Activin-A differentially regulates steroidogenesis by sheep granulosa cells

Intra-ovarian factors, such as activin, are implicated in multiple aspects of follicular development in mammalian ovaries. This study was conducted to investigate a possible effect of activin-A on steroidogenesis in sheep gra nulosa cells in vitro. Sheep granulosa cells were obtained from medium antr al follicles and cultured in a chemically defined RPMI-1640. Oestradiol and progesterone production, secreted by the cultured cells, was evaluated by enzyme-linked immunosorbent assay. In order to determine the dose effect of activin-A on steroidogenesis, granulosa cells were cultured in the presenc e of increasing concentrations of activin-A (0, 0.5, 5 and 50 ng ml(-1)) fo r 48 hours. The results revealed that activin-A exerts a differential effec t on steroidogenesis in granulosa cells in such a way that it significantly (P < 0.05) suppressed progesterone production and enhanced oestradiol prod uction. These results were confirmed by the time effect of activin-A on oes tradiol and progesterone production in granulosa cells. In the absence of a ctivin-A treatment, granulosa cells showed enhanced capacity to produce pro gesterone, but not oestradiol, as the time progressed from 12 to 48 hours. Treatment of sheep granulosa cells with 25 ng ml(-1) activin-A for 12, 24 a nd 48 hours significantly stimulated oestradiol production but inhibited pr ogesterone production. These results suggest that activin-A is a local regu lator of sheep folliculogenesis that might act to support differentiation i n granulosa cells and suppress luteinisation. (C) 2001 Harcourt Publishers Ltd.