Ischemic preconditioning: triggering role of nitric oxide-derived oxidants in isolated hearts

There is evidence that oxidants generated during ischemic preconditioning (IPC) trigger or mediate cardioprotection. We examined whether a causal relationship exists between oxidant formation during ischemic preconditioning and cardioprotection. We monitored formation of dityrosine in crystalloid-perfused guinea pig isolated hearts after a preconditioning protocol and after prolonged ischemia. Superoxide dismutase, catalase, and glutathione (SCG), or the L-arginine analogue NGnitro L-arginine methyl ester (L-NAME) were given during preconditioning. Dityrosine was observed in the coronary effluent immediately after both stimuli, but not after bracketing with SCG or L-NAME. After prolonged ischemia, dityrosine was significantly lower in the IPC group than in other groups. IPC was evidenced by improved mechanical and metabolic function on reperfusion, and by reduced infarction. These effects were abrogated by either SCG or L-NAME. These data support the hypothesis that the formation of nitric oxide-derived oxidants during ischemic preconditioning is causally related to myocardial adaptation to reperfusion injury.     

Preservation of mitochondrial function during ischemia as a possible mechanism for cardioprotection of diltiazem against ischemia/reperfusion injury

A possible mechanism for D-cis-diltiazem (diltiazem)-mediated improvement of the contractile function of ischemic/reperfused hearts was examined. Thirty-five-min ischemia/60-min reperfusion recovered little the left ventricular developed pressure (LVDP) and decreased myocardial high-energy phosphates (HEPs). Ischemia induced an accumulation of tissue Na+ content, an increase in cytochrome c in the cytosolic fraction, and a decrease in the oxygen consumption rate (OCR) in perfused hearts. Treatment of the heart with 1 microM diltiazem for the last 3-min of pre-ischemia did not affect the decrease in HEPs during ischemia, whereas that with 3 microM partially attenuated the decrease in ATP, suggesting that 3 microM diltiazem exerted energy-sparing effect. Treatment with 1 microM diltiazem enhanced the post-ischemic recovery of LVDP associated with attenuation of the ischemia-induced accumulation of tissue Na+, increase in cytochrome c in the cytosolic fraction, and decrease in myocardial OCR, and restoration of the myocardial HEPs during reperfusion. Combined treatment with diltiazem and a Na+/H+ exchange inhibitor, but not a Na+ channel blocker, facilitated the attenuation of Na+ accumulation in the ischemic heart and the enhancement of the post-ischemic recovery of LVDP. Sodium lactate, a possible metabolite in ischemic hearts, and sodium chloride increased the Na+ concentration in mitochondria, released cytochrome c into incubation medium, and reduced the mitochondrial respiration. Treatment of isolated mitochondria with diltiazem failed to attenuate the sodium lactate- and sodium chloride-induced alterations. These results suggest that the cardioprotection of diltiazem may be exerted via attenuating cytosolic Na+ overload through Na+ channels in the ischemic heart, leading to preservation of mitochondrial functional ability during ischemia, followed by improvement of post-ischemic energy production and contractile recovery.     

Nicorandil preserves mitochondrial function during ischemia in perfused rat heart

A possible mechanism for the action of nicorandil on the improvement of energy metabolism of ischemic/reperfused hearts was examined. Perfused rat hearts were subjected to 35-min ischemia/60-min reperfusion. The heart was treated with nicorandil at concentrations of 10 to 100 microM for the last 30-min of pre-ischemia. Nicorandil preserved the mitochondrial oxygen consumption rate during ischemia and attenuated the decrease in mitochondrial function during reperfusion in association with the enhanced post-ischemic recovery of the left ventricular developed pressure. To assess the direct effect on mitochondria, myocardial saponin-skinned bundles were incubated under hypoxic conditions in vitro. Hypoxia-induced decrease in the mitochondrial oxygen consumption rate was attenuated by treatment of the bundles with 100 microM nicorandil. This attenuation was abolished by the combined treatment with the K(ATP) channel blocker, 5-hydroxydecanoate (5-HD). These results suggest that nicorandil is capable of attenuating ischemia/reperfusion injury of isolated perfused hearts through preservation of mitochondrial function during ischemia.     

