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 me chanistic events underlying such differences in renin release between black s and whites are still not fully understood. Nevertheless, given the paramo unt importance of the renin-angiotensin system in the control of sodium bal ance, 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 mechani sms designed to maintain sodium balance in the presence of an increased ten dency for sodium retention in black people. While it is possible that sever al factors may contribute to the reduced PRA, more recent investigation at the molecular level suggests that the lower PRA may arise from gene variati on in the renal epithelial sodium channel. The functional significance of t he lower PRA in relation to the different pattern of cardiovascular and ren al disease between blacks and whites remains unclear. Moreover, direct inve stigations 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 sub jects, the greater reduction in blood pressure to sodium restriction appear s to be related, at least in part, to the decreased responsiveness of the r enin-angiotensin system.