Interrelationship of Parathyroid and Adrenocortical Function in Calcium Homeostasis in the Rat

Abstract

This study evaluated the relationship between the parathyroid glands (PTG) and the adrenal cortex in calcium (Ca) homeostasis in the rat. Adrenalectomy (AdX) alone caused no change in plasma Ca. Thyroparathyroidectomy (TX-PTX) caused a decrease in plasma Ca within 4 hr. Concomitant AdX prevented this decrease. Cortisol 5 (img/100 g body wt SC immediately after surgery) caused a decrease in plasma Ca of TX-PTX plus AdX rats, but not of intact rats. Parathyroid extract (PTE) (single injection of 100 U/100 g body wt SC) caused less increase of plasma Ca in intact rats than i n AdX rats. PTE (125 U/100 g body wt SC twice daily for 2 days) to intact rats caused an increase in plasma Ca, adrenocortical hyperplasia and increase in plasma corticosterone. Cortisone acetate (10 mg SC twice daily for 7 days) to intact rats caused PTG hyperplasia and increase in serum immunoreactive parathyroid hormone (iPTH), but with no change in plasma Ca. The results show that a) PTH-induced hypercalcemia leads to increased adrenocortical function which partially inhibits the hypercalcemia, b) the hypocalcemic action of cortisol leads to increased parathyroid function which prevents significant hypocalcemia. Therefore, the data suggest that the parathyroid glands and the adrenal cortex act in concert in a compensatory manner to maintain the plasma Ca concentration within physiological limits. (Endocrinology95: 707, 1974)