The steroid synthesis pathway in the ovarian follicles of the red seabream during final oocyte maturation (FOM) was investigated by incubating intact follicles with different radioactively labeled steroid precursors. During FOM, the steroidogenic shift from estradiol-17β to 20β-hydroxylated progestin production occurred mainly due to a combination of inactivation of C17,20-lyase and activation of 20β-hydroxysteroid dehydrogenase. Of the steroids produced, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) exhibited the greatest effect on germinal vesicle breakdown (GVBD) in vitro. 17,20β-P was further converted to its 5β-reduced form, 17,20β-dihydroxy-5β-pregnan-3-one (17,20β-P-5β), which had lower GVBD activity, suggesting that 5β-reduction plays a role in the inactivation of the maturation-inducing ability of 17,20β-P. In contrast, no 5β-reduced metabolite of 20β-S was found. Serum levels of 17,20β-P and 20β-S, measured by ELISA, showed that circulating levels of both progestins increased during FOM, and 20β-S levels were approximately twice as high as 17,20β-P levels. This study clarified the complete steroidogenesis pathway during FOM in red seabream ovarian follicles and showed that two 20β-hydroxylated progestins, 17,20β-P and 20β-S, act as maturation-inducing hormones in this species. The catabolites of these two progestins and their physiological roles in reproduction are also discussed.
|Number of pages
|Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology
|Published - Sept 2002
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Animal Science and Zoology
- Molecular Biology