ACUTE CARDIOVASCULAR ACTIVITY OF BETA-ADRENOCEPTOR BLOCKING-DRUGS IN AWAKE OR ANESTHETIZED NORMOTENSIVE AND HYPERTENSIVE RATS

Abstract

The effects of i.v. dl-propranolol (5 mg/kg), l- 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 anesthetized with urethane, chloralose or pentobarbital. Anesthesia may induce hemodynamic changes in hypertensive rats; urethane decreased peripheral vascular resistance in spontaneously hypertensive rats. In anesthetized rats, dl-propranolol, l- 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 anesthetized rats. l-Alprenolol had less cardiac effects than dl-propranolol. The decrease of blood pressure was shorter and/or smaller after d-alprenolol than after l-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. Differences in the initial vascular state, in the hypertensive models and in the anesthetics used can apparently explain the variability of the resposes to .beta.-adrenergic blocking drugs. .beta.-Blocking as well as quinidine-like activities are involved in the cardiovascular responses to dl-propranolol, d-alprenolol and l-alprenolol.