In vitro effects of 2-hydroxyestradiol-17β on ovarian follicular steroid secretion in the catfish Heteropneustes fossilis and identification of the receptor and signaling mechanisms

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Ovarian pieces containing postvitellogenic follicles were incubated in vitro with different concentrations of the catecholestrogen 2-hydroxyestradiol-17β (2-OHE 2) to evaluate its effects on steroid production and germinal vesicle breakdown (GVBD) in the catfish Heteropneustes fossilis. The incubation with 2-OHE 2 induced a shift in steroidogenic pattern: the C 19 and C 18 steroids testosterone (T) and estradiol-17β (E 2), respectively were significantly decreased with a concomitant significant increase in the C 21 steroids progesterone (P 4), 17-hydroxyprogesterone (17-OHP), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-DP), 17,20α-dihydroxy-4-pregnen-3-one (17,20α-DP) and cortisol (F). Concomitantly, the catecholestrogen induced dose-dependently GVBD response, the first sign of meiosis resumption. The co- and pre-incubations of the ovarian pieces with 2-OHE 2, and adrenergic (phentolamine, α-blocker and propranolol, β-blocker) or estrogen (tamoxifen) receptor blockers resulted in inhibition of the stimulatory effect of the catecholestrogen on C 21 steroids and reversed the inhibition of testosterone and E 2. The α-blocker was more effective than the β-blocker. Our results suggest that 2-OHE 2 appears to employ both adrenergic (α-type) and estrogen receptor mechanisms in mediating the effects. The co- or pre-incubation of ovarian pieces with IBMX (a cAMP elevating drug), H89 (a protein kinase A inhibitor), and PD098059 (a MAP kinase kinase inhibitor) significantly inhibited the stimulatory effect of 2-OHE 2 on the C 21 steroids. The effect of chelerythrine (a protein kinase C inhibitor), on the other hand, varied with the incubation condition. In the co-incubation, the steroids showed varied effects: 17,20β-DP, testosterone and E 2 were elevated, and P 4 and 17-OHP were decreased. In the pre-incubation set up, all the steroids were inhibited except E 2. The inhibition by the blockers was higher in the pre-incubation groups. Taken together, the data suggest the involvement cAMP–protein kinase A, protein kinase C and MAP kinase pathways in the modulation of the steroidogenic activity.