Adrenergic Receptor Activity in the Coronary Arteries of the Unanesthetized Dog

Both α- (vasoconstrictor) and β- (vasodilator) receptor activity was demonstrated in the coronary arteries of the unanesthetized dog independent of adrenergic receptors in the myocardium. In the β-receptor blocked animal, α-adrenergic receptor activity was demonstrated after intravenous and intracoronary injections of epinephrine and norepinephrine by the occurrence of coronary vasoconstriction which could be eliminated by blocking α-adrenergic receptors as well. Coronary vasoconstriction was also seen prior to β-receptor blockade after intravenous phenylephrine and, on occasion, after intracoronary injections of norepinephrine. β-adrenergic receptor activity was demonstrated in several instances after intravenous or intracoronary injections of catecholamines by an initial vasodilatation which could be eliminated by β-adrenergic receptor blockade and which occurred before there was any change in myocardial or systemic hemodynamics. The role of this independent adrenergic receptor activity in the control of the coronary circulation remains to be determined.