Delayed cardioprotection by intestinal preconditioning is mediated by calcitonin gene-related peptide

Previous studies have shown that nitric oxide and calcitonin gene-related peptide (CGRP) are involved in mediation of the delayed cardioprotection of ischemic or pharmacological preconditioning, and nitric oxide can evoke the release of CGRP. In the present study, we examined the role of CGRP in nitric oxide-mediated delayed cardioprotection by brief intestinal ischemia in rats. The serum concentration of creatine kinase and infarct size were measured after 45-min coronary artery occlusion and 180-min reperfusion. Ischemic preconditioning was induced by six cycles of 4-min ischemia and 4-min reperfusion of the small intestine. Pretreatment with intestinal ischemic preconditioning for 24, 48, or 72 h significantly reduced infarct size and creatine kinase release, and the effects of ischemic preconditioning were completely abolished by L-nitroarginine methyl ester (L-NAME, 10 mg/kg, i.p.), an inhibitor of nitric oxide synthase, or by pretreatment with capsaicin (50 mg/kg, s.c.), which selectively depletes transmitters in capsaicin-sensitive sensory nerves. Intestinal preconditioning caused a significant increase in plasma concentrations of CGRP, and the effect was also abolished by L-NAME or capsaicin. These results suggest that the delayed cardioprotection afforded by intestinal ischemic preconditioning is mediated by endogenous CGRP via the nitric oxide pathway.     

The role of calcitonin gene-related peptide (CGRP) in ischemic preconditioning in isolated rat hearts

Brief coronary artery occlusion can protect the heart against damage during subsequent prolonged coronary artery occlusion; ischemic preconditioning. The role of calcitonin gene-related peptide (CGRP) in ischemic preconditioning is investigated in isolated perfused rat hearts, by measuring CGRP release during ischemic preconditioning and mimicking this by exogenous CGRP infusion, either in the absence or presence of the CGRP antagonist BIBN4096BS. CGRP increased left ventricular pressure and coronary flow in a concentration dependent manner, which was effectively antagonized by BIBN4096BS. Rat hearts (n=36) were subjected to 45 min coronary artery occlusion and 180 min reperfusion, which was preceded by: (1) sham pretreatment, (2) BIBN4096BS infusion (1 microM), (3) preconditioning by 15 min coronary artery occlusion and10 min reperfusion, (4) as 3, but with BIBN4096BS, (5) 15 min CGRP infusion (5 nM) and 10 min washout, (6) as 5, but with BIBN4096BS. Cardiac protection was assessed by reactive hyperaemia, creatine kinase release, infarct size related to the area at risk (%), and left ventricular pressure recovery. Preconditioning increased CGRP release into the coronary effluent from 88+/-13 to 154+/-32 pg/min/g, and significantly protected the hearts by decreasing reactive hyperaemia (35%), reducing creatine kinase release (53%), limiting infarct size (48%), and improving left ventricular pressure recovery (36%). Exogenous CGRP induced preconditioning-like cardioprotection. BIBN completely abolished the cardioprotection induced by preconditioning as well as by exogenous CGRP. In conclusion, since cardioprotection of preconditioning-induced CGRP release can be mimicked by exogenous CGRP, and both can be blocked by a CGRP antagonist, results indicate an important role for CGRP in ischemic preconditioning.     

