STEROIDOGENESIS OF CHICKEN GRANULOSA AND THECA CELLS - INVITRO INCUBATION SYSTEM

An in vitro incubation system has been developed to study the steroidogenic capability of the theca or granulosa cells in the postovulatory and 3 largest preovulatory follicles of chickens. Follicles were collected at different times during the hen's 26 h laying cycle taking into consideration the endogenous plasma LH peak(s). Three major sex steroids, progesterone (P), estrogen (E) and testosterone (T), produced by these follicular cells were measured by radioimmunoassay. Granulosa cells isolated from pre- or postovulatory follicles spontaneously synthesized large amounts of P and little T. In contrast, theca cells collected from the same follicles did not produce any sex steroids. The influence of endogenous gonadotropins on steroidogenesis of these follicular cells incubated in vitro was seen only in the P synthesis by granulosa cells of the largest preovulatory follicles: P synthesizing ability was significantly greater in follicles collected at the time of preovulatory LH surge than those collected at any other times studied. Interestingly, granulosa cells of smaller (more immature) follicles, in general, showed greater ability to synthesize P and T than did the first largest which is destined to ovulate next. These findings provide direct evidence that granulosa cells of both pre- and postovulatory follicles are steroidogenically active and spontaneously synthesize P and T. In contrast, the role of theca cells in follicular steroidogenesis remained unclear. Data of this study also strongly suggest that the postovulatory follicle of hens, which does not morphologically develop into a corpus luteum, should be considered as an active endocrine tissue.