Influence of Adrenergic Beta‐receptor Blockade on the Acute Cardiovascular Effects of Hydralazine*

Hydralazine lowers peripheral resistance and, therefore, the blood pressure, mainly by a direct action on vascular smooth muscle (Bein, Gross, Tripod & Meier, 1953; Ablad, 1963).In the human (Stein & Hecht, 1955; Ablad, 1963) and in the conscious dog (Grimson, 1952) the fall in blood pressure is accompanied by tachycardia.In anaesthetized dogs an increase in myocardial contractility has been found (Barrett, Povalski & Rutledge, 1965).Furthermore, in the dog, both the tachycardia (Brunner, Hedwall & Meier, 1965a) and the increase in myocardial contractility (Barrett et al., 1965) could be inhibited by adrenergic beta-receptor blockade.Thus it seemed possible that the action of hydralazine might involve direct stimulation of adrenergic beta- receptors.We therefore studied the influence of two adrenergic beta-receptor blocking agents, propranolol and CIBA 39,089-Ba [1-(o-allyloxyphenoxy)-3-isopropylamino-2propanol hydrochloride] (Brunner, Hedwall & Meier, to be published), on the acute cardiovascular effects of hydralazine in the dog and rat.