Ischemic preconditioning prevents the impairment of hypoxic coronary vasodilatation caused by ischemia/reperfusion: role of adenosine A1/A3 and bradykinin B2 receptor activation.

We previously reported that hypoxic coronary vasodilatation (HCVD) is initiated by endothelial NO and sustained by adenosine. Prolonged ischemia/reperfusion impairs endothelium-dependent coronary vasodilatation, whereas transient ischemia (ie, preconditioning) protects the myocardium from subsequent ischemic events. Accordingly, we assessed whether prolonged ischemia/reperfusion impairs HCVD and whether preconditioning prevents this dysfunction. HCVD, elicited in isolated guinea pig hearts by a 1-minute exposure to 100% N2, consisted of an approximately 70% increase in coronary flow associated with enhanced nitrite/nitrate and adenosine overflow (+40% and 5-fold, respectively). After 30-minute global ischemia and 20-minute reperfusion, HCVD was decreased by approximately 60%, and the increases in nitrite/nitrate and adenosine overflow were abolished. Preconditioning (ie, three cycles of 5-minute global ischemia+5-minute reperfusion) prevented the impairment of HCVD and fully restored the increase in nitrite/nitrate overflow, but not that of adenosine. The protective effect of preconditioning was mimicked by perfusion with the adenosine A1 receptor agonist N6-cyclopentyladenosine and prevented by the A1 receptor antagonist N-0861. In addition, the A3 receptor agonist N6-(3-iodobenzyl)adenosine-5'-N-methyl-carboxamide had a similar protective effect. The bradykinin B2 receptor antagonist HOE 140 abolished the protective effect of preconditioning, whereas the NO synthase inhibitor N(omega)-methyl-L-arginine and the cycloxygenase inhibitor indomethacin did not. Our data indicate that preconditioning restores HCVD by a process that is triggered by activation of adenosine A1/A3 and bradykinin B2 receptors. The action of bradykinin is independent of NO and prostacyclin production. Once restored by preconditioning, HCVD is mediated by NO but no longer sustained by adenosine.