Role of prostaglandin in the control of ovulation in the Japanese eel Anguilla japonica

The in vitro effects of 17,20beta-dihydroxy-4-pregnen-3-one (DHP) and prostaglandins (PGE(1), PGE(2), PGF(1alpha), PGF(2alpha)) on ovulation in the Japanese eel Anguilla japonica were examined. Oocytes with follicle layers at the migratory nucleus stage (approximately 850-900 mum diameter) were removed using a polyethylene cannula from artificially matured fish. At concentrations of 10 and 100 ng/mL, DHP was found to induce both germinal vesicle breakdown and ovulation. The prostaglandins, except for PGE(1), effectively induced ovulation of previously matured oocytes by DHP treatment in vitro. Prostaglandin F-2alpha was the most effective. A significant increase in ovulation rate was observed even at a concentration of 0.01 mug/mL PGF(2alpha). Indomethacin blocked the in vitro ovulation induced by DHP and addition of PGF(2alpha) reversed indomethacin-blocked ovulation. Actinomycin D and cycloheximide blocked DHP-induced ovulation and PGF(2alpha) reversed the effects of both inhibitors. These results indicate that DHP induces ovulation through endogenous prostaglandin synthesis in the follicle layers of the Japanese eel.