降钙素基因相关肽在前列腺素介导豚鼠心脏缺血预适应中的作用(英文)

目的:研究降钙素基因相关肽与前列腺素在豚鼠心脏缺血预适应中的相互作用。方法:采用Langen-dorff方法灌注豚鼠离体心脏。记录心率、冠脉流量、左室内压以及最大变化速率,并测定冠脉流出液中降钙素基因相关肽(CGRP)与6-酮-PGF_(1α)的释放量。结果:内皮素-1(200 pmoL)引起心功能下降,表现为冠脉流量、心率、左室内压及其最大变化速率降低。缺血预适应可明显减轻内皮素-1引起的心脏损伤,同时预适应期间CGRP与6-酮-PGF_(1α)的释放量明显增加。应用辣椒素耗竭内源性CGRP后,缺血预适应的保护作用被取消。选择性CGRP_1受体拮抗剂CGRP_(8-37)100nmol/L也能取消缺血预适应的保护作用。环氧化酶抑制剂吲哚美辛(10μmol/L)可取消缺血预适应的保护作用,同时缺血预适应促进CGRP与6-酮-PGF_(1α)释放的作用也被取消。结论:前列腺素参与了缺血预适应对豚鼠心脏的保护作用,前列腺素的作用是由CGRP所介导。     

Effects of the angiotensin II subtype 1 receptor antagonist losartan on functional recovery of isolated rat hearts undergoing global myocardial ischemia-reperfusion

STUDY OBJECTIVE: To investigate the effects of the angiotensin II subtype 1 receptor (AT1R) antagonist losartan on functional recovery of isolated rat hearts undergoing global myocardial ischemia-reperfusion compared with myocardial protective effects of ischemic preconditioning. DESIGN: Ex vivo experiment using isolated perfused rat heart. SETTING: Academic laboratory. INTERVENTION: Hearts from Sprague-Dawley rats were perfused with oxygenated Krebs-Henseleit buffer and randomized to one of four groups: time control, vehicle, ischemic preconditioning, or losartan. MEASUREMENTS AND MAIN RESULTS: After randomization, hearts underwent 30 minutes of global ischemia followed by 30 minutes of reperfusion. Changes in end-diastolic pressure (EDP), left ventricular developed pressure (LVDP), and infarct size were examined between treatment groups by two-way analysis of variance with repeated measures. Cardiac angiotensin II receptor (ATR) density and infarct size were measured in control hearts and in a subgroup of hearts exposed to ischemia-reperfusion injury. Total ATR density and percentage of myocardial AT1R were increased in hearts exposed to ischemia-reperfusion. Myocardial ischemia-reperfusion injury resulted in a 56% reduction in LVDP from baseline in hearts randomized to vehicle. However, it declined by only 22% and 28% in hearts randomized to ischemic preconditioning and losartan, respectively. Compared with vehicle, both ischemic preconditioning and losartan decreased EDP (ischemic preconditioning 39 +/- 3 mm Hg, losartan 54 +/- 5 mm Hg, vs vehicle 78 +/- 8 mm Hg), and reduced infarct size (ischemic preconditioning 9%, losartan 12%, vs vehicle 36%). CONCLUSION: Treatment of isolated rat hearts with losartan before ischemia-reperfusion injury resulted in significant cardioprotection similar to that observed with ischemic preconditioning.     

Protection of calcitonin gene-related peptide-mediated preconditioning against lysophosphatidylcholine-induced myocardial injury in isolated rat hearts

