Changes in ovarian steroidogenesis in vitro associated with final maturation of Atlantic croaker oocytes.

Changes in ovarian steroidogenesis during final oocyte maturation (FOM) in the Atlantic croaker (Micropogonias undulatus) were investigated in vitro by incubation of oocytes with tritiated pregnenolone, followed by chromatographic separation of the radioactive steroid products. Testosterone and estradiol-17 beta were the major tritiated steroids produced by the ovary before the onset of FOM. Induction of FOM by human chorionic gonadotropin, both in vivo and in vitro, coincided with the appearance of 17 alpha,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta-S) as the predominant steroid product. The production of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one and 11-deoxycorticosterone, maturation-inducing steroids previously proposed for other teleost species, could not be demonstrated in Atlantic croaker ovaries during FOM. The timely synthesis of 20 beta-S in croaker at the onset of oocyte maturation provides further evidence for a physiological role of 20 beta-S in the induction of FOM in this species.