Effect of follicular fluid and oestradiol on the luteinization of rat granulosa cells in vitro.

The effect of pig follicular fluid (FF), total or oestrogen-free, and of oestradiol-17 beta on the luteinization and progesterone secretion of rat granulosa cells was investigated during 4 days in culture. Both FF and oestrogen-free FF modified the differentiation of the granulosa cells, particularly their size and the appearance of their nucleoli. Addition of total FF or oestradiol-17 beta (50, 100 or 500 ng/ml) to the control medium markedly increased the progesterone secretion of the granulosa cells, but oestrogen-free FF and dialysed fetal calf serum had no effect. It was concluded that (1) FF could modify the morphological changes of the rat granulosa cells in vitro, but could not inhibit their secretion of progesterone, (2) the granulosa cells were able to synthesize progesterone regardless of their stage of differentiation, (3) oestradiol 17 beta had a direct stimulatory effect on progesterone secretion by granulosa cells in vitro. The possible mode of action of FF upon luteinization is discussed.