STEROID HORMONE ADMINISTRATION AND GONADOTROPHIN SECRETION IN THE GONADECTOMIZED RAT

Abstract

SUMMARY Facilitation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion by progesterone was demonstrated in female rats ovariectomized 1–2 months previously and primed with oestradiol benzoate or testosterone propionate 72 h before the second injection of steroid. The priming action of testosterone propionate may be due to conversion to oestrogen as the non-aromatizable androgen, 5α-dihydrotestosterone propionate, did not have this effect. None of the steroid hormone treatments tested facilitated LH or FSH release in male rats castrated as adults or in female rats rendered anovulatory by the injection of androgen or oestrogen on day 4 of postnatal life. This abnormality may be the functional basis of the anovulatory state in these animals. Of the progesterone derivatives tested in the oestrogen-primed ovariectomized rat only pregn-4-en-20α-ol-3-one and 5α-pregnane-3,20-dione significantly stimulated gonadotrophin secretion. These compounds, which are secreted by the rat ovary, may be involved, together with progesterone, in the initiation of the ovulatory surge of gonadotrophin during the oestrous cycle. The time-course of the changes in gonadotrophin release in the oestrogen-primed ovariectomized rat in response to progesterone was determined. An initial depression was followed by an increase which was more marked for LH than for FSH. Although sodium pentobarbitone administration will prevent or reverse progesterone-induced gonadotrophin secretion, no clear correlation could be established between the sequence of changes in gonadotrophin secretion observed in the present study and the changes in hypothalamic neuronal activity reported by others to follow similar treatment with steroid hormones.