Characterization of propranolol-induced relaxation of coronary artery.

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Abstract
Effects of propranolol on coronary artery were investigated in isolated dog coronary arteries and in isolated hearts of rats and guinea pigs. Cumulative administration of dl-propranolol produced concentration-dependent relaxation of coronary arterial strips under K+-contracture. There was no difference in relaxant potency between the optical isomers of propranolol. Lidocaine produced less relaxation than dl-propranolol, while atenolol and practolol scarcely affected the contraction. dl-Propranolol-induced relaxation was significantly restored by additional Ca2+ or prevented by prior administration of Ca2+. In isolated hearts of rats and guinea pigs which were perfused at a constant coronary inflow and paced at a constant rate, bolus administration of dl-propranolol produced dose-dependent falls in coronary perfusion pressure without significant changes in myocardial contractile force. Propranolol may have relaxant activities on coronary arteries through inhibition of Ca2+ influx in the cell membrane of coronary arterial smooth muscle.