Myocardial and endothelial dysfunction after multiple, brief coronary occlusions: role of oxygen radicals.

The major objective of the present study was to determine the effect of multiple, brief periods of coronary artery occlusion and reperfusion on postischemic contractile function (sonomicrometry) and endothelium-dependent vasodilator responses in isolated conduit coronary artery rings obtained from anesthetized dogs. The role of oxygen-derived free radicals was also investigated. Dogs were subjected to four 5-min episodes of left anterior descending coronary occlusion interspersed with 5 min of reperfusion followed by a final 60-min reperfusion period. The multiple occlusion-reperfusion protocol resulted in regional segment dysfunction (37 +/- 15% of preocclusion values at 60 min of reperfusion) and attenuated endothelium-dependent responses to acetylcholine, bradykinin, and the calcium ionophore, A23187. Responses to the endothelium-independent vasodilator, sodium nitroprusside, were unaffected. Infusion of superoxide dismutase (5,000 U/kg) and catalase (55,000 U/kg) markedly improved the recovery of myocardial function at 30 and 60 min of reperfusion and completely protected against vascular endothelial damage. These results suggest an important role for oxygen-derived free radicals in the myocardial and endothelial injury that occurs in this model of multiple stunned myocardium.