Estrogen-2/4-hydroxylase activity is stimulated during germinal vesicle breakdown induced by hCG, IGF-1, GH and insulin in the catfish Heteropneustes fossilis.

Estrogen-2/4-hydroxylase (EH) activity was measured radiometrically in ovaries of catfish injected with hCG intraperitoneally and in postvitellogenic follicles incubated with different concentrations of hCG, catfish (Clarias batrachus) growth hormone (GH), bovine insulin or recombinant human insulin-like growth factor-I (rhIGF-I). The change in enzyme activity was correlated with germinal vesicle breakdown (GVBD), an index of oocyte maturation. A single intraperitoneal injection of hCG (100 IU/fish) stimulated EH activity both at 8 and 16 h prior to stripping of eggs. The activity decreased significantly at 24 h, following ovulation. The follicles incubated with hCG, rhIGF-I, insulin or GH elicited biphasic effects on EH activity. rhIGF-I, insulin and GH increased enzyme activity at the lower or median concentrations. hCG and rhIGF-I stimulated EH activity higher than GH or insulin. All the hormones elicited a dose-dependent increase in GVBD, the effect was greater with rhIGF-I (100 nM) and hCG (5.0 IU/ml). The significance of changes in EH activity (E2 hydroxylation) and GVBD were discussed.