Effects of isradipine or enalapril on blood pressure in salt-sensitive hypertensives during low and high dietary salt intake

This large multicenter study, tested the antihypertensive effects of isradipine, a dihydropyridine calcium channel blocker and enalapril, an angiotensin-converting enzyme inhibitor, in salt-sensitive hypertensive patients under low and high salt intake diets. After a 3-week (weeks −9 to −6) of ad lib salt diet, those patients who had a sitting diastolic blood pressure (SDBP) of ≥95 but ≤115 mm Hg qualified to enter a 3-week (weeks −6 to −3) placebo run-in low salt diet (50 to 80 mmol Na+/day). Then high salt (200 to 250 mmol Na+/day) was added to the placebo treatment for 3 weeks (weeks −3 to 0). Those patients who demonstrated an increase in SDBP ≥5 mm Hg from the low to high salt diet were considered salt sensitive and were randomized into a 4-week (weeks 0 to 4) double-blind treatment period of either isradipine 2.5 to 10 mg twice a day, enalapril 2.5 to 20 mg twice a day, or placebo. Then they entered a 3-week (weeks 4 to 7) placebo washout phase of low salt diet (50 to 80 mmol Na+/day). After week 7 and while the low salt diet was continued the patients were restarted on their double-blind treatment for 4 more weeks (weeks 7 to 11) and the study was completed. Of 1916 patients screened, 464 were randomized into the double-blind treatment phase and 397 completed the study. Both isradipine and enalapril decreased the sitting systolic blood pressure (SSBP) and SDBP during the high salt diet, to a similar degree, whereas enalapril caused a greater reduction in SSBP and SDBP than isradipine during the low salt diet (11.3 ± 1.2/7.7 ± 0.7 mm Hg v 7.7 ± 0.9/4.8 ± 0.6 mm Hg, mean ± SEM, respectively, P< .02). Within drugs, the effect of isradipine on blood pressure (BP) was higher during the high than the low salt diet (14.9 ± 1.5 v 7.6 ± 1.3 mm Hg for SSBP and 10.1 ± 0.6 v 4.8 ± 0.9 mm Hg for SDBP, P< .001), but enalapril exerted a similar effect during both diets. Because salt restriction lowered both SSBP and SDBP, the lowest BP achieved with both drugs were during the salt restriction phase.