Simultaneous Effects of Estradiol on TSH Secretion and Adrenocortical Function in Male and Female Rats

Abstract

Sex differences in TSH secretion and adrenal function were revealed in adult male and female Sprague-Dawley rats after chronic administration (14 days) of estradiol benzoate (EB). The effect of the steroid on the pituitary-thyroid and adrenocortical systems was dose dependent. Relatively little change in the various indices of adrenal function (gland weight, plasma and adrenal corticosteroids) was seen in the female rat with all dose levels of EB treatment (.1, 1, 10 and 50 [mu]g daily). TSH content of the enlarged pituitary progressively declined, however. Plasma TSH titers also fell. This was accompanied by histological alterations indicative of reduced secretion in the thyroid. The response of the adrenal in estradiol-treated male rats was bi-phasic. Lower doses (10 and 50 [mu]g) produced adrenal hypertrophy and sharp elevation in plasma and adrenal corticosteroid concentrations. With higher doses of EB (150 [mu]g), all indices of adrenal activity remained normal. TSH content of plasma and adenohypophysis was not significantly altered in the male rat despite the rise and fall in corticosteroid levels. The findings support the view that estrogen influences anterior pituitary secretion via multiple loci and mechanisms of action. The suppression of TSH secretion in the female with chronic EB administration is believed to involve a primary disturbance in the feedback relationship between thyroid and hypophysis.