AIMTo investigate the effect of 8-opioid receptors in the cardioprotection elicited by ischemic postconditioning and the underlying mechanism.

METHODSThe isolated perfused hearts of male Sprague-Dawley rats were subjected to 30 min of global ischemia followed by 120 min of reperfusion. Formazan content of myocardium was measured spectrophotometrically, and the activity of lactate dehydrogenase (LDH) in the coronary effluent was measured. In isolated ventricular myocytes hypoxic postconditioning was achieved by 3 cycles of 5 min reoxygenation/5 min hypoxia starting at the beginning of reoxygenation, and cell viability was measured.

RESULTSIn the Langendorff perfused rat heart model, ischemic postconditioning (6 cycles of 10 s reperfusion/10 s global ischemia starting at the beginning of reperfusion) increased formazan content, reduced LDH release, improved the recovery of the left ventricular developed pressure, maximal rise/fall rate of left ventricular pressure and rate pressure product (left ventricular developed pressure multiplied by heart rate), attenuated the decrease of coronary flow during reperfusion and increased the isolated cell viability. Pretreatment with naltrindole, an antagonist of delta-opioid receptors and calcium-activated potassium channel (KCa) blocker paxilline attenuated the effect of ischemic/hypoxic postconditioning.

CONCLUSIONThe findings indicate that ischemic postconditioning protects myocardium against ischemia/reperfusion injury via activating delta-opioid receptors and opening KCa.