Effect of oral calcium supplementation on intracellular calcium and plasma renin in men

Abstract

Abstract A double-blind, placebo-controlled parallel study was conducted on the effect of a high daily oral calcium supplementation of 1 g elemental calcium, given twice daily for 16 weeks in normal male subjects, on plasma renin, aldosterone, kallikrein, cGMP, cAMP and calciotropic hormones, intracellular calcium concentrations and plasma total and ionized calcium. After a 1-month run-in period on a limited use of dairy products, the subjects (n=32) were allocated to a placebo or a calcium group. Placebo or 1 g elemental calcium was administered twice daily in the morning and evening for 16 weeks. All subjects were investigated at baseline and after 1, 2, 4, 8 and 16 weeks of placebo or calcium administration. A decreased intraerythrocyte and intraplatelet Ca2+ concentration was observed in the calcium-treated subjects. Compared with the placebo group, an increase in the plasma renin activity (PRA) in the calcium group was observed after 4, 8 and 16 weeks of oral calcium administration. However, plasma aldosterone and urinary excretion of aldosterone, kallikrein, cGMP and cAMP were not changed during calcium administration. Oral calcium supplementation in these men was also accompanied by a reduction in the plasma concentration of intact parathyroid hormone and 1,25-dihydroxyvitamin D3, an increase in 24-h urinary calcium excretion but no change in the plasma total Ca2+ concentration, serum ionized Ca2+ level and plasma phosphate or 25-hydroxyvitamin D3. Lacidipine tended to increase PRA in the placebo-treated subjects and to decrease it in the calcium-treated subjects: this difference in lacidipine effect between the placebo and calcium group was significant (P<0·05). Our data show that the increase in PRA observed in men during oral calcium supplementation is accompanied by a reduction in the intracellular free and total Ca2+ concentration in platelets and erythrocytes and by a decrease in the plasma concentration of intact parathormone and 1,25-dihydroxyvitamin D3. Journal of Endocrinology (1995) 146, 421–429