The renin-angiotensin system and blood pressure: differences between blacks and whites

Although blacks have lower plasma renin activity compared to whites, the corresponding differences in serum angiotensin converting enzyme (ACE) levels have not been well studied. Furthermore, few studies have examined the relationship of renin activity and ACE levels to blood pressure (BP) in blacks. We addressed these questions in a cross-sectional study conducted in 110 blacks and 183 whites who were not on antihypertensive medications. Three BP readings were obtained during a clinic visit. Plasma renin activity was assayed by radioimmunoassay and serum ACE levels were measured by spectrophotometry. Mean systolic and diastolic BP were 122.6 and 77.9 mm Hg in the blacks, and 123.4 and 77.9 mm Hg in the whites, respectively. Plasma renin activity was significantly lower in the blacks compared to the whites (0.92 v 1.26 ng/mL/h, respectively, P < .05), but ACE levels were similar in both groups (28.8 v 29.6 U/L, respectively). Renin activity was significantly and inversely associated with systolic and diastolic BP in both the blacks and the whites. ACE levels, however, were inversely associated with BP in the blacks but positively associated with BP in the whites (P = .02 for interaction on diastolic BP), even after adjustment for age, gender, body mass index (BMI), alcohol consumption, and heart rate. The corresponding interaction between ACE level and race on systolic BP was of borderline significance (P = .06). These results suggest that levels of ACE are similar in blacks and whites but their association with BP is possibly reflecting underlying ethnic differences in regulation of BP.