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 nifedipine (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 hypertensive (HT) patients [eight salt-resistant (HT-SR) and 10 salt-sensitive (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 mean BP in all groups either with HS or LS diets (all p < 0.05). With HS, greater hypotensive effects were achieved in NT-SS (-10 ± 2 mm Hg) versus NT-SR (-3 ± 1 mm Hg; p < 0.05) and in HT-SS (-18 ± 2 mm Hg) versus HT-SR (-12 ± 2 mm Hg; p < 0.05). In NT-SS and HT-SS, nifedipine induced greater (p < 0.05) BP decrease with HS (-10 ± 2 and -18 ± 2 mm Hg) than with LS (-4 ± 1 and -9 ± 1 mm Hg, respectively), whereas in NT-SR and HT- SR, the hypotensive effect did not differ between HS and LS. Nifedipine versus placebo significantly increased natriuresis and fractional excretion of sodium in all groups only with HS (p < 0.05) but not with LS diets. Only in HT-SS were the hypotensive and natriuretic effects of nifedipine significantly 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. Nifedipine did not modify plasma levels of renin and of aldosterone except in NT-SS 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 HS diets, the effect is greater in salt-sensitive subjects with HS. Although 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. Moreover, it is unlikely that any short-term effects of nifedipine either on the renal dopaminergic system or on the secretion of aldosterone explain nifedipine short-term hypotensive and diuretic-natriuretic effects.