17α,20β,21-Trihydroxy-4-pregnen-3-one: the probable maturation-inducing steroid of the Lusitanian toadfish |
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Authors: | T Modesto A V M Canário |
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Institution: | Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8000-810 Faro, Portugal |
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Abstract: | 17,20β,21-Trihydroxy-4-pregnen-3-one (17,20β,21-P) was identified as the major metabolite of incubations of Lusitanian toadfish Halobatrachus didactylus ovarian follicles with 3H]-17hydroxyprogesterone. The potency of several steroids in inducing germinal vesicle breakdown of follicle-enclosed oocytes of Lusitanian toadfish was systematically examined by using an in vitro germinal vesicle breakdown (GVBD) bioassay. 17,20β-Dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-P, two confirmed maturation-inducing steroids (MIS) in teleosts, were the most potent in inducing GVBD with ED50s ranging between 9 and 271 nM. Structure-activity relationships followed similar patterns to what has been observed in similar bioassays, i.e. a vital requirement for 17- and 20β-hydroxyl groups in C21 steroids and a reduction in activity of 14 and 5–6%, respectively, for 5-pregnene and 5β-pregnanes compared to 4-pregnenes. Corticosteroids, testosterone and 17β-oestradiol were ineffective. Folliculated oocytes stimulated by pituitary homogenate produced 17,20β,21-P from endogenous substrates in amounts one order of magnitude higher than 17,20β-P. These results strongly support the hypothesis that 17,20β,21-P is the likely MIS in this species. |
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Keywords: | oocyte maturation maturation-inducing hormone 17 20β 21-trihydroxy-4-pregnen-3-one Lusitanian toadfish Halobatrachus didactylus |
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