Inhibitory Effects of Induced Hypercalcemia on Secretion of Parathyroid Hormone*

Abstract

Phosphate clearance (Cp) was measured before and 8 to 10 hours after the induction of hypercalcemia in euparathyroid and hyperparathyroid subjects. In patients with phosphaturia of secondary hyperparathyroidism the Cp fell to within the normal range after standard calcium infusion, whereas in the phosphaturia of intrinsic renal tubular disease no such change occurred. In euparathyroid subjects, calcium infusion resulted in a significant fall in Cp even when the control values were above the levels considered normal. In hyperparathyroidism with parathyroid tumor, an insignificant fall in Cp followed induction of increased hypercalcemia, even when the control levels of Cp were normal or slightly elevated. Preliminary studies indicate that in hypercalcemic states other than hyperparathyroidism, induction of further elevation of the serum calcium level does not reduce Cp. This technique of study provides a much sharper definition of change in phosphorus excretion than does the use of 24-hour measurements.