Calcium supplementation in salt-dependent hypertension.

To clarify the mechanism of the antihypertensive effect of oral Ca loading, we studied the effect of Ca supplementation on salt-induced blood pressure elevations in patients with essential hypertension and DOCA-salt hypertensive rats. When the diet was changed from low to high salt (300 mEq/day), the percent increase in mean blood pressure was smaller (p less than 0.01) in the Ca-supplemented (2,160 mg/day) patients than in the Ca-restricted (250 mg/day) ones. Oral Ca loading resulted in a smaller weight gain, a greater urinary sodium excretion, and an increase in red cell Mg. In the experimental study, high Ca (4% CaCl2) intake attenuated the blood pressure elevation in DOCA-salt-treated rats, accompanied with an increase in urinary sodium excretion, with the resultant attenuation in intra- and extracellular sodium retention. The decrease in catecholamine contents of hearts was improved, and a higher survival rate was observed in Ca-supplemented DOCA-salt rats. The results suggest that Ca supplementation may prevent a rise in BP in salt-dependent hypertension by inducing natriuresis with the resultant attenuation in sodium retention. The altered intracellular Mg level in hypertensive patients and the normalization of enhanced sympathetic nervous activity in DOCA-salt rats may, in part, be involved in its mechanism.