Endothelium-dependent relaxation competes with alpha 1- and alpha 2-adrenergic constriction in the canine epicardial coronary microcirculation.

Abstract

These data confirm that alpha-adrenergic receptors are widespread in the coronary microcirculation, with the baseline functional responses to alpha 1-adrenergic activation predominating in small arteries and those to alpha 2-adrenergic activation predominating in arterioles. Furthermore, coronary microvascular constriction caused by both alpha 1- and alpha 2-adrenergic receptor activation is significantly modulated by endothelium-dependent relaxation, being markedly potentiated by inhibition of nitric oxide synthase activity. The data imply that alpha-adrenergic activation will assume considerable importance as a determinant of coronary microvascular resistance in pathophysiological situations associated with coronary endothelial impairment.