Some Effects of Intravenously Administered Calcium on Inorganic Phosphate Metabolism

Abstract

The intravenous administration of calcium gluconate to normal subjects results in a diminution in the urinary excretion of P. This phenomenon occurs as a result of increased renal tubular reabsorption of phosphate. This effect of administered Ca appears to require normally functioning parathyroid glands, since it is not seen in patients with profound hypoparathyroidism or hyperparathyroidism, and it can be abolished in normal subjects by the prior administration of parathyroid extract. No change, or even an elevation in P excretion occurs during the administration of Ca. Hence, more striking reductions in P excretion are detected if urine is collected during the 8-24 hours after the four-hour infusion of Ca is begun, and compared with the corresponding period on the control day. The response of urinary P excretion to Ca administration does not appear to be a sensitive test for hypoparathyroidism, since patients with clinically apparent, but mild hypoparathyroidism may show a pattern similar to that of normal subjects. The percentage of administered Ca retained by a given indicidual is quite constant on repeated testing. However, unexplained variability occurs in the amount retained by different subjects. The intravenous infusion of Ca leads to a prompt rise in plasma phosphate in almost all subjects. The rise occurs before there is any reduction in urinary excretion of P, and hence must represent mobilization from intracellular stores. In some individuals large doses of parathyroid extract abolish this elevation of plasma P.