Sites of steroid production in ovine graafian follicles in culture.

The follicular components responsible for the synthesis of oestrogen, testosterone, and progesterone have been localized by studying in vitro the steroidogenic capacity of (1) intact follicles, (2) opened but undisturbed follicle walls, (3) isolated thecal shells, (4) granulosa cells and (5) co-cultures of thecal shells and granulosa monolayers. Oestrogen was secreted throughout the five-day culture period by intact follicles and explants of follicle wall. Neither the isolated thecal shell nor the membrana granulosa alone secreted oestrogen in vitro, but granulosa cells converted exogenous testosterone to oestrogen during the first few hours after explantation. A limited and transient production of oestrogen occurred in co-cultures of theca and granulosa. Testosterone was secreted in the presence of FSH in approximately equal amounts by intact follicle, follicle wall and thecal shells. No testosterone was secreted by the isolated granulosa cells. Progesterone was secreted by each cellular component but the highest output occurred where granulosa cells were grown in monolayer culture. The results indicate that the theca is the source of follicular androgen synthesis but that an interaction between theca and granulosa is required for the production of oestrogen. It is postulated that direct contact between two cell components is important in the modulation of steroidogenic function within the follicle.