title: Steroid metabolism by ovarian follicles of the sea bass Dicentrarchus labrax.
abstract: Ovarian samples from fear sea bass, Dicentrarchus labrax, were collected for the in vitro incubations during the spawning period. Follicles with fully developed vitellogenic oocytes showing central germinal vesicle (stage I follicles) and follicles with oocytes showing initial germinal vesicle migration (stage II follicles) were treated with either (1) 20 microg sea bass hypophysis plus 50 ng 17-hydroxyprogesterone (17-P), (2) 20 microg hypophysis alone, (3) 50 ng 17-P alone and (4) media alone. Structure-activity experiments used stage II follicles treated with several dosages (0.1, 1.0 and 10.0 ng/ml) of either 17-P, 17,20beta-P, or 17,20beta,21-P. Free and conjugated (sulfates and glucuronides) levels of the established teleost oocyte maturation inducing steroids (MIS), i.e. 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) and 17,20beta,21-trihydroxy-4-pregnen-3-one (17,20beta,21-P) were measured in the incubation media by high performance liquid chromatography. Our results show that the synthesis of free and conjugated 17,20beta-P is constant (0.1-0.2 ng/ml) in all incubates. In contrast, the synthesis of free and conjugated 17,20beta,21-P is higher in incubates containing stage II follicles (up to 5 ng/ml) than in those having stage I follicles (up to 3 ng/ml; P<0.01). Structure-activity data reveal that 17-P is not effective at inducing in vitro germinal vesicle breakdown whereas both 17,20beta-P and 17,20beta,21-P are equally potent and highly effective. These results demonstrate that 17,20beta-P and 17,20beta,21-P are synthesized in vitro by follicles of sea bass and that sulfation is the main route for the metabolism of the C(21)-steroids in riper follicles. The highest levels of 17,20beta,21-P, found in incubates containing stage II follicles, points at 17,20beta,21-P, rather than 17,20beta-P, as the most probable MIS in sea bass, nonetheless, this hypothesis requires further confirmation.
authors.affiliation: High Institute of Health Sciences-North, Paredes, Portugal.
authors.forename: M J
authors.initials: MJ
authors.lastname: Rocha
authors.forename: M A
authors.initials: MA
authors.lastname: Reis-Henriques
mesh_terms: D019326:17-alpha-Hydroxyprogesterone / Q000378:metabolism; D000818:Animals; D001492:Bass / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006908:Hydroxyprogesterones / Q000378:metabolism; D009865:Oocytes / Q000502:physiology; D006080:Ovarian Follicle / Q000378:metabolism*; D013256:Steroids / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D006908:Hydroxyprogesterones; D013256:Steroids; C021012:17 alpha,20 beta-dihydroxypregn-4-en-3-one; D019326:17-alpha-Hydroxyprogesterone