EFFECT OF ADMINISTERED POTASSIUM ON THE RENIN-ALDOSTERONE AXIS IN YOUNG BLACKS COMPARED WITH WHITES

Background We had observed previously that the aldosterone excretion r ate and plasma aldosterone concentration were lower for black children than they were for white children. We did not know whether this was s econdary to a lower intake of potassium or to suppression of the renin -angiotensin system in blacks. Objective To test the hypothesis that t he secretion of aldosterone in response to potassium would be differen t in blacks than in a control group of whites. Design Slack and white subjects were selected on the basis of their having aldosterone excret ion rates that were in the lowest quartile for the entire original coh ort. Since the blacks typically had lower aldosterone excretion rates than did the whites, the black participants were represented primarily by those with average rates of aldosterone production among blacks, w hereas the whites were represented by those with the lowest aldosteron e production rates among whites. The protocol consisted of a placebo-c ontrolled, randomized cross-over study design. Methods Twelve blacks a nd 12 whites, aged 14.1 +/- 1.6 (mean +/- SD) and 15.4 +/- 2.1 years, respectively, were allocated randomly to double-blind treatment either with placebo or with 40 mmol/day potassium chloride for 7 days and th en the alternate treatment. Measurements of the plasma renin activity (PRA), plasma aldosterone concentration, and urinary aldosterone excre tion were performed in an inpatient research unit at the end of the tr eatment. The blood pressure was monitored for 24 h. Results Treatment with potassium increased the plasma aldosterone concentration (P = 0.0 006) and the urinary excretion of aldosterone (P = 0.0002) significant ly both for blacks and for whites. There was no significant racial dif ference in the response to potassium. The PRA was overall 1.605-fold t ower in the blacks than it was in the whites (P = 0.0124). The lowest PRA levels, such as those in the blacks when they were supine, tended to be increased with the potassium treatment The blood pressure did no t change significantly with the potassium supplement for either racial group. Conclusions After we had supplemented the intake of potassium, aldosterone production increased in the blacks and in the control gro up of whites to the same extent. The potassium treatment appeared to i ncrease lower PRA levels. A lower intake of potassium could at least p artially account for the suppression of the renin-aldosterone system i n blacks.