Synergistic Effects of Hydralazine and Alpha‐ or Beta‐Adrenergic Blockers: The Role of Plasma Renin Activity

Publisher Website
Google Scholar
Abstract
I.v. hydralazine, 0.15, 0.30 or 0.60 mg/kg, was administered to 11 supine hypertensives on 2 occasions, once after pretreatment with i.v. propranolol, 0.1 mg/kg, and once after pretreatment with i.v. placebo. The average fall in mean arterial pressure for each dosage of hydralazine was no different with or without propranolol, even though propranolol inhibited rises in plasma renin activity and pulse due to hydralazine. In each of 4 patients who had high supine baseline plasma renin activity, propranolol enhanced the fall in blood pressure caused by hydralazine. A 2nd group of patients was given an infusion of 0.01 or 0.02 mg/kg per min phentolamine, which did not change baseline blood pressure. Subsequent administration of i.v hydralazine, 0.15 mg/kg, resulted in a fall in blood pressure which was larger than previously observed with i.v. hydralazine alone, regardless of supine baseline plasma renin activity. The hypothesis is supported that reflex catecholamine release interferes with the hypotensive effect of i.v. hydralazine. Pretreating with propranolol weakens homeostatic defenses against hydralazine, such as rises in pulse rate and plasma renin activity. Propranolol appears to enhance the .alpha.-adrenergic effect of released catecholamines, and the antihypertensive response to hydralazine is unaltered. In patients with high supine plasma renin activity, propranolol potentiates the fall in blood pressure induced by hydralazine, perhaps because the hypertension in such patients is renin dependent.