Adenosine-enhanced ischemic preconditioning modulates necrosis and apoptosis: effects of stunning and ischemia-reperfusion

BACKGROUND: Adenosine-enhanced ischemic preconditioning extends the protection of ischemic preconditioning by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. METHODS: The effects of adenosine-enhanced ischemic preconditioning on necrosis and apoptosis were investigated in the sheep heart using models of stunning (15 minutes regional ischemia, 120 minutes reperfusion) and ischemia-reperfusion (30 and 60 minutes regional ischemia, 120 minutes reperfusion). Ischemic preconditioned hearts received 5 minutes regional ischemia, 5 minutes reperfusion before ischemia. Adenosine-enhanced ischemic preconditioned hearts received a 10 mmol/L adenosine bolus (10 mL) through the left atrium coincident with ischemic preconditioning. Adenosine hearts received a 10 mmol/L bolus (10 mL) of adenosine. Regional ischemic hearts received no pretreatment. RESULTS: Minimal apoptosis (< 45 per 3,000 myocytes) was observed in the stunning models but was significantly increased with ischemia-reperfusion in regional ischemic hearts after 30 minutes (p < 0.05 versus ischemic preconditioning, adenosine, or adenosine-enhanced ischemic preconditioning) and in adenosine and ischemic preconditioned hearts after 60 minutes ischemia (p < 0.05 versus adenosine-enhanced ischemic preconditioning). DNA laddering was apparent after 60 minutes ischemia in regional ischemia, adenosine, and ischemic preconditioning but not in adenosine-enhanced ischemic preconditioned hearts. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning significantly ameliorates necrosis and apoptosis in the regional ischemic blood-perfused heart.     

Protection against acute porcine lung ischemia/reperfusion injury by systemic preconditioning via hind limb ischemia

Previous work on various organs and tissues has shown that ischemic preconditioning protects against reperfusion injury in these organs and also against secondary effects in the lung. In contrast, the purpose of this study was to investigate the effects of preconditioning in a remote organ (hind limb ischemia) on an ischemia/reperfusion (I/R) treatment of the lung itself. A porcine model of in situ left lung ischemia (90 min) and reperfusion (5 h) was used. Systemic preconditioning was induced by clamping the left common femoral artery (3 x 5 min). Lung injury was assessed in terms of pulmonary vascular resistance, pulmonary artery pressure, pulmonary venous and arterial pO(2), and tissue macrophage counts. The zymosan-stimulated release of reactive oxygen species (ROS) in whole blood was determined by a chemiluminometric procedure. Inflammatory cytokines (interleukin-1beta and interleukin-6) were measured in arterial plasma as indicators of a systemic inflammatory reaction. Preconditioning by hind limb ischemia completely prevented the I/R-induced functional impairment of the lung, the pulmonary hypertension and the reduced oxygenation capacity. The plasma levels of interleukin-1beta and the macrophage counts in preconditioned animals were reduced to control values, whereas the levels of interleukin-6 and the release of ROS were not affected by preconditioning. In conclusion, systemic preconditioning by repeated hind limb ischemia protects against acute I/R injury of the lung but not against all indices of reperfusion-associated systemic inflammation.     

Ischemic preconditioning with opening of mitochondrial adenosine triphosphate-sensitive potassium channels or Na/H exchange inhibition: which is the best protective strategy for heart transplants?

