The effect of four C21-steroids on oocyte maturation in Siberian sturgeon (<Emphasis Type="Italic">Acipenser baeri</Emphasis> Brandt)

The effect of four C21-steroids, progesterone (P₄), 17,20β-dihydroxy-4-pregnen-3-one (17,20βP), 17,20β,21-trihydroxy-4-pregnen-3-one (20βS) and 11-desoxycortisol (S), on in vitro oocyte maturation in Siberian sturgeon (Acipenser baeri Brandt) females was demonstrated using short-term (5 and 30 min) exposures of ovarian follicles to steroid solutions followed by incubation in steroid-free medium. The study aimed to find out which of the four candidates for a maturationinducing steroid (P₄, 17,20βP, 20βS or S) induces a fastest germinal vesicle breakdown (GVBD) in oocytes of Siberian sturgeon. Dissolution of the oocyte nucleus or GVBD was taken as a criterion of oocyte maturation. Dose-response profiles of hormone activities as well as effects of the hormones under short-term exposures of follicles to their equal doses were compared. P₄ was found to be a most active GVBD inducer compared to other C21-steroids, S was the second in its activity, whereas 17,20βP and 20βS were less efficient. A comparison of the present and previously obtained data on the dynamics of C21-steroids in vivo and their effect on ovarian follicles in vitro indicates an important role of the above hormones, particularly P₄ and 20βS, in the regulation of the final stage of oocyte maturation in sturgeons.