Regulation of ovarian steroidogenesis in vitro by follicle-stimulating hormone and luteinizing hormone during sexual maturation in salmonid fish

The regulation of ovarian steroidogenesis in vitro by coho salmon FSH and L H was investigated in intact coho salmon follicles and isolated follicular layers at various stages of oocyte maturation, from late vitellogenesis unt il the completion of germinal vesicle breakdown (GVBD). In granulosa layers from all stages, LH, but not FSH, stimulated 17 alpha,20 beta-dihydroxy-4- pregnen-3-one (17,20 beta-P) production. In theca-interstitial layers from all stages, FSH and LH stimulated steroid production, LH being more potent than FSH. The basal steroid output of intact follicles was significantly lo wer than that of isolated follicular layers, and their response to FSH and LH also differed. First, the intact follicles produced 17 alpha-hydroxyprog esterone in response to FSH during the central germinal vesicle stage while theca-interstitial layers did not. Second, estradiol-17 beta production wa s not inhibited by LH during final oocyte maturation in intact follicles, a s observed for granulosa layers. Our results indicate that LH is the determ ining factor regulating the production of the maturation-inducing steroid, 17,20 beta-P, and the induction of GVBD in the salmonid ovary. In summary, we have provided evidence for maturation-associated changes in the effects of FSH and LH in the salmonid ovary, which further supports the hypothesis that FSH and LH have distinct functions in the teleost ovary.