研究心脏缺血预适应（ＰＣ）对溶血性磷脂酰胆碱（ＬＰＣ）损伤心肌作用的影响，并探讨降钙素基因相关肽（ＣＧＲＰ）在ＰＣ中的作用．离体大鼠心脏Ｌａｎｇｅｎｄｏｒｆ法灌流，记录心率，冠脉流量，左室压和左室压最大上升速率（＋ｄｐ／ｄｔｍａｘ），并测定灌流液中肌酸磷酸激酶（ＣＰＫ）含量．结果显示，ＬＰＣ能降低各项心功能指标，并使ＣＰＫ释放增加；ＰＣ（缺血５ｍｉｎ，再灌５ｍｉｎ，重复３次）能减轻ＬＰＣ的损伤作用；ＰＣ的心肌保护作用可被选择性ＣＧＲＰ受体拮抗剂ＣＧＲＰ８－３７所取消；预先给予ＣＧＲＰ或辣椒素能产生与ＰＣ相同的心肌保护作用．对照组，ＬＰＣ，ＰＣ＋ＬＰＣ，ＣＧＲＰ８－３７，ＣＧＲＰ８－３７＋ＰＣ＋ＬＰＣ，ＣＧＲＰ＋ＬＰＣ，ＣＧＲＰ８－３７＋ＣＧＲＰ＋ＬＰＣ，辣椒素＋ＬＰＣ组ＣＰＫ释放量分别为０．２６±０．０５，２．３０±０．２２，０．２５±０．０３，０．３０±０．０８，２．６０±０．１５，０．２４±０．０５，２．７０±０．２０和０．２５±０．０７μｍｏｌ·ｍｉｎ－１·ｇ－１湿组织．这些结果提示：１）ＰＣ对ＬＰＣ所致心肌损伤具有保护作用；２）ＰＣ的保护作用是由ＣＧＲＰ所介导；３）ＣＧＲＰ或辣椒素可模拟ＰＣ的保护作?     

Effect of sodium/hydrogen exchange inhibition on myocardial infarct size after coronary artery thrombosis and thrombolysis

This study examines the cardioprotective effects of Na+/H+ exchange inhibition with BIIB-722 or ischemic preconditioning after occlusive thrombus formation and subsequent thrombolysis for reperfusion. Coronary artery thrombosis was induced by vessel wall electrolytic injury. Thrombotic occlusion was maintained for 60 or 90 min in 4 different groups: (1) control; (2) Na+/H+ exchange inhibitor, BIIB-722 (3 mg/kg) before occlusion; (3) BIIB-722 (0.75 mg/kg) before reperfusion; (4) ischemic preconditioning (4 x 5 min). Thrombolysis with intracoronary recombinant tissue plasminogen activator produced reperfusion in 6.3 +/- 1.4 min (average for 68 dogs). After restoration of blood flow, vessel patency was maintained for 4 h with the glycoprotein IIb/IIIa receptor antagonist, BIBU 52ZW. BIIB-722, administered before (26.9 +/- 3.6%) or after (22.0 +/- 2.3%) 60-min ischemia or preconditioning (18.4 +/- 2.8%), produced comparable and significant reductions in infarct size (percent of area at risk) compared to controls (47.2 +/- 2.0%). After 90 min of ischemia, BIIB-722 administered before occlusion (37.3 +/- 1.1%) and ischemic preconditioning (35.0 +/- 4.8%) provided significant cardioprotection compared to control (45.9 +/- 1.8%). BIIB-722 was not cardioprotective when administered during occlusion (48.0 +/- 2.4%). The results indicate that Na+/H+ exchange inhibition and preconditioning provide a comparable degree of cardioprotection against 60 min of regional ischemia. However, when the regional ischemic period is extended to 90 min, the degree of cardioprotection is markedly reduced. Further studies incorporating clinically relevant events such as thrombosis and thrombolysis are required before one can conclude that Na+/H+ exchange inhibition is effective against more prolonged myocardial ischemia.     

缺血预适应的研究现状和前景

缺血预适应是一种内源性保护机理 ,即短暂缺血后能耐受随后较长时间的缺血损伤 ,这一现象已在不同种属动物和临床病人中得到证实 .缺血预适应表现为早期和延迟心肌保护 .缺血预适应的信号转导途径涉及触发物质 (内源性活性物质 ) ,中介物质 (蛋白激酶 )和效应物质 (离子通道和保护蛋白 ) .核因子 - κB可能在心肌缺血预适应的延迟保护中起重要作用 .缺血预适应已扩展到药理性预适应 ,单磷酯 A,尼可地尔等能显著减轻心肌缺血损伤 .     

Effect of calmodulin and protein kinase C inhibitors on globally ischemic rat hearts.

