Effect of Glucocorticoids on Function of the Parathyroid Glands in Man

Abstract

This study evaluated the effect of chronic and acute administration of excessive doses of glucocorticoids on parathyroid hormone (PTH) secretion in man. Eleven patients receiving 15 to 80 mg prednisone daily for 1 to 50 months had normal serum calcium (Ca) but serum PTH levels significantly greater than those of 19 controls. Eleven normal adult men received 200 mg cortisol iv over a 4-hr period, during and following which blood was obtained frequently for serum Ca and PTH. Serum Ca remained normal in all patients. PTH began to rise by ¼ hr, was 152 ± 18.5% of baseline by 1 hr, reached 172 ± 18.5% of baseline by 3 hr, and then gradually declined to 126 ± 12.6% of baseline at 6 hr. These data indicate that in man, as in the rat (shown in previous studies), increase in cortisol with its hypocalcemic effect, causes stimulation of the parathyroid glands (PTG) with increased PTH secretion, which prevents significant hypocalcemia. This parathyroid response is prompt (as indicated by the cortisol infusion study), and also persistent (as indicated by the long-term steroid treatment study). These observations support the conclusions from prior studies that the adrenal cortex, in addition to the PTG, is important in Ca homeostasis. The observations also suggest that bone loss due to excessive glucocorticoids may be partially caused by induced PTH excess.