Possible role for arachidonic acid in the control of steroidogenesis in hen theca

Studies were conducted to evaluate if arachidonic acid (C20:4) could function as a second messenger within theca cells from the second largest preovulatory (F₂) follicle from the ovary of the domestic hen. Arachidonic acid stimulated basal progesterone and androstenedione production, but inhibited LH-induced androstenedione production. The stimulatory effects of arachidonic acid were not altered by either cyclooxygenase or lipoxygenase pathway inhibitors (indomethacin and nordihydroguaiaretic acid, respectively), but were blocked by agents that prevented mobilization and/or efflux of calcium (TMB-8 and verapamil). The inhibitory effects of arachidonic acid on LH-stimulated steroidogenesis were determined to occur both prior and subsequent to cAMP formation. Fifty and 100 μM arachidonic acid attenuated LH- (10 ng) and forskolin- (0.2 μM) induced cAMP levels, and decreased androstenedione and estradiol production following treatment with 8-bromo-cAMP. Phospholipase A₂ (PLA₂) and the calcium ionophore, A23187, stimulated the release of ³H from theca cells prelabeled with [³H]arachidonic acid, and both PLA₂ and the closely related fatty acid, eicosatrienoic acid (C20:3), could replicate the inhibitory effects of arachidonic acid on LH-stimulated androstenedione production. Finally, neither indomethacin nor nordihydroguaiaretic acid blocked the inhibitory effects of arachidonic acid on LH-promoted androstenedione production. We conclude that arachidonic acid can be released within theca cells in response to physiologic (PLA₂) and pharmacologic agents (A23187), and accordingly, that it may act directly as a second messenger to modulate both basal and LH-stimulated steroid production.