Several calmodulin inhibitors have been reported to be cardioprotective, but the ability of these compounds to inhibit protein kinase C (PKC) suggests that calmodulin inhibition may not be the sole mechanism responsible. To distinguish between the effects, we determined the cardioprotective activity of several calmodulin inhibitors with differing PKC inhibitory potencies in isolated globally ischemic rat hearts. Twenty-five minutes of global ischemia caused significant myocardial dysfunction, contracture formation, and lactate dehydrogenase (LDH) release on reperfusion in vehicle-treated hearts. The calmodulin inhibitors trifluoperazine, W-7, calmidazolium, W-13, and CGS 9343B improved postischemic contractile function and/or reduced LDH release. They also reduced preischemic cardiac function, although cardioprotection did not appear to be correlated with cardiodepression. Calmodulin inhibitors increased preischemic coronary flow (CF) and decreased heart rate (HR), but controlling these parameters did not affect the cardioprotection. Pretreatment of ischemic hearts with trifluoperazine was associated with preservation of myocardial ATP. Pretreatment of ischemic rat hearts with the PKC inhibitors staurosporine, calphostin C, polymyxin B, and H-7 did not result in cardioprotection. Thus, calmodulin inhibition causes cardioprotection that appears to be independent of PKC inhibition.     

An inhibitor of poly (ADP-ribose) synthetase activity reduces contractile dysfunction and preserves high energy phosphate levels during reperfusion of the ischaemic rat heart.

The cardioprotective properties of inhibition of poly (ADP-ribose) synthetase (PARS) were investigated in the isolated perfused heart of the rat. Hearts were perfused in the Langendorff mode and subjected to 23 min total global ischaemia and reperfused for 60 min. Left ventricular function was assessed by means of an intra-ventricular balloon. High energy phosphates were measured by 31P-NMR spectroscopy. Intracellular levels of NAD were measured by capillary electrophoresis of perchloric acid extracts of hearts at the end of reperfusion. Reperfusion in the presence of the PARS inhibitor 1,5 didroxyisoquinoline (ISO, 100 microM) attenuated the mechanical dysfunction observed following 1 h of reperfusion; 27+/-13 and 65+/-8% recovery of preischaemic rate pressure product for control and 100 microM ISO, respectively. This cardioprotection was accompanied by a preservation of intracellular high-energy phosphates during reperfusion; 38+/-2 vs 58+/-4% (P<0.05) of preischaemic levels of phosphocreatine (PCr) for control and 100 microM ISO respectively and 23+/-1 vs 31+/-3% (P < 0.05) of preischaemic levels of ATP for control and 100 microM ISO respectively. Cellular levels of NAD were higher in ISO treated hearts at the end of reperfusion; 2.56+/-0.45 vs 4.76+/-1.12 micromoles g(-1) dry weight (P<0.05) for control and ISO treated. These results demonstrate that the cardioprotection afforded by inhibition of PARS activity with ISO is accompanied by a preservation of high-energy phosphates and cellular NAD levels and suggest that the mechanism responsible for this cardioprotection may involve prevention of intracellular ATP depletion.     

