Effects of an Antihypertensive Agent, Nipradilol, on Isolated Coronary Artery of the Dog

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Abstract
Effects of nipradilol on proximal, middle and distal portions of left coronary arteries of the dog were investigated in vitro. Nipradilol (10–7–10–3M) produced a concentration-dependent relaxation in helical strips of isolated coronary artery under potassium contracture. The relaxation in the middle portions was most pronounced, it was 10% of the equimolar concentrations of nitroglycerin and significantly greater than that of propranolol. In the proximal portions of the coronary arteries, nipradilol (3 × 10–8–3 × 10–7M) showed a tendency to augment the contractile responses to norepinephrine; in the middle portions it reversed the relaxant responses to norepinephrine into contractile effects in a concentration-dependent manner. In distal portions, nipradilol significantly decreased the relaxant responses of the strips to norepinephrine. The findings demonstrate direct vasodilating and β-adrenoceptor blocking actions of nipradilol in isolated coronary arteries of the dog.