Ovarian steroid synthesis during oocyte maturation and ovulation in Japanese catfish (Silurus asotus)

Several aspects of the endocrine regulation of final oocyte maturation (FOM ) and ovulation in Japanese catfish (Silurus asotus), was investigated. The se were: (1) potency of various steroids on inducing FOM in vitro, (2) ster oid production stimulated with human chorionic gonadotropin (hCG) in vitro, (3) effectiveness of hCG administration in vivo on inducing FOM and ovulat ion, and (4) plasma sex steroids profiles in female catfish during FOM and ovulation induced by hCG injections. Among steroids tested, 17,20 beta -dih ydroxy-4-pregnen-3-one (17,20 beta -P) was the most potent steroid in induc ing FOM and 17,20 beta ,21-trihydroxy-4-pregnen-3-one (20 beta -S) was the second most effective. 17 alpha -hydroxyprogesterone (17 alpha -P) and 11-d eoxycortisol (11-DC) did not induce FOM even at the highest dose tested. Bo th ovarian 17,20 beta -P and 20 beta -S production were induced by hCG in v itro and the 17,20 beta -P production was higher than 20 beta -S production . The ovarian fragments cultured in vitro did not convert 17 alpha -P to 17 ,20 beta -P unless they were treated with hCG. hCG injection increased plas ma 17,20 beta -P and 20 beta -S levels, causing FOM and partial ovulation. In addition, this hCG-induced 17,20 beta -P production was higher than the 20 beta -S production in vivo. These data suggest that 17,20 beta -P appear s to be a major maturation-inducing steroid (MIS) in Japanese catfish and t hat MIS production may be regulated by GTH-induced activation or synthesis of 20 beta -hydroxysteroid dehydrogenase. (C) 2001 Elsevier Science B.V. Al l rights reserved.