Serum corticosterone in rats with delayed anovulation.

The purpose of this study was to investigate adrenal function in rats during the development of persistent oestrus to determine whether a change in blood levels of corticosterone would precede or coincide with the onset of infertility. The syndrome of delayed persistent oestrus and anovulation was induced by administration of a low dose (10 mug) of testosterone propionate (TP) at 5 days of age. Control animals were handled without injection or received the vehicle (sesame oil) only. Half of each group was ovariectomized at weaning and received Silastic implants of either oestradiol benzoate (OB) or cholesterol, 3 mm tube length/100 g body weight. Intact rats given the low TP dose showed precocious vaginal opening (27.3 +/- 2.1 days v. 37.6 +/- 2.4 (S.E.M.) days in unhandled controls) and ovulated within 2 days. Persistent vaginal cornification developed in 22 out of 26 rats by 75 days of age. The TP-treated rats had higher corticosterone values than the controls and did not show a further increase after OB implantation. Cholesterol implantation depressed corticosterone levels in the TP-treated rats. The effects of the low TP dose were not dependent upon gonadal function since they persisted in ovariectomized rats. The results suggest that early exposure to androgen can modify the sensitivity of the adrenal system to oestrogen, and can also lead to persistently high values of corticosterone which are not depressed by ovariectomy. These changes precede the onset of persistent oestrus.