RESUMO
Evidence indicates that ischemia/reperfusion (IR) results in endothelial dysfunction and neutrophil adhesion in the post-ischemic myocardium and that ischemic preconditioning (IPC), superoxide dismutase (SOD), and anti-endothelin-1 (ET-1) interventions prevent these effects. We tested the hypothesis that ET-1-induced superoxide (O(2)(-)) generation mediates endothelial injury and neutrophil accumulation in the IR heart, that IPC protects the endothelium and prevents the adhesion by attenuating post-ischemic ET-1, and thus O(2)(-), generation, and that the mitochondrial ATP-dependent potassium channel (mK(ATP)) triggers the IPC-induced protection. Langendorff-perfused guinea-pig hearts were subjected either to 30 min ischemia/35 min reperfusion (IR) or were preconditioned prior to IR with three cycles of either 5 min ischemia/5 min reperfusion or 5 min infusion/5 min wash-out of mK(ATP) opener diazoxide (0.5 microM). Neutrophils were infused to the hearts at 15-25 min of the reperfusion. Coronary flow responses to acetylcholine (ACh) and nitroprusside (SNP) served as measures of endothelium-dependent and -independent vascular function, respectively. Myocardial outflow of ET-1 and O(2)(-), P-selectin expression, neutrophil adhesion and functional recoveries were followed during reperfusion. IR augmented ET-1 and O(2)(-) outflow, P-selectin expression, and neutrophil adhesion, and impaired ACh response. These effects were attenuated or prevented by IPC and diazoxide, and 5-hydroxydecanoate (a selective mK(ATP) blocker) abolished the effects of IPC and diazoxide. SOD (150 U/ml) and tezosentan (5 nM, a mixed ET-1-receptor antagonist) mimicked the effects of IPC, although they had no effect on the ET-1 generation. The preventive effect of IPC, SOD and tezosentan on P-selectin expression preceded their effect on neutrophil adhesion. These data suggest that in guinea-pig heart: (i) ET-1-induced O(2)(-) generation mediates the post-ischemic endothelial dysfunction, P-selectin expression and neutrophil adhesion; (ii) IPC and diazoxide afford protection by attenuating the ET-1, and thus O(2)(-) generation; (iii) the mK(ATP) opening triggers the IPC protection; (iv) endothelial injury promotes post-ischemic neutrophil adhesion, but not vice versa.