Effects of steroid hormones on in vitro oocyte maturation in white sturgeon (Acipenser transmontanus)

The in vitro effects of several steroids on the maturation of intact white sturgeon (Acipenser transmontanus) ovarian follicles were investigated. At the highest concentration (1024 ng ml−1 for the C21 steroids and 1139 ng ml−1 for the C19 steroids), all of the C21 steroids tested, progesterone (P4), 17α-hydroxyprogesterone (17OHP), 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P), 17α,(20β,21-trihydroxy-4-pregnen-3-one 20β-S), 11-deoxycortisol (S) and cortisol (F), as well as testosterone (T) induced germinal vesicle breakdown (GVBD) at 14 and 22 h. At 6 h, only P4 and 17,20β-P induced maturation at the highest concentration (1024 ng ml−1). At 14 and 22 h, 11-deoxycortisol was the most potent steroid inducer of GVBD followed by P4, 17OHP, 17,20β-P, and 20β-S. The steroid 11β-hydroxytestosterone (11βOHT) was completely ineffective at all concentrations and exposure times. The C21 steroids induced oocyte maturation at concentrations ranging from 4 to 1024 ng ml−1, whereas T induced GVBD at 225 to 1139 ng ml−1. Calculation of the mean effective concentration that induced 50% GVBD (EC50) from the 22 h incubations revealed the following order of potencies: S > P4 > 17OHP > 17,20β-P > 20β-S >> F > T. These bioassay results, together with previous findings on the endogenous production of steroids by ovarian follicles from gonadotropin-primed females, indicate that more than one steroid has a biological role in the resumption of meiosis in sturgeon oocytes and provides empirical evidence for P4, 17OHP, S, 20β-S, and 17,20β-P as maturation-inducing steroids in white sturgeon.