内源性抗氧化酶在异氟烷预处理离体大鼠心肌保护作用中的变化

目的观察不同浓度异氟烷预处理离体大鼠心肌的保护作用及其与内源性抗氧化酶变化的关系。方法建立大鼠离体心脏Langendorff灌流模型,随机分为6组(n=14):空白对照组(CON组)、1.44MAC异氟烷对照组(ISO组)、缺血/再灌注组(I/R组)、0.72MAC(I1组)、1.08MAC(I2组)和1.44MAC(I3组)异氟烷处理组。除CON组和ISO组外,其余各组大鼠心脏均缺血30min,再灌注60min。异氟烷预处理在心脏缺血前25min时进行,用不同浓度异氟烷充分饱和的K-H液预处理20min,冲洗5min。记录平衡末,缺血前即刻,再灌注30、60min时的心功能指标,测定再灌注末心肌组织中内源性抗氧化酶的活性,计算心肌梗死面积。并检测I2组大鼠心肌在平衡末,缺血前即刻,缺血后即刻及再灌30min组织中内源性抗氧化酶的活力。结果心肌缺血/再灌注使离体大鼠心脏的LVEDP明显升高,HR、LVDP、dp/dtmin及dp/dtmax明显降低(P<0.05)。与I/R组比较,再灌注末,I2组和I3组LVEDP和心肌梗死面积均明显降低,HR、dp/dtmin、dp/dtmax以及各抗氧化酶活性明显升高(P<0.05)。与平衡末相比,在缺血后即刻心肌组织各内源性抗氧化酶的活性明显降低;而在再灌注30和60min时,其活性较缺血后即刻升高(P<0.05),但仍未达到平衡末水平。结论异氟烷预处理可以增强内源性抗氧化酶的活性,明显改善心功能,并减少心肌梗死面积,对大鼠离体缺血/再灌注心肌有保护作用。     

Effects of captopril on metabolic and hemodynamic alterations in global ischemia and reperfusion in the isolated working rat heart.

In the isolated working rat heart model, we studied metabolic and hemodynamic effects of 5- and 30-min global ischemia followed by reperfusion and assessed the potentially beneficial effect of captopril 80 micrograms/ml added throughout the experiment. Creatine kinase (CK) and catecholamines were measured in coronary effluent. De novo eicosanoids (prostaglandin E2) synthesis was assessed in endocardial explants. Hemodynamic alterations occurred after 30-min ischemia and were reflected most dramatically by a reduction in cardiac output (CO 72 +/- 10% of baseline values in captopril vs. 68 +/- 16% in controls) without significant differences as a result of treatment. Captopril shortened reperfusion ventricular fibrillation (VF) duration (6.9 +/- 1.2 vs. 13.6 +/- 8.7 min, p less than 0.05) but had no effect on VF incidence. No differences occurred in norepinephrine (NE) outflow, whereas total CK release was greater in controls. Five controls versus none of the treated hearts (p less than 0.05) released trace amounts of epinephrine during reperfusion. Increased de novo PGE2 synthesis was demonstrated after 5-min I (465 +/- 168 vs. 238 +/- 75 pg/100 mg tissue per hour, p less than 0.01). Captopril stimulated production of PGE2 in normoxic hearts (p less than 0.02), but the difference was no more apparent in ischemic hearts. We conclude that captopril produces some biochemical and electrophysiologic evidence of myocardial salvage, but these effects are not sufficient to induce hemodynamic improvement after global ischemia and reperfusion.     

Fenofibrate attenuates impaired ischemic preconditioning-mediated cardioprotection in the fructose-fed hypertriglyceridemic rat heart

We investigated in this study whether or not the ischemic preconditioning (IPC)-mediated cardioprotective effect against ischemia–reperfusion (I/R) injury exists in the fructose-fed hypertriglyceridemic (HTG) rat heart. Langendorff-perfused normal and fructose-fed (10 %?w/v in drinking water, 8 weeks) HTG rat hearts were subjected to 30-min global ischemia and 120-min reperfusion. IPC protocol included four brief episodes (5 min each) of ischemia and reperfusion. Myocardial infarct size using triphenyltetrazolium chloride staining, markers of cardiac injury such as lactate dehydrogenase (LDH) and creatine kinase (CK-MB) release, coronary flow rate (CFR), and myocardial oxidative stress were assessed. High degree of myocardial I/R injury, by means of significant myocardial infarct size, elevated coronary LDH and CK-MB release, reduced CFR, and high oxidative stress, was noted in the HTG rat heart as compared to the normal rat heart. The IPC-mediated cardioprotection against I/R injury was markedly impaired in the HTG rat heart as compared to the normal rat heart. Interestingly, pharmacological reduction of triglycerides using 8-week treatment protocol with fenofibrate (80 mg/kg/day, p.o.) restored the IPC effect in the HTG rat heart that was blunted by coinfusion, during the IPC reperfusion protocol, of a specific inhibitor of phosphoinositide-3-kinase (PI3-K), wortmannin (100 nM). The IPC failed to protect the HTG rat heart against I/R injury. Fenofibrate treatment reduced high triglycerides in the fructose-fed HTG rat and subsequently restored the cardioprotective effect of IPC.     

