EFFECTS OF ESTRADIOL-17-BETA ON FSH-STIMULATED STEROIDOGENESIS IN CULTURED MARMOSET GRANULOSA-CELLS

A role for oestradiol in ovarian follicular development is well recognized. However, a number of disparate effects have been reported for the action of oestradiol in the primate ovary. To investigate this further, we have examined the effects of oestradiol on the differentiation of granulosa cells isolated from small (0.5-1 mm) antral follicles obtained from the ovaries of prepubertal marmoset monkeys (Callithrix jacchus). Granulosa cells were co-cultured with oestradiol and human FSH (hFSH) for 48 h, or were pretreated with oestradiol for 48 h before addition of gonadotrophin for a further 48 h. Oestradiol (0.01-100 nmol/l) had no effect on basal or hFSH-stimulated progesterone accumulation and aromatase activity when the hormones were added concurrently. Furthermore, oestradiol did not influence the ability of hFSH to induce LH/human chorionic gonadotrophin (hCG) responsiveness in immature granulosa cells. The absence of synergism between oestradiol and hFSH in the induction of marmoset granulosa cell differentiation was independent of the presence of phenol red in culture medium. However, gonadotrophin-stimulated steroidogenesis was attenuated when cells were cultured in the presence of phenol red compared with in its absence; this effect was more pronounced for gonadotrophin-stimulated aromatase activity but was evident for LH/hCG-stimulated progesterone accumulation at higher doses of hCG (10 and 100 ng/ml). An effect of phenol red on basal steroidogenesis was less obvious. In contrast, pretreatment of granulosa cells with oestradiol (0.1-mu-mol/l) alone for 48 h resulted in a greater steroidogenic response to hFSH (P < 0.001) and dibutyryl cyclic AMP (P < 0.01) treatment during a second 48-h culture period compared with cultures pretreated with dihydrotestosterone (0.1-mu-mol/l), hFSH (30 ng/ml) or without hormones. This stimulatory effect of oestradiol appeared to be specific in that it was antagonized (P < 0.05) by the anti-oestrogen tamoxifen (1-mu-mol/l). In conclusion, this study provides evidence for a stimulatory autocrine role of oestradiol in the primate ovary. However, the action of oestradiol appears not to synergize with FSH directly, but rather to increase FSH-stimulated steroidogenesis by an independent mechanism.