Why is plasma renin activity lower in populations of African origin?

Plasma renin activity is significantly lower in black people compared with whites independent of age and blood pressure status. The lower PRA appears to be due to a reduction in the rate of secretion of renin but the exact mechanistic events underlying such differences in renin release between blacks and whites are still not fully understood. Nevertheless, given the paramount importance of the renin-angiotensin system in the control of sodium balance, a most likely explanation is that the lower renin is a consequence of differences in renal sodium handling between blacks and whites. The lower PRA does not reflect differences in dietary sodium intake but the evidence available suggests that the low PRA could be part of the corrective mechanisms designed to maintain sodium balance in the presence of an increased tendency for sodium retention in black people. While it is possible that several factors may contribute to the reduced PRA, more recent investigation at the molecular level suggests that the lower PRA may arise from gene variation in the renal epithelial sodium channel. The functional significance of the lower PRA in relation to the different pattern of cardiovascular and renal disease between blacks and whites remains unclear. Moreover, direct investigations of pre-treatment renin status in hypertensive blacks in relation to blood pressure response have demonstrated that the pre-treatment PRA is not a good index of subsequent blood pressure response to pharmacological treatment. Nevertheless, the blood pressure reduction to short term sodium restriction is greater in blacks compared with whites and, in the black subjects, the greater reduction in blood pressure to sodium restriction appears to be related, at least in part, to the decreased responsiveness of the renin-angiotensin system.