text: In anesthetized spontaneously hypertensive rats, the antihypertensive activity of carvedilol was nearly abolished by combined pretreatment of the rats with high doses of the alpha 1 adrenoceptor antagonist, prazosin (1 mg/kg, iv), and the nonselective << beta adrenoceptor >> antagonist, [[ propranolol ]] (3 mg/kg, iv), suggesting that the majority of the antihypertensive response produced by carvedilol may be accounted for by blockade of beta and alpha 1 adrenoceptors.