Effects of nipradilol on myocardial ischaemia produced by coronary stenosis in dogs.

Effects of nipradilol which is a new beta-adrenoceptor blocking agent endowed with nitroglycerin-like vasodilator actions, its denitrated derivative (denitro nipradilol) and propranolol on abnormalities of regional myocardial shortening produced by partial occlusion of the left circumflex coronary artery (LCX) were studied in anaesthetized open-chest dogs. In the presence of LCX stenosis, nipradilol (0.1 mg kg-1, i.v.) produced marked decreases in heart rate and LVdP/dt without a significant increase in left ventricular end-diastolic pressure (LVEDP). It improved impaired myocardial segment shortening and restored normal cardiac lactate metabolism. Denitro nipradilol (0.2 mg kg-1 i.v.) and propranolol (0.2 mg kg-1 i.v.) both caused similar haemodynamic changes to nipradilol but also produced a significant increase in LVEDP. However, improvement by these two agents of regional dysfunction in the ischaemic myocardium was comparable to those seen with nipradilol. All three agents markedly inhibited isoprenaline-induced tachycardia, but vehicle did not. Atrial pacing abolished the beneficial effect of nipradilol on myocardial shortening in the ischaemic region without affecting other haemodynamic parameters. These results indicate that nipradilol alleviates acute myocardial ischaemia produced by coronary stenosis with similar efficacy to denitro nipradilol and propranolol suggesting, that a major part of the beneficial effect of nipradilol may be attributable to its beta-adrenoceptor blocking action.