[Effect of moderate salt restriction on the antihypertensive action of nifedipine: a double blind study]

Moderate salt restriction is of debatable efficacy in the treatment of mild or moderate hypertension; however, salt restriction enhances the activity of most antihypertensive drugs. Some observations suggest that the antihypertensive activity of calcium antagonists is not increased or could even decrease with dietary salt restriction. In the present work 15 patients suffering arterial hypertension and normal renal function are studied during four two week periods; a) unrestricted diet and medication, b) unrestricted diet and nifedipine (40 mg/day), c) low salt diet (5 g of salt/day) and nifedipine, and d) the same low salt diet, nifedipine and a salt supplement (6 g/day); salt or placebo were given in a double blind manner. At the end of each period arterial blood pressure was recorded, a urine sample for sodium determination was taken, and a blood sample was drawn for serum renine activity and biochemical parameters; at the end of each period patients' weight was recorded. Blood pressure significantly decreased (systolic: 9.83%, and dyastolic 11.17%) in patients treated with nifedipine, with no differences observed with salt modifications. Urinary sodium reflected correctly dietary salt modifications. Serum renine activity significantly increased during salt restriction. No significant changes were observed in weight or in the biochemical parameters studied. These results seem to suggest that the antihypertensive effect of nifedipine in patents suffering mild to moderate essential hypertension, with no change observed is not altered by the amount of salt in diet, at least within the limits studied (89.7 to 190 mEq/day of Sodium).