title: Development of the steroidogenic capacity of medaka (Oryzias latipes) ovarian follicles during vitellogenesis and oocyte maturation.
abstract: Developmental changes in the steroidogenic capacity of medaka, Oryzias latipes, ovarian follicles at 12 different stages during vitellogenesis and oocyte maturation were examined using 18-hr incubations. Medaka were acclimated to conditions of 26 degrees on a lighting regime of 14 hr light and 10 hr dark. Under these conditions, females usually spawn daily within 1 hr of the onset of light. The process of vitellogenesis and oocyte maturation occurs within 72 hr, the breakdown of the germinal vesicle (GVBD) and ovulation being completed at 6 and 1 hr, respectively, before the expected time of spawning. Vitellogenic follicles between 32 and 16 hr before spawning produced large amounts of estradiol-17 beta spontaneously and in response to partially purified chum salmon gonadotropin (SGA) or pregnant mare's serum gonadotropin (PMSG). However, postvitellogenic follicles between 12 and 4 hr before spawning showed very little evidence of estradiol-17 beta production. By contrast, basal concentrations of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-diOHprog) remained very low in follicles during vitellogenesis and were elevated in those collected during oocyte maturation; there was a close relationship between the medium concentration of 17 alpha,20 beta-diOH-prog and the percentage GVBD in the oocytes. 17 alpha,20 beta-DiOHprog production in response to PMSG was very low in follicles during early and mid-vitellogenesis and increased in those collected at 28 hr before spawning, a time which coincided with the first acquisition of the ability of the follicles to undergo maturation in response to gonadotropin. These results clearly demonstrate that a distinct shift from the secretion of predominantly estradiol-17 beta to the secretion of 17 alpha,20 beta-diOHprog occurs in the medaka ovarian follicle immediately prior to oocyte maturation. Considering the potency of 17 alpha,20 beta-diOHprog for the induction of oocyte maturation in vitro, these results further suggest that 17 alpha,20 beta-diOHprog is a naturally occurring steroidal mediator of oocyte maturation in the medaka.
mesh_terms: D000818:Animals; D003532:Cyprinodontiformes / Q000502:physiology*; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006062:Gonadotropins / Q000494:pharmacology*; D006064:Gonadotropins, Equine / Q000494:pharmacology; D006908:Hydroxyprogesterones / Q000378:metabolism; D009865:Oocytes / Q000254:growth & development*; D009990:Oryzias / Q000502:physiology*; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D011863:Radioimmunoassay; D013256:Steroids / Q000378:metabolism*; D013997:Time Factors; D014818:Vitellogenesis / Q000187:drug effects*
chemical_list: D006062:Gonadotropins; D006064:Gonadotropins, Equine; D006908:Hydroxyprogesterones; D013256:Steroids; C016844:salmon gonadotropin; C021012:17 alpha,20 beta-dihydroxypregn-4-en-3-one; D004958:Estradiol