INHIBITION OF PROTEIN-SYNTHESIS AND HORMONE-SENSITIVE STEROIDOGENESISIN RESPONSE TO HYDROGEN-PEROXIDE IN RAT LUTEAL CELLS

Hydrogen peroxide (H2O2) is generated in the corpus luteum at function al luteal regression and produces rapid antigonadotropic effects in ra t luteal cells. However, the mechanism by which peroxide interrupts LH - and cAMP-sensitive progesterone synthesis is unknown. The post-cAMP site of H2O2 action is due to the reduced cholesterol availability in mitochondria, and this process is well known to be dependent on protei n synthesis. Therefore, we examined whether H2O2 may interfere with pr otein and RNA synthesis, and whether such responses may be associated with inhibition of steroidogenesis. Incorporation of radiolabelled ami no acids into luteal proteins was inhibited in response to H2O2 in a t ime- and dose-dependent manner, and these doses are similar to those t hat inhibit progesterone synthesis, shown earlier in the identical par adigm. The inhibitory effect of H2O2 On amino acid incorporation was n ot due to increased protein degradation, impaired transport of amino a cids, or depletion of cellular ATP levels. H2O2 also inhibited RNA syn thesis, increased RNA degradation, and impaired the efficiency of mRNA as a translation template. The time course for the inhibitory effect of H2O2 On protein and RNA synthesis was very rapid and coincident wit h inhibition of steroidogenesis. Inhibition of protein and RNA synthes is and steroidogenesis were reversed by preincubation of cells with th e cell-permeable metal chelator o-phenanthroline, which implicates met al-dependent radical generation as the probable mediator of these acti ons of H2O2. We conclude that the target of the post-cAMP site of pero xide-induced inhibition of cAMP-dependent steroidogenesis is the inhib ition of rapidly inducible proteins that are known to mediate transloc ation of cholesterol within mitochondria, where it is used as a substr ate for pregnenolone synthesis.