Characteristics of hypertension in the black population.

The renin-angiotensin system was examined in 146 black patients with essential hypertension. Classification into three categories was made according to plasma renin activity as measured by the radioimmunoassay of Angiotensin I and the accompanying sodium excretion. Differences among patients in the three renin groups (low, normal, and high) were not observed with respect to the incidence of cerebrovascular and cardiovascular events. No other discriminating variables could be identified by multivariate discriminant analysis. Low renin patients were distinguished in having a reduced sodium excretion compared to normal and high renin patients. Although total exchangeable sodium was not measured in this group of patients, other investigators have reported a higher exchangeable sodium in low renin patients than in those with normal or high values. This possibility, together with recent evidence in experimental models of low renin hypertension, that the affinity of angiotensin for its vascular receptors may be sodium dependent suggests that the incidence of vascular events may relate more specifically to angiotensin-vascular receptor interaction than to measurements of circulating renin.