Effect of oral calcium on blood pressure response in salt-loaded borderline hypertensive patients.

Abstract

To clarify the mechanism of the antihypertensive effect of oral calcium loading, we studied the effect of low versus high calcium intake on salt-induced blood pressure elevations in patients with borderline hypertension. After a 7-day period of dietary salt restriction (50 meq/day), 27 patients were placed ona high salt (300 meq/day), low calcium (250 mg/day) diet for 7 days; 14 of these patients were given 2,160mg/day of supplementary calcium (Ca group), and 13 patients were given placebo (non-Ca group). With a high salt intake, the present increase in mean blood pressure was smaller in the Ca group than in the non-Ca group (+2.85 .+-. 1.22% + 8.63.+-. 1.66%, respectively, p< 0.01). The Ca group showed a smaller weight gain (p < 0.05)and a greater urinary excretion of sodium (p < 0.005) than the non-Ca group. In the Ca group, but not in the non-Ca group, high salt intake resulted in an increase in intraerythrocyte magnesium content (p < 0.01), which was correlated inversely with the salt-induced changes in mean blood pressure (r = -.054, p < 0.05). While the increase in cellular magnesium was greater in the Ca group, changes in red blood cell sodium and sodium/potassium ratio were not different between the two groups. The results suggest that oral calcium supplementation may prevent a rise in blood pressure in patients on a high salt, low calcium diet by attenuating the sodium retention. The intracellular magnesium level may, in part, be involved in the regulation of salt-induced blood pressure response, although the pathophysiological mechanism remained unexplored.