Neonatal ovariectomy and pituitary-adrenal responsiveness in the adult rat

Litters of female rat pups were handled daily from birth to weaning. When 12 days old the pups were ovariectomized or received sham surgery. At 70 days sham and ovariectomized animals were decapitated immediately or placed within a novel environment for 10, 20, or 40min before decapitation. Basal plasma levels of androstenedione in ovariectomized animals were approximately half that of intact sham controls, and stress caused only a small rise in androstenedione in this group. Androstenedione levels in ovariectomized animals were consistently at or below the lower sensitivity of the radioimmunoassay, indicating that circulating levels of androstenedione in the female rat are primarily of ovarian origin. Basal ACTH and corticosterone levels did not differ significantly between the two groups. However, stress-induced levels of ACTH and corticosterone were significantly depressed in ovariectomized subjects compared to controls following exposure to the novel environment. Furthermore, while ACTH levels started to return to baseline by 40min in controls, this effect was not observed in ovariectomized animals. These findings demonstrate that prepubertal removal of ovarian humoral factors can have a long-term impact on the responsiveness of the hypothalamic-pituitary-adrenal axis to stress.