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17a,20ß,21-trihydroxy-4-pregnen-3-one: the probable maturation-inducing steroid of the lusitanian toadfish

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17,20 ,21-Trihydroxy-4-pregnen-3-one (17,20 ,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. 17,20 -Dihydroxy-4-pregnen-3-one (17,20 -P) and 17,20 ,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 20 -hydroxyl groups in C21 steroids and a reduction in activity of 14 and 5–6%, respectively, for 5-pregnene and 5 -pregnanes compared to 4-pregnenes. Corticosteroids, testosterone and 17 -oestradiol were ineffective. Folliculated oocytes stimulated by pituitary homogenate produced 17,20 ,21-P from endogenous substrates in amounts one order of magnitude higher than 17,20 -P. These results strongly support the hypothesis that 17,20 ,21-P is the likely MIS in this species.



Oocyte maturation Halobatrachus didactylus Lusitanian toadfish 17,20 ,21-trihydroxy-4-pregnen-3-one Maturation-inducing hormone


Modesto, T; Adelino V. M. Canário. 17a,20ß,21-Trihydroxy-4-pregnen-3-one: the probable maturation-inducing steroid of the Lusitanian toadfish, Journal of Fish Biology, 60, 3, 637-648, 2002.

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The Fisheries Society of the British Isles