Age, blood pressure, renin and urinary electrolytes in primary hypertension and in the normotensive state

One hundred and twenty-three patients, sixty-four men and fifty-nine women, with primary hypertension were studied with regard to supine and sitting blood pressure (BP), plasma renin activity (PRA) during basal and stimulated conditions, and urinary sodium and potassium excretions. The patients ranged in age from 20 to 76 (mean 48) years. A control material of 120 normotensive subjects, forty-nine men and seventy-one women, with an age range 22-78 (mean 47) years were studied during the same strictly standardized conditions. The two populations were compared statistically. The mean basal PRA level, measured after 1 h supine rest, was significantly higher in the hypertensive subjects, while the upright PRA, determined after ambulation for 3-4 h, was the same in the two groups. On the contrary, the stimulated mean PRA, measured 3-4 h after intake of 80 mg frusemide orally was significantly lower in the hypertensive subjects. No relationships could be demonstrated between PRA and the 24 h urinary electrolyte excretions. An age dependent decrease of upright and stimulated PRA was demonstrated only in the hypertensive population. Applying our previously published reference ranges for stimulated PRA, 16 % of the hypertensive patients were considered to have low renin hypertension.