An evaluation of the coronary constriction following propranolol

This study attempts to determine whether a direct coronary vasoconstriction follows beta blockade with propranolol. Coronary blood flow was varied with the aid of a pump. When myocardial contractile force was plotted as a function of coronary blood flow a characteristic biphasic curve resulted. Autoperfusion without the pump resulted in a flow rate which fell on the knee of that curve. Any direct vasomotion therefore should shift that autoperfused flow rate off of that knee. When propranolol was given intravenously at 0.5 mg/kg a new contractile force--flow curve resulted but the autoperfused coronary blood flow remained at the knee of the curve. Since these data indicate that coronary flow fell precisely in proportion to myocardial metabolism it is concluded that all coronary vasoconstriction following propranolol is secondary to changes in metabolism.