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Steroid metabolism by ovarian follicles of the sea bass Dicentrarchus labrax
Institution:1. Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal;2. Center for Aquaculture Research, Agro-Technological Institute of Castilla y Leon, Ctra. Arévalo, s/n. 40196 Zamarramala, Segovia, Spain;3. Marine Genomics Group, Faculty of Biosciences and Aquaculture, Nord University, 8049 Bodø, Norway;4. Planta de Cultivos el Bocal, Spanish Institute of Oceanography (IEO), Barrio Corbanera, s/n 39012, Monte, Santander, Spain;5. SPAROS Ltd, Área Empresarial de Marim, Lote C, 8700-221 Olhão, Portugal;6. Department of Biomedical Sciences and Medicine, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal;7. Algarve Biomedical Center (ABC), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal;1. Deltares, PO Box 177, 2600 MH Delft, The Netherlands;2. Department of Civil Engineering, Ghent University, Technologiepark 904, B-9052 Zwijnaarde, Belgium;1. Department of Environment Sciences, University of California, Riverside, CA 92521, USA;2. California Surface Water Ambient Monitoring Program, Moss Landing Marine Labs, Moss Landing, CA 95039, USA
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 μg sea bass hypophysis plus 50 ng 17-hydroxyprogesterone (17-P), (2) 20 μg 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, 17,20β-P, or 17,20β,21-P. Free and conjugated (sulfates and glucuronides) levels of the established teleost oocyte maturation inducing steroids (MIS), i.e. 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) were measured in the incubation media by high performance liquid chromatography. Our results show that the synthesis of free and conjugated 17,20β-P is constant (0.1–0.2 ng/ml) in all incubates. In contrast, the synthesis of free and conjugated 17,20β,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 17,20β-P and 17,20β,21-P are equally potent and highly effective. These results demonstrate that 17,20β-P and 17,20β,21-P are synthesized in vitro by follicles of sea bass and that sulfation is the main route for the metabolism of the C21-steroids in riper follicles. The highest levels of 17,20β,21-P, found in incubates containing stage II follicles, points at 17,20β,21-P, rather than 17,20β-P, as the most probable MIS in sea bass, nonetheless, this hypothesis requires further confirmation.
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