LIPID HYDROPEROXIDES EVOKE ANTIGONADOTROPIC AND ANTISTEROIDOGENIC ACTIVITY IN RAT LUTEAL CELLS

At functional luteolysis, the rat corpus luteum generates hydrogen per oxide (H2O2), which is known to rapidly inhibit gonadotropin-sensitive cAMP and progesterone production in isolated luteal cells. Lipid pero xides also increase markedly in the rat corpus luteum with the onset o f functional luteolysis, and H2O2 is a potent inducer of lipid peroxid ation. However, the actions of lipid peroxides on cell function are un known. The objective of this study was to investigate the impact of ty pical lipid peroxides, cumene hydroperoxide (CuOOH) and 15(S)-hydroper oxyeicosatetraenoic acid, on rat luteal cells. CuOOH inhibited both LH -sensitive cAMP accumulation (ED(50), 25 mu M) and progesterone produc tion (ED(50), 20 mu M). 15(S)-hydroperoxyeicosatetraenoic acid also do se dependently inhibited steroidogenesis. A significant reduction of L H-stimulated progesterone production was evident within 5 min of treat ment with CuOOH, whereas inhibition of cAMP accumulation was not evide nt until 60 min. 8-Bromo-cAMP and 22-hydroxycholesterol caused partial and complete reversal of CuOOH-inhibited progesterone secretion, resp ectively. Preincubation of cells with o-phenanthroline completely reve rsed the inhibitory effect of CuOOH on cAMP accumulation and partially reversed its effect on progesterone production. Incorporation of radi olabeled amino acids into luteal proteins was significantly inhibited by CuOOH (25 mu M) within 2 min of treatment and was reduced to 40 +/- 14% of control levels at 60 min. CuOOH (25 mu M) maximally stimulated PGE(2) production within 30 min of treatment (180 +/- 30% of control) , a response that was completely blocked by aristolochic acid (100 mu M), a phospholipase-Aa inhibitor, and indomethacin (1 mu g/ml), a pros taglandin (PG) synthesis inhibitor. The present results suggest that t he acute inhibitory action of lipid peroxides on LH-stimulated progest erone production occurs down-stream of cAMP synthesis and appears to b e due to impaired cholesterol utilization for steroidogenesis, possibl y through inhibition of protein synthesis. The stimulation of PGE(2) p roduction by CuOOH appears to involve the activation of phospholipase- az, which is a rate-limiting step in PG synthesis. Lipid peroxides as well as H2O2 may serve as mediators of functional luteolysis.