OBJECTIVE: This study was designed to compare ischemic preconditioning with opening of mitochondrial adenosine triphosphate-sensitive potassium channels and Na(+)/H(+) exchange inhibition in an isolated heart model of cold storage, simulating the situation of cardiac allografts. METHODS: Sixty-seven isolated isovolumic buffer-perfused rat hearts were arrested with and stored in Celsior solution (Imtix-Sangstat) at 4 degrees C for 4 hours before a 2-hour reperfusion. Group I hearts served as controls and were arrested with and stored in Celsior solution. In group II, hearts were preconditioned by two 5-minute episodes of global ischemia, each separated by 5 minutes of reperfusion before arrest with Celsior solution. Group III hearts were arrested with and stored in Celsior solution supplemented with 100 micromol/L of the mitochondrial adenosine triphosphate-sensitive potassium channel opener diazoxide. In group IV, hearts received an infusion of diazoxide (30 micromol/L) during the first 15 minutes of reperfusion. Group V hearts underwent a protocol combining both interventions used in groups III and IV. In group VI, hearts were arrested with and stored in Celsior solution supplemented with 1 micromol/L of the Na(+)/H(+) exchange inhibitor cariporide. Group VII hearts received an infusion of cariporide (1 micromol/L) during the first 15 minutes of reperfusion. In group VIII, hearts underwent a protocol combining both interventions used in groups VI and VII. Group IX hearts were ischemically preconditioned as in group II, and sustained Na(+)/H(+) exchange inhibition during both storage and early reperfusion was used as in group VIII. RESULTS: On the basis of comparisons of postischemic left ventricular contractility and diastolic function, coronary flow, total creatine kinase leakage, and myocardial water content, values indicative of improved protection were obtained by combining ischemic preconditioning with Na(+)/H(+) exchange inhibition by cariporide given during storage and initial reperfusion. The endothelium-dependent vasodilatory postischemic responses to 5-hydroxytryptamine or acetylcholine and endothelium-independent responses to papaverine were not affected by these interventions. CONCLUSIONS: These data suggest that cardioprotection conferred by the Na(+)/H(+) exchange inhibitor cariporide is additive to that of ischemic preconditioning and might effectively contribute to improve donor heart preservation during cardiac transplantation.     

Pharmacological preconditioning with the adenosine triphosphate-sensitive potassium channel opener pinacidil

BACKGROUND: Ischemic preconditioning (IPC) decreases infarct size after global or regional ischemia. Potassium channel openers also precondition but are subject to dose-limiting vasodilation. We compared the mechanical and electrophysiological effects of ischemic and pharmacological preconditioning in an isolated rabbit heart model. METHODS: Rabbit hearts were preconditioned with either 10 micromol/L pinacidil alone (P-), 10 micromol/L pinacidil with 10 micromol/L phenylephrine (P+), or two cycles of global ischemia and reperfusion (IPC) before 1 hour of LAD occlusion. Left ventricular pressure, epicardial monophasic action potential duration (APD) and coronary flow were monitored throughout. Infarct size was determined at the end of reperfusion. RESULTS: Regional ischemia uniformly decreased APD (p<0.05). During reperfusion, APDs were prolonged beyond preischemic values in all preconditioned groups (p<0.05). P- and P+ reduced the incidence of fibrillation. P- significantly increased coronary flow (+15%, p = 0.001), whereas IPC and P+ did not. However, IPC and P- significantly decreased systolic function (p<0.05) but P+ did not. In addition, IPC depressed diastolic function (p<0.05) but P- and P+ did not. Infarct size was reduced by all methods (p<0.05). CONCLUSIONS: Pinacidil presents a safe and effective alternative to IPC for preserving the heart during regional ischemia. Its coronary vasodilatory effects are safely and effectively reversed by the addition of phenylephrine.     

Ischemic preconditioning in the aged heart —Myocardial protective effect as compared with the mature heart—

