Steroidogenesis in the Ovarian Follicles of the Medaka (Oryzias latipes) during Vitellogenesis and Oocyte Maturation

Changes in the steroidogenic pathway in medaka (Oryzias latipes) ovarian follicles during vitellogenesis and oocyte maturation were investigated in vitro by incubation of follicles with several radiolabeled steroid precursors, followed by thin layer chromatography (TLC) fractionation and recrystallization. When vitellogenic follicles collected at 18 hr before the expected time of spawning were incubated with 3H-labeled pregnenolone, the major metabolites were 17α-hydroxypregnenolone, 17α-hydroxyprogesterone, and androstenedione. Incubations of vitellogenic follicles with androstenedione produced testosterone and estradiol-17β By contrast, when maturing follicles (postvitellogenic follicles undergoing maturation) collected at 10 hr before spawning were incubated with 3H-labeled pregnenolone, the major metabolites were 17α-hydroxypregnenolone, 17α-hydroxyprogesterone, and 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DP, maturation-inducing hormone of medaka); androstenedione was not detected. Neith...