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The purpose of the present study was to investigate a possible role of opioid receptors in ischemic preconditioning (PC). To test this hypothesis, anesthetized, open-chest, male Wistar rats were subjected to five different protocols. In group I, the control group was subjected to 30 min of left coronary artery occlusion and 2 h of reperfusion. In group II, ischemic PC was elicited by three 5-min occlusion periods interspersed with 5 min of reperfusion. In group III, naloxone (NL, 3 mg/kg iv), a nonselective opioid antagonist, was given to nonpreconditioned rats 10 min before the 30-min occlusion period. Finally, NL was administered 10 min before preconditioning (NL + PC, group IV) or immediately after the last 5-min preconditioning period (PC + NL, group V). Infarct size (IS) as a percentage of the area at risk (AAR) (IS/AAR) was determined by 2,3,5-triphenyltetrazolium chloride staining. PC resulted in a marked reduction in myocardial IS from 45 +/- 5 to 8 +/- 1 (P < 0.05). NL treatment before or immediately after PC abolished this protective effect; however, NL had no effect on IS in non-PC rats. These results are the first to support the hypothesis that activation of opioid receptors may play an important role in ischemic PC in the rat myocardium.
Schultz et al. (1995) studied this question.