It is now well established that pre-treatment with sublethal ischemia, followed by reperfusion, will delay myocardial necrosis during a later sustained ischemic episode, termed ischemic preconditioning (IPC); this has been confirmed experimentally and clinically. However, the effects for the senescent heart differ from those of the mature heart at both functional and cellular levels which have not yet been determined. Comparisons were made between aged (>135 weeks, n=18) and mature (15～20 weeks, n=8) rabbit hearts which underwent 30 min. normothermic global ischemia with 120 min reperfusion in a buffer-perfused isolated, paced heart model, and the effects of IPC on post-ischemic functional recovery and infarct size were investigated. Ischemic preconditioned hearts (n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. Global ischemic hearts (n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n = 6) were subjected to perfusion without ischemia. Post-ischemic functional recovery was better in the ischemic preconditioned hearts than in the global ischemic hearts in both aged and mature hearts. However, in the aged hearts, post-ischemic functional recovery was slightly reduced compared to that of the mature hearts, and only the coronary flow was well-preserved. In the mature hearts, myocardial infarction in the ischemic preconditioned hearts (14.9 ± 1.3%) and in the control hearts (1.0 ± 0.3%) was significantly decreased (p<0.01) compared to that of the global ischemic hearts (32.9 ± 5.1%). In the aged hearts, myocardial infarction in the ischemic preconditioned hearts (18.9 ± 2.7%) and in the control hearts (1.1 ± 0.6%) was significantly decreased (p<0.001) compared to that of the global ischemic hearts (37.6 ± 3.7%). The relationship between infarct size and post-ischemic functional recovery of left ventricularpeak developed pressure (LVDP) was linear and the correlation negative, with r=?0.934 (p<0.001) and ?0.875 (p<0.001) for mature and aged hearts respectively. The data suggest that, in the senescent myocardium, the cellular pathways involved ischemic preconditioning responses that were post-ischemic, and that functional recovery was worse as compared to that of the mature myocardium. Furthermore, the effects of post-ischemic functional recovery became consistently weaker during the control period of 120 min. reperfusion after a prolonged ischemic insult in a buffer perfused isolated rabbit model. However, the effects of infarct size limitation were well-preserved in both senescent and mature myocardia.     

缺血预处理减轻骨骼肌缺血再灌注损伤

目的 观察缺血预处理对骨骼肌缺血再灌注损伤的保护作用。方法 选择２４只健康兔,随机等分为实验组和对照组。实验组先进行缺血预处理,再持续阻断后肢血流４ｈ;对照组直接阻断后肢血流４ｈ,制作骨骼肌缺血再灌注损伤模型。测定再灌注期血清中肌酸磷酸激酶（ＣＰＫ）和天门冬氨酸氨基转移酶（ＡＳＴ）,镜下观察骨骼肌变化。结果 实验组血清中ＣＰＫ和ＡＳＴ的含量均明显低于对照组（Ｐ〈０．０５）。实验组骨骼肌线粒体空泡变     

Amrinone preconditioning in the isolated perfused rabbit heart

BACKGROUND: Ischemic preconditioning (IPC) reduces infarct size in experimental preparations. IPC, however, is not without detrimental effects. We studied amrinone as a possible alternative to IPC. METHODS: Isolated perfused rabbit hearts were given a 5-minute infusion of 10 micromol/L amrinone followed by a 5-minute washout (n = 6). The anterior descending artery was then occluded for 1 hour and reperfused for 1 hour. Six hearts underwent IPC, with two episodes of 5-minute global ischemia followed by 5-minute reperfusion before LAD occlusion; eight control hearts received no preconditioning. Left ventricular pressure and ischemic zone epicardial monophasic action potentials were continuously monitored. RESULTS: IPC but not amrinone reduced peak pressure before anterior descending artery occlusion. Peak pressure fell significantly during ischemia and reperfusion in all hearts. End diastolic pressure rose significantly during reperfusion in control and IPC hearts but not in amrinone hearts. Action potentials shortened during ischemia in all hearts. They returned to preocclusion values in control hearts but lasted beyond preocclusion values in IPC and amrinone hearts. Both the incidences of ventricular fibrillation and infarct size were significantly reduced in amrinone hearts but not in IPC hearts. CONCLUSIONS: Amrinone is not only a useful inotropic agent but is also a superior preconditioning agent when compared to IPC.     

