CIRCULATING LEVELS AND IN-VITRO PRODUCTION OF 2 MATURATION-INDUCING HORMONES IN TELEOST - 17-ALPHA,20-BETA-DIHYDROXY-4-PREGNEN-3-ONE AND 17-ALPHA,20-BETA,21-TRIHYDROXY-4-PREGNEN-3-ONE, IN A DAILY SPAWNING WRASSE, PSEUDOLABRUS-JAPONICUS

The female bambooleaf wrasse, Pseudolabrus japonicus, spawns daily dur ing the spawning season, and exhibits a diurnal rhythm of ovarian deve lopment. In the present study, we have investigated: (1) circulating l evels of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) and 17 alpha,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta-S) in females sampled at different times of the day during spawning season in capti vity, and (2) in vitro production of 17,20 beta-P and 20 beta-S by fol licle-enclosed oocytes at seven different developmental stages. In add ition, we developed a microtiter plate enzyme-linked immunosorbent ass ay (ELISA) for 17,20 beta-P. Serum levels of 17,20 beta-P and 20 beta- S showed similar diurnal changes; substantial increases in these level s occurred around the time of germinal vesicle breakdown (GVBD). In vi tro experiments showed that massive production of 17,20 beta-P and 20 beta-S occurred in follicles collected just before or during GVBD. Fur ther, acute decreases in 17,20 beta-P and 20 beta-S production were fo und in the ovarian follicles just prior to ovulation, suggesting inact ivation of the maturation-inducing hormone (MIH). These results, taken together with our previous data on the occurrence of GVBD in vitro, s uggest a role for both 17,20 beta-P and 20 beta-S as MIHs in the bambo oleaf wrasse.