A pharmacological investigation on a possible calcium antagonistic action of propranolol

The present study was designed to investigate the mechanisms of smooth muscle relaxant effects of propranolol. The relaxant effects of the drug on potassium (K+)-contracture or lanthanum (La3+)-contracture were studied using smooth muscle preparations of dog coronary artery and colon in comparison with those of nitroglycerin, nifedipine and papaverine. Nitroglycerin relaxed the coronary artery preparations under K+-contracture as well as La3+-contracture, but did not relax the colon preparations under K+- and La3+-contracture. Papaverine relaxed both types of smooth muscles under K+- and La3+-contracture. Nifedipine relaxed the coronary artery and the colon preparations under K+-contracture, but did not relax them under La3+-contracture. Propranolol produced the same relaxant effects on both preparations as nifedipine. Furthermore, propranolol concentration-dependently inhibited the calcium-induced contractions of the coronary arterial preparations. The results suggest that propranolol, like nifedipine, may have a calcium antagonistic action in the cell membrane of smooth muscles.