A noninvasive murine model of hind limb ischemia-reperfusion injury

BACKGROUND: This study describes a novel murine method of the Controlled Tension Tourniquet (CTT). The CTT applies a measured circumferential tension to hind limbs using a tourniquet attached to digital strain gauges, and is useful for investigating hind limb ischemia reperfusion (IR). MATERIALS AND METHODS: Mice were subjected to 1, 3, or 6 h of unilateral hind limb ischemia followed by either 4 or 24 h of reperfusion. Blood flow in the ischemic, reperfused, and contralateral limbs was monitored using a Laser Doppler Imager. Edema in the IR limbs was documented by changes in the wet weight to dry weight ratio. Myeloperoxidase and tetrazolium based mitochondrial activity assays indicated neutrophil infiltration and tissue viability, respectively. RESULTS: During reperfusion following 1, 4, or 6 h, flow stabilized at 100%, 53%, and 23% of baseline levels, respectively. Edema was present all in IR limbs after 4 h of reperfusion, but increased with the duration of ischemia. After 24 h of reperfusion neutrophil infiltration was equivalent in all IR limbs after all intervals of ischemia. After 24 h of reperfusion, tissue viability after 1 h of ischemia was equivalent to sham or contralateral limbs. At 3 or 6 h of ischemia and 24 h reperfusion decreased tissue viability to 40% of sham and contralateral limbs. CONCLUSIONS: The CTT provides a reproducible, noninvasive model of acute limb ischemia, which reflects the biochemical indices of microvascular injury, inflammation and flow characteristic of reperfusion injury.     

Myocardial protection by ischemic preconditioning and delta-opioid receptor activation in the isolated working rat heart.

OBJECTIVE: delta-Opioid receptors are involved in the cardioprotective effect of ischemic preconditioning. This study was designed (1) to assess the protective capacities of ischemic preconditioning and the synthetic delta-opioid receptor agonist D-Ala(2)-D-Leu(5) enkephalin (DADLE) in a functionally oriented experimental model of ischemia and reperfusion and (2) to assess whether the effects of both protective measures are similarly blocked by naloxone, a nonspecific delta-opioid receptor antagonist. METHODS: Sixty-four isolated working rat hearts were subjected to 45 minutes of hypothermic ischemia at 30 degrees C followed by 25 minutes of normothermic reperfusion. Rats were pretreated with DADLE (1 mg/kg body weight intravenously), naloxone (3 mg/kg body weight intravenously), or a combination thereof within 60 minutes before onset of isolated heart perfusion. During the preischemic perfusion period, 8 hearts per group were preconditioned by one cycle of 5 minutes of normothermic global ischemia and subsequent reperfusion whereas another 8 served as nonpreconditioned controls. The postischemic functional recovery of hearts and their creatine kinase leakage were determined. RESULTS: Pretreatment with DADLE and ischemic preconditioning improved the postischemic recovery of aortic flow when compared with nonpreconditioning (57.7% +/- 4.0% and 60.8% +/- 4.3% vs 40.0% +/- 4.2% of preischemic baseline value, P <.001). Combined pretreatment with DADLE before ischemic preconditioning afforded additional aortic flow recovery compared with pretreatment with DADLE alone (68.6% +/- 3.3% vs 57.7% +/- 4.0% of preischemic baseline value; P =.038). With combined pretreatment, early postischemic creatine kinase release was lower than control in hearts without pretreatment (0.48 +/- 0.11 vs 0.80 +/- 0.12 IU/5 minutes per heart; P =.001). Naloxone abolished the beneficial functional effects of pretreatment with DADLE and ischemic preconditioning. CONCLUSIONS: Pharmacologic activation of delta-opioid receptors affords improvement of functional protection in isolated working rat hearts similar to that conferred by classic ischemic preconditioning. The combination of both pretreatments reduces ischemic cellular damage and further adds to postischemic functional recovery. These changes are reversed by naloxone, an observation providing evidence that ischemic preconditioning involves signaling through opioid receptors.     

Preconditioning during warm blood cardioplegia

Objective: Preconditioning describes the cardioprotective effects of multiple brief episodes of warm ischemia. The purpose of the study was to determine whether warm ischemia, during the intermittent delivery of warm blood cardioplegia, would induce preconditioning during cardioplegia arrest. Methods: Dogs, 15, were randomized to a preconditioning protocol or to serve as controls. The control group received 60 min of continuous warm blood cardioplegia (WBC) followed by 30 min of warm arrested ischemia. The preconditioned group were arrested with WBC and then underwent three consecutive cycles consisting of 10 min of warm ischemia followed by 10 min of reperfusion. Reperfusion was provided by a continuous infusion of WBC. The preconditioning protocol was followed by 30 min of warm arrested ischemia. Myocardial functional recovery was assessed before cardiopulmonary bypass and cardioplegia arrest and again 30, 60 and 90 min after the arrest. Pressure-volume loops were used to measure the maximum elastance of the left ventricle (E_max), diastolic compliance, and used to calculate preload recruitable stroke work area. Results: Myocardial functional recovery was better preserved after 30 min of warm arrested ischemia in those animals that had been preconditioned. Conclusion: Preconditioning may be induced when warm blood cardioplegia is delivered intermittently during cardioplegia arrest.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

