Pituitary Responsiveness to LH-RH in Intact and Ovariectomized Androgen-Sterilized Rats

Serum LH changes in response to LH-RH injection were measured in intact and ovariectomized, steroid-treated female rats which were androgenized neonatally with 1,250 microgram testosterone propionate (TP) on day 5. At a dose of 20 ng LH-RH/100 g b.w., serum LH levels in intact rats increased over pre-injection levels, and at a dose of 100 ng LH-RH/100 g b.w., LH concentrations 15 min after injection were higher in nembutal-blocked proestrous rats than in androgen-sterilized rats. However, the ovulation response was not different between the groups. In ovariectomized estradiol benzoate (EB)-treated, androgen-sterilized rats, serum LH concentrations 15 and 60 min after LH-RH injection were lower than in similarly treated control rats. This effect was not secondary to the anovulatory state of the animal, since it also occurred in ovariectomized EB-treated prepuberal rats and in rats ovariectomized prepuberally and treated with EB in adulthood. Also, after treatment with 5alpha-dihydrotestosterone propionate (5alpha-DHTP), pituitary responsiveness to LH-RH in androgen-sterilized rats was lower than in control rats, which suggests that the subnormal response in the estrogen-treated rats was not due to a relative insensitivity to estrogen in the androgen-sterilized rats. The relatively high pituitary responsiveness to LH-RH in intact androgen-sterilized rats is probably due to the high circulating estrogen levels. The subnormal pituitary responsiveness to LH-RH after ovariectomy and estradiol treatment suggests, in addition to an effect on the hypothalamus, also a direct effect of neonatal androgen administration on the pituitary.