Acute hypotensive, natriuretic, and hormonal effects of nifedipine in salt-sensitive and salt-resistant black normotensive and hypertensive subjects

In a randomized double-blind study, we compared the short-term effects of n ifedipine (10 mg 3 x daily for 1 day) versus placebo on 24-h blood pressure , diuresis, natriuresis, urinary excretion of dopamine and metabolites, and on plasma renin activity (PRA) and plasma aldosterone levels in 18 black h ypertensive (HT) patients [eight salt-resistant (HT-SR) and 10 salt-sensiti ve (HT-SS)], and in 20 black normotensive (NT) subjects (12 NT-SR and eight NT-SS) who were studied randomly with both a high- (HS) and a low-salt (LS ) diet. In comparison to placebo, nifedipine significantly decreased 24-h m ean BP in all groups either with HS or LS diets (all p < 0.05). With HS, gr eater hypotensive effects were achieved in WT-SS (-10 +/- 2 mm Hg) versus N T-SR (-3 +/- 1 mm Hg; p < 0.05) and in WT-SS (-18 +/- 2 mm Hg) versus MT-SR (-12 +/- 2 mm Hg; p < 0.05). In NT-SS and HT-SS. nifedipine induced greate r (p < 0.05) BP decrease with HS (-10 +/- 2 and -18 +/- 2 mm Hg) than with LS (-3 +/- 1 and -9 +/- 1 mm Hg, respectively), whereas in NT-SR and MT-SR, the hypotensive effect did not differ between HS and LS. Nifedipine versus placebo significantly increased natriuresis and fractional excretion of so dium in all groups only with HS (p < 0.05) but not with LS diets. Only in H T-SS were the hypotensive and natriuretic effects of nifedipine significant ly correlated (r = -0.77; p < 0.01). Nifedipine produced a similar increase of the urinary excretion of dopamine, L-DOPA, and of DOPAC in all subjects , which did not correlate with hypotensive and natriuretic effects. Nifedip ine did not modify plasma levels of renin and of aldosterone except in NT-S S with HS, in whom nifedipine increased PRA levels (p < 0.05). We conclude that although nifedipine reduces BP in all groups of NT and HT with LS and I-IS diets, the effect is greater in salt-sensitive subjects with HS. Altho ugh in HT-SS with HS, the short-term natriuretic response to nifedipine may contribute to its hypotensive effects, the diuretic-natriuretic effect of nifedipine is not necessary for the expression of its hypotensive effect. M oreover, it is unlikely that any short-term effects of nifedipine either on the renal dopaminergic system or on the secretion of aldosterone explain n ifedipine short-term hypotensive and diuretic-natriuretic effects.