Phentolamine testing for alpha adrenergic participation in hypertensive patients: Independence from renin profiles

Abstract

To evaluate alpha adrenergic participation in sustaining blood pressure levels in hypertension. phentolanine. I mglmin for 20 min. was infUsed into 30 seated hypertensive patients. An average fall in diastolic blood pressure of 13.9 ± 9.2 (SD) mm Hg was induced: 21 of the 30 patients (70%) experienced a fall of at least 10%. Systolic blood pressure fell by 7.8 ± 15.7 mm H g. a decrement less (p < 0.05) than that for diastolic pressure. Heart rate increased by 36.2 ± 19.8 bpm and plasma renin activity increased by 1.5 ± 2.6 ng Iml Ihr during infusion. These increases did not correlate with the induced blood pressure changes and. thus. presumably reflected either the alpha blocking or perhaps beta agonistic properties of phentolamine. When patients were subdivided according to their renin‐sodium indices. there were no differences between the high. normal. and low renin subgroups in response to phentolamine and there was no correlation between control plasma renin activity and induced changes in systolic or diastolic blood pressure. Furthermore. in 24 patients who separately received an angiotensin‐converting enzyme inhibitor. teprotide. there was no relationship between the blood pressure decrements induced by it and those induced by phentolamine. In 13 patients in whom renin levels were stimulated by a restricted sodium diet. the blood pressure response to phentolamine was the same as that when they were studied on an unrestricted sodium diet. The results suggest that alpha adrenergic factors may often participate in sustaining blood pressure in hypertensive patients. This role is independent of the renin‐angiotensin system and of the state of sodium balance.