MECHANISMS OF ACTION OF FREE ARACHIDONIC-ACID ON OVARIAN-STEROID PRODUCTION IN THE GOLDFISH

This study explores the mechanisms by which free arachidonic acid (AA) affects ovarian steroidogenesis by full-grown prematurational follicl es of the goldfish in vitro. AA (6-400 mu M) stimulated testosterone p roduction and this action was mediated by prostaglandin E(2) (PGE(2)). The steroidogenic actions of AA and the corresponding increase in the production of PGE(2) were blocked by inhibitors of the cyclooxygenase pathway (indomethacin, ETYA). Exogenous PGE(2) (20-2000 ng/ml) also s timulated steroid production. In the presence of human chorionic gonad otropin (hCG), AA had differential effects. AA potentiated the steroid ogenic actions of low dosages of hCG (0.1 IU/ml), while with maximal g onadotropin (1-10 IU/ml) stimulation a high concentration of AA (400 m u M) attenuated steroid production in spite of elevated PGE(2) concent rations. HCG did not induce PGE(2) synthesis, nor did it affect the PG E(2) production obtained with AA-treated follicles. The steroidogenic induction by AA via PGE(2) was mediated in part by Ca2+ since the calc ium channel blocker nifedipine (25 mu M) inhibited stimulated steroid production by both AA and PGE(2). The conversion of AA to PGE(2) does not require Ca2+ since PGE(2) production by AA-treated follicles was n ot affected by nifedipine. However, treatment with the calcium ionopho re A23187 (1 mu M) potentiated the stimulatory actions of AA on steroi d and prostaglandin production. The phosphodiesterase inhibitor 3-isob utyl-1-methylxanthine (1 mM) potentiated the stimulatory actions of AA on testosterone production but had no effect on the conversion of AA to PGE(2). The steroidogenic actions of AA and PGE(2) involve both tra nscription and translation since stimulated steroidogenesis was inhibi ted by actinomycin D and cycloheximide (1-10 mu g/ ml). The conversion of AA to PGE(2) was also blocked by these inhibitors. These results u nderscore the importance of AA and PGE(2) in the regulation of ovarian steroidogenesis in the goldfish. (C) 1996 Academic Press, Inc.