RESUMO
The haemodynamic effects of the two cardioselective B- adrenoceptor blockers, betaxolol and metoprolol were studied in experimental animals both in vivo and in vitro. In Vitro studies; Betaxolol had 8 times the potency of metoprolol in suppression of isoprenaline chronotropic activity and 5 times its potency in inhibition of myocardial contractility in isolated rabbit heart. In addiotn, betaxolol had less antagonistic effect than metoprolol to the isoprenaline effect on isolated guinea pig tracheal spiral strips. In vivo studies, betaxolol had 4 times the potency of metoprolol in oppression of isoprenaline induced tachycarida in anaesthetized 'dogs. Both betaxolol and metoprolol had no intrinsic sympathomimetic effect as they failed to increase heart rate in reserpinized rats. The IV injection of betaxolol in small doses O.I mg/kg 0.1 mg to 0.4 mg / kg induced rapid significant reduction in the arterial blood pressure of anaesthetized dog while metoprolol up to 0.8 mg/kg intravenously did not produce acute effect on the blood pressure. Chronic administration of the two beta adrenoceptor blockers in oral doses of 2.5 and 5mg/kg for 4 weeks were able to attenuate the rise in the blood pressure in the two kidney one-clip adult hypertensive rats. However, betaxolol effect was more pronounced and early occurred. In conclusion, the new beta adrenoceptor blocker betaxolol had more beneficial haemodnamic effect than metoprolol by which betaxolol is suggested to be a useful addition to the beta adrenoceptor blacker family