Acute cardiovascular activity of beta-adrenoceptor blocking drugs in awake or anaesthetized normotensive and hypertensive rats.

The effects of intravenous dl-propranolol (5 mg/kg), 1- and d-alprenolol (5 mg/kg), on blood pressure, heart rate, cardiac output and total peripheral resistance were investigated in normotensive and spontaneously, renal or neurogenic hypertensive rats. The animals were either awake or anaesthetized with urethane, chloralose or pentobarbital. Anaesthesia may induce hemodynamic changes in hypertensive rats; thus urethane decreased peripheral vascular resistance in spontaneously hypertensive rats. In anaesthetized rats, dl-propranolol, 1- and d-alprenolol caused significant falls in blood pressure, heart rate and cardiac output. The hypotensive activity was related to the initial blood pressure. Peripheral vascular resistance remained unchanged except in spontaneously hypertensive, chloralose anaesthetized rats. 1-Alprenolol had less cardiac effects than dl-propranolol. The decrease of blood pressure was shorter and/or smaller after d-alprenolol than after 1-alprenolol. In normotensive and renal hypertensive awake rats, dl-propranolol induced a short fall of blood pressure, due to a decrease of heart rate and cardiac output. These effects, except bradycardia, were not observed in spontaneously hypertensive rats. These results suggest that differences in the initial vascular state, in the hypertensive models and in the anaesthetics used can explain the variability of the responses to beta-adrenergic blocking drugs. Moreover, beta-blocking as well as quinidine-like activities are involved in the cardiovascular responses to dl-propranolol, d-alprenolol and 1-alprenolol studied here.