阿片受体在缺血预处理中的作用

目的　研究阿片受体激动在缺血预处理限制心肌梗死(心梗)范围作用中的地位。方法　建立在体家兔心脏缺血再灌注模型,观察阿片受体拮抗剂纳洛酮对缺血预处理心肌保护作用的影响。在离体兔心模型上,观察阿片受体激动剂吗啡代替短暂缺血刺激,对随后发生的急性心梗范围的影响,并用纳洛酮及蛋白激酶C阻断剂Chelerythrine分别进行干预。电镜观察吗啡预处理对离体心脏缺血心肌超微结构改变的影响。结果　在体心脏模型上,5min缺血及10min再灌注的预处理可显著缩小随后30min缺血引起的心梗范围(P＜0.01);在预处理前10min或30min、缺血前5min给予纳洛酮均可使预处理所产生的限制心梗范围的作用消失。离体心脏经历5min全心缺血及10min再灌注的预处理后,可缩小心梗范围(P＜0.05);在缺血前如给予吗啡预灌注15min,亦可缩小心梗范围(P＜0.05),其作用可被纳络酮或Chelerythrine分别阻断。30min缺血后心肌线粒体等超微结构严重受损,如给吗啡预灌流,心肌损伤明显减轻。结论　阿片受体激动参与了缺血预处理的心肌保护;吗啡预处理可以减轻缺血心肌损伤及产生限制心梗范围的心肌保护作用;吗啡是通过心脏局部的阿片受体介导,激活蛋白激酶C从而产生心肌保护作用。     

Ischemic preconditioning before lower limb ischemia--reperfusion protects against acute lung injury

OBJECTIVE: Prolonged limb ischemia followed by reperfusion (I/R) is associated with a systemic inflammatory response syndrome and remote acute lung injury. Ischemic preconditioning (IPC), achieved with repeated brief periods of I/R before the prolonged ischemic period, has been shown to protect skeletal muscle against ischemic injury. The aim of this study was to ascertain whether IPC of the limb before I/R injury also attenuates systemic inflammation and acute lung injury in a fully resuscitated porcine model of hind limb I/R. METHODS: This prospective, randomized, controlled, experimental animal study was performed in a university-based animal research facility with 18 male Landrace pigs that weighed from 30 to 35 kg. Anesthetized ventilated swine were randomized (n = 6 per group) to three groups: sham-operated control group, I/R group (2 hours of bilateral hind limb ischemia and 2.5 hours of reperfusion), and IPC group (three cycles of 5 minutes of ischemia/5 minutes of reperfusion immediately preceding I/R). Plasma was separated and stored at -70 degrees C for later determination of plasma tumor necrosis factor-alpha and interleukin-6 with bioassay as markers of systemic inflammation. Circulating phagocytic cell priming was assessed with a whole blood chemiluminescence assay. Lung tissue wet-to-dry weight ratio and myeloperoxidase concentration were markers of edema and neutrophil sequestration, respectively. The alveolar-arterial oxygen gradient and pulmonary artery pressure were indices of lung function. RESULTS: In a porcine model, bilateral hind limb (I/R) injury significantly increased plasma interleukin-6 concentrations, circulating phagocytic cell priming, and pulmonary leukosequestration, edema, and impaired gas exchange. Conversely, pigs treated with IPC before the onset of the ischemic period had significantly reduced interleukin-6 levels, circulating phagocytic cell priming, and experienced significantly less pulmonary edema, leukosequestration, and respiratory failure. CONCLUSION: Lower limb IPC protects against systemic inflammation and acute lung injury in lower limb I/R injury.     

