Impaired endothelium-dependent relaxation after coronary reperfusion injury: evidence for G-protein dysfunction

This study was done to determine whether abnormal receptor-dependent release of endothelium-derived relaxing factor (EDRF) might be caused by G-protein dysfunction. Dogs were exposed to global myocardial ischemia (45 minutes, induced by aortic cross-clamping) followed by reperfusion (60 minutes) while on cardiopulmonary bypass, and coronary arteries were then studied in vitro in organ chamber experiments. After reperfusion, endothelium-dependent relaxation to the receptor-dependent agonists adenosine diphosphate and acetyl-choline was significantly impaired as well as to sodium fluoride, which acts on a pertussis toxin-sensitive G-protein. In contrast, endothelium-dependent relaxations to the receptor-independent agonists A23187 and phospholipase C were normal. Furthermore, endothelium-dependent relaxation to poly-L-arginine (molecular weight, 139,200), which appears to induce endothelium-dependent relaxation of the canine coronary artery by a nonnitric oxide pathway, was unaffected by ischemia and reperfusion. These experiments suggest that global myocardial ischemia and reperfusion selectively impair receptor-mediated release of EDRF (nitric oxide) but that the ability of the endothelial cell to produce EDRF or generate endothelium-dependent relaxation to nonnitric oxide-dependent agonists remains intact. We hypothesize that coronary reperfusion injury leads to G-protein dysfunction in the endothelium.