Isolation of a novel maturation-inducing steroid produced in vitro by ovaries of Atlantic croaker.

All the steroids produced by Atlantic croaker ovaries during final oocyte maturation (FOM) were assayed for their ability to induce germinal vesicle breakdown (GVBD) of croaker oocytes in vitro. Ovarian tissue in the process of FOM was removed from Atlantic croaker (Micropogonias undulatus) and incubated with human chorionic gonadotropin (hCG) and pregnenolone in tissue culture medium for 8 hr. Steroids were extracted from the medium and fractionated by HPLC and TLC. Fractions were bioassayed for their potency to induce GVBD of Atlantic croaker oocytes in vitro. 17 alpha, 20 beta,21-Trihydroxy-4-pregnen-3-one (20 beta-dihydro-11-deoxycortisol, 20 beta-S) was identified as the predominant steroid product and the major maturation-inducing steroid produced by the ovary of Atlantic croaker in vitro. A small amount of another steroid with equal potency to induce GVBD was tentatively identified as 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P4); however, over ten times more 20 beta-S than 17 alpha,20 beta-P4 accumulated in the incubation medium. Trace amounts of testosterone and estradiol-17 beta were also isolated. Ovarian tissue incubated under more physiological conditions, without the addition of excess pregnenolone, failed to produce 17 alpha,20 beta-P4. These results provide further evidence that 20 beta-S is a major maturation-inducing steroid in Atlantic croaker.