Pituitary-adrenal function in thyroparathyroidectomized male and female rats.

The influence of thyroid hormones on pituitary-adrenal function was assessed by studying several aspects of adrenocortical function approximately 30 days after thyroparathyroidectomy (TPTx). Both male and female rats showed evidence of rhythmic adrenocortical activity; peak plasma corticosterone levels occurred just before the dark phase of the lighting schedule. Only the amplitude of the rhythm appeared altered by TPTx. Peak plasma corticosterone levels in TPTx male and female animals were less (P less than 0.05) than corresponding levels in intact control rats. Both sexes showed significant responses to stress, but the morning stress response in TPTx females was less (P less than 0.01) than the stress response in intact controls. Concomitant with the reduced stress response, the adrenocortical response to exogenous ACTH was reduced in TPTx female rats.