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

Ovarian pieces containing postvitellogenic follicles were incubated in vitro with different concentrations of the catecholestrogen 2-hydroxyestradiol-17β (2-OHE2) to evaluate its effects on steroid production and germinal vesicle breakdown (GVBD) in the catfish Heteropneustes fossilis. The incubation with 2-OHE2 induced a shift in steroidogenic pattern: the C19 and C18 steroids testosterone (T) and estradiol-17β (E2), respectively were significantly decreased with a concomitant significant increase in the C21 steroids progesterone (P4), 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-OHE2, 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 C21 steroids and reversed the inhibition of testosterone and E2. The α-blocker was more effective than the β-blocker. Our results suggest that 2-OHE2 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-OHE2 on the C21 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 E2 were elevated, and P4 and 17-OHP were decreased. In the pre-incubation set up, all the steroids were inhibited except E2. 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.

► 2-Hydroxyestradiol-17β induces final oocyte maturation in catfish.
► It involves stimulation of C-21, and inhibition of C-19 and C-18 steroids.
► The effect is mediated through both estrogen and adrenergic receptors.
► MAP kinase, protein kinase C and cAMP–PKA signaling pathways are involved.