吗啡预处理对缺血性心肌保护作用的研究进展

实验研究证实吗啡可以模拟缺血预处理.近年来吗啡预处理的心肌保护作用在在体、离体和心肌细胞3种动物模型都得到实验证实,其保护作用分为两个时相:即时相和延迟相.吗啡预处理的心肌保护作用主要由阿片受体介导,与线粒体KATP通道、诱导型NO合酶和环氧化酶等有关.将来在研究其分子机制的同时也会加强对其临床应用的研究.     

Preconditioning protects the severely atherosclerotic mouse heart

BACKGROUND: Coronary atherosclerosis has profound effects on vascular and myocardial biology, and it has been speculated that the atherosclerotic heart does not benefit from ischemic preconditioning. METHODS: To investigate if atherosclerosis would influence the preconditioning response, Apolipoprotein E/low density lipoprotein (LDL) receptor double knockout mice (ApoE/LDLr-/-) were fed an atherogenic diet (21% fat, 0.15% cholesterol) for 6 to 8 months. At that time, extensive atherosclerotic lesions throughout the coronary tree were seen in transverse sections stained with Oil Red-O. Hearts of ApoE/LDLr-/- mice were Langendorff-perfused with 40 minutes of global ischemia and 60 minutes reperfusion, and compared with C57BL/6 controls. Preconditioning with two episodes of 2 minutes of ischemia and 5 minutes reperfusion, or exposing the mice to a hyperoxic environment (O2 > 98%) for 60 minutes before heart perfusion, was performed. RESULTS: Hearts of mice with coronary atherosclerosis had worse postischemic function, and increased infarct size and troponin T release compared to hearts of C57BL/6 mice. Ischemic preconditioning improved postischemic ventricular function, and reduced myocardial infarct size and troponin T release in both normal and ApoE/LDLr-/- mice. The effects were most pronounced in ApoE/LDLr-/- hearts. Exposure to hyperoxia exerted a similar protection of function and cell viability of ApoE/LDLr-/- mice hearts. CONCLUSIONS: These findings suggest that the severely atherosclerotic heart may be protected by preconditioning induced by ischemia or hyperoxia.     

The effectiveness of ischemic preconditioning on myocardial protection and comparison with K(+) cardioplegia

The purpose of this study is to investigate the effects of ischemic preconditioning on myocardial protection and to compare this method to K(+) crystalloid cardioplegia. Langendorff perfused isolated working rat hearts were used in the following groups. After 20 min of stabilisation, 30 hearts were divided into three groups. In group I (control, n=10), hearts were arrested with cold (+4 degrees C) Krebs-Henseleit (K-H) solution, in group II (cardioplegia, n=10) hearts were arrested with cold K(+) cardioplegia solution, and in group III (preconditioning, n=10) hearts were subjected to 5 min normothermic ischemia followed by 5 min reperfusion then arrested with cold K-H solution. All hearts were subjected to 30 min of global ischemia (24 degrees C) and 40 min of reperfusion. Hemodynamic measurements were performed with a left ventricular latex balloon using a data acquisition system. Creatine kinase (CK-MB) washout and Troponin I (cTnI) levels were determined from the coronary effluents. There was no significant difference among the three groups in any of the parameters (hemodynamic and biochemical) measured at the end of stabilisation period. During reperfusion, functional recovery and coronary flow were significantly improved in K(+) cardioplegia and preconditioned groups compared with control group. CK-MB washout and cTnI levels were significantly lower in groups II and III compared with group I at the reperfusion. However no significant difference was observed between K(+) cardioplegia and preconditioned groups among biochemical and hemodynamic parameters and coronary flow at the post-ischemic period. In conclusion, ischemic preconditioning is as effective as K(+) cardioplegia on myocardial protection and recovery of myocardial function during reperfusion.     

