Nipradilol, a beta-adrenoceptor antagonist having a vasodilatory action, attenuates myocardial acidosis induced by coronary artery occlusion in dogs.

In dogs anesthetized with pentobarbital, the anterior descending coronary artery (LAD) was partially occluded to reduce LAD flow to about half of the original flow (partial occlusion). Myocardial pH (MpH) was measured by the use of a micro glass pH electrode. MpH decreased from 7.5-7.63 to 6.82-6.86 30 min after partial occlusion of the LAD. Nipradilol (0.3 mg/kg) was injected intravenously 30 min after partial occlusion, which continued for a further 60 min after nipradilol injection. Nipradilol decreased blood pressure and heart rate, and significantly increased myocardial pH which had been decreased by partial occlusion, within 60 min after injection. Nipradilol-induced restoration of the myocardial [H+] (calculated from the pH data), that had been increased by partial occlusion, was 48.5%. Bradycardia induced by nipradilol was not a determinant factor in the pH effect of nipradilol, because even in the paced heart, nipradilol restored the myocardial [H+] that had been increased by partial occlusion. These results indicate that nipradilol attenuates ischemia-induced myocardial acidosis, suggesting the favorable effect of nipradilol on ischemic myocardium. The favorable effect of nipradilol may be due to the beta-adrenoceptor antagonistic effect rather than the vasodilating effect.