大蒜素通过激活蛋白激酶C模拟心肌缺血预适应(英文)

目的:研究大蒜素是否具有药物性预处理的作用,并探讨蛋白激酶C在大蒜素预处理中的重要作用。方法:34只离体家兔心脏挂上Langendorff装置,以95％O_2/5％CO_2混合的Krebs-Henseleit液灌流,均接受30min局部缺血和2h复灌。结果:在30min局部缺血前10min予5min药物性预处理的大蒜素组较之对照组明显缩小心肌梗塞范围(7％±6％ vs25％±7％,P<0.05),大蒜素 多粘菌素B组的心肌梗塞范围与对照组相比无显著性差异(23％±5％ vs 25％±7％,P>0.05)。结论:大蒜素具有模拟缺血预处理样保护作用,其作用可被抑制剂多粘菌素B所阻断,表明大蒜素通过激活蛋白激酶C发挥药物性预处理作用。     

Contribution of both the sarcolemmal K(ATP) and mitochondrial K(ATP) channels to infarct size limitation by K(ATP) channel openers: differences from preconditioning in the role of sarcolemmal K(ATP) channels

The roles of sarcolemmal ATP-sensitive K+ (sarcK(ATP)) and mitochondrial ATP-sensitive K+ (mitoK(ATP)) channels in the cardioprotection induced by K(ATP) channel openers remain unclear, though the mitoK(ATP) channel has been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning (PC). In the present study, selective inhibitors of the sarcK(ATP) and mitoK(ATP) channels were used to examine the role of each channel subtype in infarct size limitation by KATP channel openers. Isolated rabbit hearts were perfused in the Langendorff mode with monitoring of the activation recovery interval (ARI) and subjected to 30-min global ischemia/2-h reperfusion to induce infarction. Before ischemia, hearts received 10 microM pinacidil, 100 microM diazoxide, or PC with or without preceding infusion of a sarcK(ATP) channel-selective blocker (5 microM HMR1098) or a mitoK(ATP) channel-selective blocker (100 microM 5-hydroxydecanoate, 5-HD). ARI, an index of action potential duration, was shortened from 118+/-3 ms to 77+/-5 ms after 10 min of ischemia in untreated control hearts. Pinacidil shortened ARI before ischemia from 113+/-2 ms to 78+/-5 ms and enhanced the ARI shortening during ischemia. Diazoxide did not affect ARI before ischemia but accelerated ischemia-induced shortening of ARI. Infarct size as a percentage of the left ventricle (%IS/LV) was reduced by pinacidil and diazoxide from the control value of 47.2+/-4.0% to 4.5+/-1.5% and 5.2+/-1.2%, respectively. HMR1098 significantly inhibited the shortening of ARI by ischemia, pinacidil and diazoxide and partially blocked infarct size limitation by these K(ATP) channel openers (%IS/LV=32.6+/-4.2% and 23.4+/-5.3%, respectively). Infusion of 5-HD did not modify the change in ARI caused by the K(ATP) channel openers but completely abolished cardioprotection (%IS/LV=46.0+/-6.2% with pinacidil and 57.2+/-7.0% with diazoxide). PC with two episodes of 5-min ischemia limited %IS/LV to 21.6+/-4.0%, and this protection was not inhibited by HMR1098. Neither HMR1098 nor 5-HD alone modified infarct size. In conclusion, both sarcK(ATP) and mitoK(ATP) channels may contribute to the anti-infarct tolerance afforded by pinacidil and diazoxide.     

Possible role of cardiac mast cells in norepinephrine-induced myocardial preconditioning.

