The effect of an intravenous calcium load on serum total and ionized calcium in normotensive and hypertensive subjects.

Altered regulation of serum calcium level was proposed to be associated with arterial hypertension and to be dependent on a renal calcium leak or an altered calcium binding to plasma proteins and cell membrane described in human and experimental hypertension. The aim of this study was to analyze the regulation of serum total and ionized calcium levels during an intravenous calcium infusion (0.25 mmol calcium/kg body weight/hr for 2 hours) in a group of untreated essential hypertensives and a comparable normotensive group. Basal serum calcium concentrations did not differ between the two groups, whereas parathyroid activity and urinary calcium were significantly increased in hypertensive subjects. During the calcium load, serum calcium rose almost linearly in all subjects but with a reduced slope in the hypertensive group, which showed serum total and ionized calcium levels significantly lower than those of the controls at the end of the infusion. Our data indicate that hypertensive patients have an altered regulation of serum calcium concentrations, probably due to a different body distribution of calcium, rather than to an altered calcium binding to plasma proteins.