In vitro pituitary responsiveness to gonadotropin-releasing hormone (LH-RH) in intact and castrated male and female rats

Abstract

The in vitro response of pituitaries isolated from both normal and 18–21-day post-castration male and female intact rats to incremental doses of synthetic gonadotropin-releasing hormone (LH-RH) has been investigated. Intact male pituitaries released luteinizing hormone (LH) maximally at the smallest dose of LH-RH (0.1 ng/ml) whereas intact female pituitaries released LH in a dose-response fashion. FSH release from intact male pituitaries was considerably greater than that from intact female pituitaries. As with LH, intact male pituitaries appeared maximally stimulated at 0.1 ng/ml of LH-RH. Intact female pituitaries did not release FSH until a 10 ng/ml dose of LH-RH was used. Male and female castrate pituitaries were more susceptible to LH-RH-induced LH and FSH release than were their intact counterparts, although this was more pronounced with regard to LH release. In addition castrate male pituitaries were more sensitive to lower doses of LH-RH than were castrate female pituitaries, this being most pronounced regarding LH release. Castrate female pituitaries released less FSH at the 100 ng/ml dose than at the 10 ng/ml dose, possibly indicating inhibition at these higher doses. In addition, pituitary extraction and serum from normal and castrate male and female rats were examined for LH and FSH content. LH content of castrated rat pituitaries of both sexes was considerably greater than that of their intact counterparts, as expected. However, castrate male pituitaries contained significantly less FSH than intact male pituitaries, whereas the opposite was true for the female groups. Serum LH and FSH levels were increased in the castrate groups with no difference between sexes. Serum from intact males contained considerably more FSH than did the serum from intact females.