Modulation of prolactin receptors in cultured rat granulosa cells by FSH, LH and GnRH

Abstract

The hormonal modulation of prolactin (PRL)-binding capacity of rat granulosa cells was studied. Granulosa cells obtained from immature, hypophysectomized, estrogen-treated rats were cultured for 2 days in a serum-free medium in the presence of various hormones. FSH treatment in vitro stimulated granulosa cell PRL-binding capacity by ~ 4–6-fold in a dose-dependent manner. Concomitant treatment with 10 −8 M GnRH inhibited the FSH-induced increase in PRL-binding capacity by 64%. In contrast, the inhibitory effect of GnRH was blocked by concomitant treatment with 10 −6 M of a GnRH antagonist, [D-pGlu 1, D-Phe 2, D-Trp 3,6]GnRH. PRL-binding capacity was also increased (~2-fold) by in vitro treatment with cholera toxin (10 μg/ml). In granulosa cells pre-treated with FSH in vitro for 2 days, hCG treatment for 2 additional days stimulated PRL-binding capacity in a dose-dependent manner (~ 2-fold). Likewise, treatment with LH (100 ng/ml) also stimulated PRL-binding capacity by ~ 2-fold. These in vitro studies demonstrated that gonadotropins (FSH, LH and hCG) directly enhanced PRL binding by granulosa cells, whereas GnRH inhibited FSH action.