Significant role of alpha 2-adrenoceptors in coronary artery spasm

Ergonovine, 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 less than 0.001). Concomitant with the restoration of normal ST segment, plasma norepinephrine increased after the administration of yohimbine. Methoxamine and clonidine increased (p less than 0.01) and yohimbine decreased (p less than 0.01) coronary vascular resistance. Coronary spasm was visualized on coronary arteriogram after the application of clonidine; also coronary vasodilation was visualized after the administration of yohimbine. These results confirm the hypothesis that coronary artery spasm is mediated by pre- and postsynaptic alpha 2-adrenoceptors.