In vivo chronic carvedilol treatment in rats attenuates ex vivo regional infarction of the heart

OBJECTIVE: Carvedilol is an alpha-and beta-blocking agent with antioxidant properties. We examined if treatment with carvedilol in vivo protected the heart against ischemic injury ex vivo. METHODS: Isolated hearts from treated rats (80 mg/kg/day) were subjected to 30 min regional ischemia. Hearts from non-treated animals received either no drug, 10 min carvedilol (1 microM) acute or ischemic preconditioning (IP) by 5 min ischemia +5 min reperfusion prior to regional ischemia. In separate experiments isolated hearts were subjected to 15 min global ischemia and 30 min reperfusion. RESULTS: Infarct size was significantly reduced by ischemic preconditioning or by chronic carvedilol treatment (9.0+/-0.9% and 7.2+/-1.9% of risk zone infarcted, respectively, vs. 33.8+/-6.4% in control hearts, mean+/-SEM, p < 0.05). Recovery of left ventricular developed pressure after global ischemia was not improved by carvedilol. Post-ischemic rise in left ventricular end diastolic pressure was, however, attenuated by chronic carvedilol treatment. CONCLUSION: Chronic in vivo but not acute ex vivo pretreatment with carvedilol significantly limited infarct size in isolated rat hearts.     

Cardioprotection afforded by ischemic preconditioning interferes with chronic beta-blocker treatment

OBJECTIVES: The efficacy of ischemic preconditioning of the heart has remained controversial. We investigated whether chronic treatment with beta-blockers affects the ischemic preconditioning in the isolated rat heart model. DESIGN: Wistar rats were treated with propranolol (50 mg/kg/day, p.o.) (PRL), with nipradilol (10 mg/kg/day, p.o.) (NPL), or with vehicle, for 4 weeks. Isolated rat hearts were divided into global ischemia hearts (GI, PRL and NPL, each n=6) and ischemic preconditioned hearts (IP, PRL+IP and NPL+IP, each n=6). RESULTS: Significant differences in left ventricular pressure were observed between the PRL and PRL+IP, and between the NPL and NPL+IP groups. In the NPL group, significant amelioration and preservation of left ventricular peak pressure, coronary flow, reduction of infarct size, and NOx preservation were observed. Lipid peroxidation in the NPL group was significantly reduced before and after global ischemia compared to the GI group. CONCLUSIONS: The effect of ischemic preconditioning was abolished in the hearts of rats following oral treatment of propranolol or nipradilol. However, the administration of nipradilol protected the ischemic and reperfused myocardium, partly due to the prevention of lipid peroxide formation.     

Effects of in vivo myocardial ischemia and reperfusion on interstitial nitric oxide metabolites

BACKGROUND: There have been numerous studies examining the role of nitric oxide (NO) in myocardial ischemia-reperfusion injury; however, few studies have included measurements of NO or related reactive nitrogen species. The purpose of this study was to determine the effects of in vivo regional myocardial ischemia on interstitial fluid (ISF) reactive nitrogen species. METHODS: Open chest pigs were submitted to one of three protocols: (1) 15 minutes coronary occlusion and 2 hours reperfusion, (2) 60 minutes coronary occlusion and 2 hours reperfusion, or (3) two-cycle ischemic preconditioning (IPC) followed by prolonged ischemia and 2 hours reperfusion. The stable NO metabolites, nitrite plus nitrate (NOx), in cardiac microdialysis samples were measured by ozone chemiluminescence. RESULTS: NOx concentration decreased 40% +/- 6% (p < 0.05) during brief ischemia but returned to baseline during reperfusion. Dialysate NOx levels decreased further after 60 minutes ischemia (60% +/- 3% of baseline, p < 0.01) but reperfusion dialysate NOx concentration increased 34% +/- 9% above baseline (p < 0.05). Preconditioning did not increase dialysate NOx but did accelerate the ischemia-induced decrease in NOx levels (p < 0.05). Reperfusion NOx levels in preconditioned pigs were significantly lower than in nonpreconditioned pigs (p < 0.05). CONCLUSIONS: These results suggest that ischemia is associated with decreased ISF NOx concentration. Reperfusion NOx levels are increased after prolonged ischemia, an effect that is significantly blunted by ischemic preconditioning.