The present study was designed to investigate the role of cardiac mast cells in the cardioprotective effect of norepinephrine-induced preconditioning. Isolated rat heart was subjected to 30 min of global ischemia followed by 30 min of reperfusion. Both ischemic and norepinephrine (100 microM) preconditioning markedly reduced ischemia-reperfusion-induced release of lactate dehydrogenose (LDH) in the coronary effluent and the incidence of ventricular premature beats (VPBs) and ventricular tachycardia/fibrillation (VT/VF) during the reperfusion phase. Ischemic and norepinephrine preconditioning also significantly reduced ischemia-reperfusion-induced release of mast cell peroxidase (MPO), a marker of mast cell degranulation. However, MPO release increased immediately after ischemic or norepinephrine preconditioning. Histological study with ruthenium red (0.005%) staining confirmed cardiac mast cell degranulation in ischemic and norepinephrine preconditioned isolated rat hearts. These findings tentatively suggest that pharmacological preconditioning with norepinephrine produces a cardioprotective and antiarrhythmic effect similar to ischemic preconditioning through degranulation of resident cardiac mast cells.     

Possible involvement of erythropoietin in remote renal preconditioning-induced cardioprotection in rats

Remote preconditioning is a unique phenomenon in which brief episodes of ischemia and reperfusion to remote organs protect the target organ against sustained ischemia/reperfusion (I/R)-induced injury. Protective effects of remote renal preconditioning are well established in the heart, but their mechanisms still remain to be elucidated. Hence, the present study was designed to investigate the possible involvement of erythropoietin in remote renal preconditioning (RRPC)-induced cardioprotection in rats. RRPC was performed by 4 episodes of 5 min renal artery occlusion followed by 5 min reperfusion. Gentamicin (100 mg/kg intraperitoneal) was administered for 6 days for induction of renal failure. Isolated rat hearts were perfused on Langendorff apparatus and were subjected to global ischemia for 30 min ischemia followed by 120 min reperfusion. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) were measured in coronary effluent to assess the degree of myocardial injury. Extent of myocardial infarct size and coronary flow rate was also measured. RRPC prevented I/R-induced myocardial injury and produced cardioprotective effects. However, cardioprotective effects of RRPC were not observed in renal failure rats, indicating the protective role of humoral factor was released from functional kidneys. In renal failure rats, exogenous administration of rhEPO (5,000 IU/kg intraperitoneal) with RRPC restored the cardioprotective effects of later. These results implicate that RRPC-induced cardioprotective effects may be mediated through release of erythropoietin from kidney.     

Delayed preconditioning by cardiac ischemia involves endogenous calcitonin gene-related peptide via the nitric oxide pathway

Previous investigations have shown separately that calcitonin gene-related peptide (CGRP) or nitric oxide (NO) is involved in mediation of ischemic preconditioning. In the present study, we tested interactions of CGRP with NO in mediation of delayed preconditioning. In Sprague-Dawley rats, ischemia-reperfusion injury was induced by 45-min occlusion followed by 3-h reperfusion of coronary artery, and preconditioning was induced by four cycles of 3-min ischemia and 5-min reperfusion. Infarct size, plasma creatine kinase activity, the plasma level of NO and CGRP, and the expression of CGRP mRNA in dorsal root ganglion were measured. Pretreatment with preconditioning significantly reduced infarct size and the release of creatine kinase during reperfusion, and caused a significant increase in the expression of CGRP mRNA, concomitantly with an elevation in the plasma level of CGRP and NO. The effects of preconditioning were completely abolished by administration of L-nitroarginine methyl ester (L-NAME, 10 mg/kg, i.p.), an inhibitor of NO synthase. Pretreatment with capsaicin (50 mg/kg, s.c.), which depletes transmitters in capsaicin-sensitive sensory nerves, also blocked the cardioprotection of preconditioning and reduced the synthesis and release of CGRP, but did not affect the concentration of NO. The present results suggest the delayed protection afforded by ischemic preconditioning is also mediated by endogenous CGRP via the NO pathway in rat heart.