Importance of the renin system for determining blood pressure fall with acute salt restriction in hypertensive and normotensive whites

Hypertensive (n=93) and normotensive (n=39) white individuals were given a high sodium intake of approximate to 350 mmol/d for 5 days followed by a lo w sodium intake of 10 to 20 mmol/d for 5 days. With this acute and large re duction in salt intake, no significant change was seen in blood pressure in the normotensive individuals, but blood pressure decreased in the hyperten sive individuals. Compared with normotensive subjects, hypertensive patient s had a 7/7-mm Hg greater fall in blood pressure (P<0.05 for systolic and P <0.01 for diastolic, adjusted for age), with similar changes in urinary sod ium excretion. From the high-salt to low-salt diet, plasma renin activity r ose from 0.90 to 5.99 ng . mL(-1) . h(-1) in normotensives, whereas in hype rtensives it rose from 0.73 to only 3.14 ng . mL(-1) . h(-1) (P<0.05 betwee n hypertensives and normotensives). Plasma aldosterone rose by 1396 pmol/L in normotensive subjects and by 511 pmol/L in hypertensive patients (P<0.05 ). Significant inverse correlations were obtained for all subjects between the fall in blood pressure from the high-salt to low-salt diet and the rise in plasma renin activity and aldosterone that occurred in addition to the absolute level on the low-salt diet. These results demonstrate that the lar ger fall in blood pressure with an acute reduction in salt intake in hypert ensives compared with normotensives is, at least in part, due to a less-res ponsive renin-angiotensin-aldosterone system in the hypertensive patients.