Effect of Ovariectomy on Pituitary Secretion of ACTH

Abstract

The effects of prepuberal gonadectomy on pituitary secretion of ACTH were studied in adult female rats. Plasma concentrations of ACTH in unstressed, adrenalectomized rats were decreased following ovariectomy to 76% (95% confidence limits 62–92%) of the control level. A comparable difference was also observed after the stress of ether anesthesia in rats with adrenals intact (57% of control; 95% confidence limits 46-76%). Unstimulated release of ACTH in vitro by whole pituitary glands from ovariectomized donors, with or without estradiol replacement, did not differ from that of control animals. Hypothalamic content of corticotropinrel easing activity (CRA) in intact and gonadectomized female rats was similar but was decreased in estradiol-injected, ovariectomized rats. The response of incubating pituitaries to uniform CRF stimulation was significantly depressed in the ovariectomized group (55% of control; 42–70%) and administration of 100 fig of polyestradiol phosphate partially reversed (81% of control; 65–96%) the decreased response. These data indicate that prepuberal ovariectomy results in decreased pituitary secretion of ACTH. The hyposecretion is related to a decreased sensitivity of the pituitary to CRF stimulation and a decreased pituitary capacity to synthesize ACTH. Moreover, the lower levels of plasma ACTH in adrenalectomized, ovariectomized rats suggest that the effects of estradiol are independent of corticosteroid feedback. (Endocrinology85: 1097, 1969)