Effect of Saline Infusion on Urinary Calcium Excretion in Essential Hypertension

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Abstract
Urinary excretion of sodium and calcium was examined in hypertensive (n = 8) and normotensive (n = 7) subjects following infusion of 2% saline at a rate of 11 mL/min for 90 min. The urinary sodium excretion was 204 ± 38 (mean ± SEM) µEq/min in normotensives and 233 ± 28 µEq/min in hypertensives before infusion of saline and increased maximally to 499 ± 114 µEq/min (P <.05) and to 928 ± 68 µEq/min (P <.01), respectively, after saline infusion. In normotensives, urinary calcium excretion did not change significantly; however, in hypertensives excretion increased markedly (P <.01) from 6.1 ± 0.7 µEq/min to 12.3 ± 1.6 µEq/min. Plasma atrial natriuretic peptide (ANP) levels increased significantly (P <.05) in both groups. Serum ionized calcium and plasma parathyroid hormone (PTH) levels did not change significantly. The increments as well as the preinfusion plasma PTH level, were significantly (P <.05) higher in hypertensives than in normotensives. The present study showed that exaggerated natriuresis was accompanied by hypercalcinuria and an enhanced rise in plasma ANP in hypertensives. Basal levels of plasma PTH were elevated in hypertensives. The calcium deficiency may be attributable to a close relationship between urinary sodium and calcium, and causally related to the disturbance of sodium and volume homeostasis in hypertension, which results in exaggerated natriuresis. Am J Hypertens 1990;3:113–118

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