Effect of Intravenous Calcium Infusion on Indices of Activity of the Parathyroid Glands and on Urinary Calcium and Sodium Excretion in Normotensive and Hypertensive Subjects

Abstract

The effect of an intravenous calcium gluconate load (10 mg/kg over 5 min) on plasma ionized calcium concentration, parathyroid hormone (PTH), and the rate of urinary excretion of calcium, sodium, and nephrogenous cyclic adenosine monophosphate (NcAMP) was examined in 26 patients with essential hypertension and 27 age- and sex-matched normotensive subjects. Prior to calcium administration hypertensives had lower plasma ionized calcium concentration (P < .01) and higher PTH levels (P < .001) and excreted more calcium (P < .05) and NcAMP (P < .001) in the urine compared to normotensives. Following calcium infusion, plasma ionized calcium did not differ significantly between the two groups, but PTH levels remained higher in the hypertensive subjects at both 60 min (P < .001), and at 120 min (P = .02) post-load. Post-load values for both urinary calcium excretion and urinary sodium excretion were significantly higher in the hypertensive subjects than in the control group. Both before and after calcium infusion, urinary calcium excretion was positively correlated with urinary sodium excretion in each of the two groups, but for the same level of sodium excretion, hypertensives excreted more calcium in the urine, compared to normotensives, both before (P < .05) and after calcium infusion (P < .001). A positive correlation between basal plasma renin activity (PRA) values and plasma ionized calcium values obtained before (r = 0.42, P = .03) or at 60 min (r = 0.41, P = .03) and 120 min (r = 0.42, P = .03) after calcium infusion existed only in the hypertensive subject group. Post-load urinary sodium excretion values were negatively correlated to basal PRA values in both groups (r = -0.55, P < .01 and r = -0.58, P < .01 for hypertensives and normotensives, respectively), but a similar negative correlation between post-load urinary calcium excretion values and basal PRA values existed only in the hypertensive subject group (r = -0.50, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)