Arachidonic acid as a stimulatory mediator of luteinizing hormone-releasing hormone action in the rat ovary.

The present study further examined the role of arachidonic acid (AA) in the action of LHRH on ovarian steroidogenesis. Rat granulosa cells were incubated with LHRH and/or AA in the presence of FSH for 24 h. As expected, the presence of LHRH markedly attenuated the FSH-induced progesterone (P) production. AA by itself did not affect the magnitude of P production induced by FSH. However, when AA (10(-5) M) was added during the last 6 h to the cultures containing LHRH and FSH, AA partially reversed the inhibitory action of LHRH (by 42%). Likewise, addition of AA partially antagonized the inhibitory effect of 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-9) M) on FSH-induced P production (by 71%). Pretreatment of granulosa cells with TPA or LHRH without FSH for 18 h did not alter the stimulatory effect of AA on P formation during the subsequent 6-h culture period. In other experiments granulosa cells were incubated for 5 h in the absence of FSH. Treatment with AA, TPA, or LHRH alone caused significant increase in P production. Combined treatment with AA and LHRH or AA plus TPA showed additive effects on P formation. By contrast, AA failed to potentiate the effect of LHRH or TPA on 20 alpha-hydroxyprogesterone accumulation. Although AA by itself slightly stimulated 20 alpha-hydroxyprogesterone production, the magnitude was much less than that induced by TPA or LHRH. When 25-hydroxycholesterol was present in the incubation medium, P production was significantly increased. In the presence of 25-hydroxycholesterol, AA further increased P formation, but did not enhance the stimulatory actions of LHRH or TPA in this regard. Taken together, these results further support the hypothesis that AA (or its metabolites) play a stimulatory role in the direct action of LHRH on ovarian steroidogenesis.