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 isradi pine, a dihydropyridine calcium channel blocker and enalapril, an angiotens in-converting enzyme inhibitor, in salt-sensitive hypertensive patients und er low and high salt intake diets. After a 3-week (weeks -9 to -6) of ad Ii b salt diet, those patients who had a sitting diastolic blood pressure (SDB P) of greater than or equal to 95 but less than or equal to 115 mm Hg quali fied 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 th e placebo treatment for 3 weeks (weeks -3 to 0). Those patients who demonst rated an increase in SDBP greater than or equal to5 mm Hg from the low to h igh salt diet were considered salt sensitive and were randomized into a 4-w eek (weeks 0 to 4) double-blind treatment period of either isradipine 2.5 t o 10 mg twice a day, enalapril 2.5 to 20 mg twice a day, or placebo. Then t hey 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 conti nued 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 screen ed, 464 were randomized into the double-blind treatment phase and 397 compl eted the study. Both isradipine and enalapril decreased the sitting systoli c blood pressure (SSBP) and SDBP during the high salt diet, to a similar de gree, whereas enalapril caused a greater reduction in SSBP and SDBP than is radipine during the low salt diet (11.3 +/- 1.2/7.7 +/- 0.7 mm Hg nu 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 hig h than the low salt diet (14.9 +/- 1.5 <nu> 7.6 +/- 1.3 mm Hg for SSBP and 10.1 +/- 0.6 nu 4.8 +/- 0.9 mm Hg for SDBP, P < .001), but enalapril exerte d 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. Am J Hypertens 2000;13:1180-1188 (C) 2000 American Jour nal of Hypertension, Ltd.