Significant Role of α₂-Adrenoceptors in Coronary Artery Spasm : SYMPOSIUM ON PATHOGENESIS OF CORONARY ARTERY SPASM

Abstract

Ergnovine, methoxamine and clonidine were administered intravenously in order to clarify the mechanism of coronary artery spasm in canine experiments. After these administrations, 27.5% of the dogs treated with ergonovine, 59.5% of the dogs treated with methoxamine and 72.7% of the dogs treated with clonidine showed ST segment elevation. The combined application of propranolol with ergonovine or methoxamine could more easily induce ST segment elevation than a single application of ergonovine or methoxamine. Most cases of elevated ST segment returned to the normal after the administration of nitroglycerin and phentolamine. Yohimbine was completely effective for the restoration of normal ST segment. Plasma norepinephrine decreased to 20±8.0% of the control when ST segment elevation was induced. This is a significantly greater decrease than that seen without ST segment elevation (p<0.001). Concomitant with the restoration of normal ST segment, plasma norepinephrine increased after the administration of yohimbine. Methoxamine and clonidine increased (p<0.01) and yohimbine decreased (p<0.01) and yohimbine decreased (p<0.01) coronary vascular resistance. Coronary spasm was visualized on coronary arteriogram after the application of clonidine; also coronary vascodilation was visualized after the administration of yohimbine. These results confirm the hypothesis that coronary artery spasm is mediated by pre- and postsynapic ₂-adrenoceptors.