p<0.05 vs. control). Sarpogrelate also significantly attenuated angiotensin-II- and endothelin-1-induced [3H]-leucine uptake. These results indicated that sarpogrelate might have antihypertrophic effects and could be a useful aid for cardiovascular disease.     

Ischemia-reperfusion injury changes the dynamics of Ca2+-contraction coupling due to inotropic drugs in isolated hearts.

Positive inotropic drugs may attenuate or exacerbate the deleterious effects of ischemia and reperfusion (IR) injury on excitation-contraction coupling in hearts. We 1) quantified the phase-space relationship between simultaneously measured myoplasmic Ca2+ concentration ([Ca2+]) and isovolumetric left ventricular pressure (LVP) using indexes of loop area, orientation, and position; and 2) quantified cooperativity by linearly modeling the phase-space relationship between [Ca2+] and rate of LVP development in intact hearts during administration of positive inotropic drugs before and after global IR injury. Unpaced, isolated guinea pig hearts were perfused at a constant pressure with Krebs-Ringer solution (37 degrees C, 1.25 mM CaCl2). [Ca2+] was measured ratiometrically by indo 1 fluorescence by using a fiber-optic probe placed at the left ventricular free wall. LVP was measured by using a saline-filled latex balloon and transducer. Drugs were infused for 2 min, 30 min before, and for 2 min, 30 min after 30-min global ischemia. IR injury worsened Ca2+-contraction coupling, as seen from decreased orientation and repositioning of the loop rightward and downward and reduced cooperativity of contraction and relaxation with or without drugs. Dobutamine (4 microM) worsened, whereas dopamine (8 microM) improved Ca2+-contraction coupling before and after IR injury. Dobutamine and dopamine improved cooperativity of contraction and relaxation after IR injury, whereas only dopamine increased cooperativity of relaxation before IR injury. Digoxin (1 microM) improved Ca2+-contraction coupling and cooperativity of contraction after but not before ischemia. Levosimendan (1 microM) did not alter Ca2+-contraction coupling or cooperativity, despite producing concomitant increases in contractility, relaxation, and Ca2+ flux before and after ischemia. Dynamic indexes based on LVP-[Ca2+] diagrams (area, shape, position) can be used to identify and measure alterations in Ca2+-contraction coupling during administration of positive inotropic drugs in isolated hearts before and after IR injury.     

Trolox C, a lipid-soluble membrane protective agent, attenuates myocardial injury from ischemia and reperfusion

The lipophilic antioxidant Trolox C, a vitamin E analog, was administered to isolated, buffer-perfused rabbit hearts subjected to 25 min of global stop-flow ischemia and 30 min of reperfusion. In six hearts, Trolox C (200 microM) was infused for 15 min immediately prior to ischemia and for the first 15 min of reperfusion. Six control hearts received only vehicle. Gas chromatography analysis confirmed that effective myocardial levels of Trolox were attained. At 30 min reperfusion, the recovery of left ventricular developed pressure was 56 +/- 3% of baseline in control hearts versus 70 +/- 4% in Trolox-treated hearts (p < .01). There was also significant improvement in recovery of Trolox-treated hearts in diastolic pressure and both maximum and minimum values of the first derivative of left ventricular pressure (dP/dt). Creatine phosphokinase release into the coronary effluent at 30 min of reperfusion was 16.5 +/- 8.4 IU/min in untreated and 6.3 +/- 1.0 IU/min (p < .05) in Trolox-treated hearts. Thus Trolox C, a lipophilic antioxidant, attenuated myocardial injury during stop-flow ischemia and reperfusion.     

TNF-alpha as a potential mediator of cardiac dysfunction due to intracellular Ca2+-overload

TNF-alpha has been shown to be involved in cardiac dysfunction during ischemia/reperfusion injury; however, no information regarding the status of TNF-alpha production in myocardial injury due to intracellular Ca2+-overload is available in the literature. The intracellular Ca2+-overload was induced in the isolated rat hearts subjected to 5 min Ca2+-depletion and 30 min Ca2+-repletion (Ca2+-paradox). The Ca2+-paradox hearts exhibited a dramatic depression in left ventricular developed pressure, a marked elevation in left ventricular end diastolic pressure, and more than a 4-fold increase in TNF-alpha content. The ratio of cytosolic to homogenate nuclear factor-kappaB (NFkappaB) was decreased whereas the ratio of phospho-NFkappaB to total NFkappaB was increased in the Ca2+-paradox hearts. All these changes due to Ca2+-paradox were significantly attenuated upon treating the hearts with 100 microM pentoxifylline. These results suggest that activation of NFkappaB and increased production of TNF-alpha may play an important role in cardiac injury due to intracellular Ca2+-overload.     

缺血后功能低下大鼠心肌钙与水含量的变化及高渗甘露醇的影响

缺血后心室功能减低(myocardial stunning)的发生机制迄今尚不明了。本实验以 Lang-cndorff 法在离体灌流的大鼠心脏,研究了全心缺血20min 及再灌注40min 后心肌 Ca~(2+)、Na~+K~+、Mg~(2+)及 H_2O 含量的变化,以及高渗甘露醇对缺血后功能低下心肌的影响。实验发现:(1)缺血/再灌注后心肌组织中 Ca~(2+),H_2O 的含量与非缺血组相比分别增加42%(P<0.01)及7.6%(P0.05)。(2)于再灌注同时给予12%高渗甘露醇可明显改善缺血后心室功能:再灌注40min 时,心率-左室压乘积恢复达缺血前的85%,而不给甘露醇仅恢复66.3%(p<0.01);高渗甘露醇同时消除了缺血后功能低下心肌中 Ca~(2+)超负荷与心肌水肿,此现象提示缺血/再灌注引起的肌膜非特异性通透性改变,很可能是钙进入细胞内的路径之一。本研究结果表明,心肌 Ca~(2+)超负荷及轻度心肌水肿参与了缺血后心室功能低下,高渗甘露醇在离体大鼠心脏可明显改善缺血后功能低下心肌的功能,此作用至少部分是由于其具有减低心肌钙与水含量的效应。