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 follicles of the goldfish in vitro. AA (6-400 mu M) stimulated testosterone production 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 stimulated steroid production. In the presence of human chorionic gonadotropin (hCG), AA had differential effects. AA potentiated the steroidogenic actions of low dosages of hCG (0.1 IU/ml), while with maximal gonadotropin (1-10 IU/ml) stimulation a high concentration of AA (400 mu M) attenuated steroid production in spite of elevated PGE(2) concentrations. HCG did not induce PGE(2) synthesis, nor did it affect the PGE(2) production obtained with AA-treated follicles. The steroidogenic induction by AA via PGE(2) was mediated in part by Ca2+ since the calcium 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 not affected by nifedipine. However, treatment with the calcium ionophore A23187 (1 mu M) potentiated the stimulatory actions of AA on steroid and prostaglandin production. The phosphodiesterase inhibitor 3-isobutyl-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 transcription and translation since stimulated steroidogenesis was inhibited 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 underscore the importance of AA and PGE(2) in the regulation of ovarian steroidogenesis in the goldfish. (C) 1996 Academic Press, Inc.