PROGESTERONE INHIBITS SUPEROXIDE RADICAL PRODUCTION BY MONONUCLEAR PHAGOCYTES IN PSEUDOPREGNANT RATS

This study investigated the changes in superoxide radical production b y mononuclear phagocytes in the corpus luteum (CL) during pseudopregna ncy in rats. Activity of superoxide radical production was determined by the conversion of nitro blue tetrazolium (NBT) to blue formazan dep osit. Rats received 10 mg NBT via the abdominal aorta on day 3, 7, or 13 of pseudopregnancy and were autopsied 1 min later to prepare the hi stological sections. The cells with blue formazan deposits (NBT-positi ve cells) in the CL were scarce on days 3 and 7 of pseudopregnancy and significantly increased on day 13 of pseudopregnancy. On the other ha nd, simultaneous administration of 100 mu g phorbol 12-myristate 13-ac etate, which activates mononuclear phagocytes to produce superoxide ra dical, significantly increased the numbers of NBT-positive cells in th e CL on day 7 of pseudopregnancy, but not in the CL on day 3 or 13 of pseudopregnancy. To study the possibility that superoxide radical prod uction by mononuclear phagocytes is inhibited by progesterone on day 7 of pseudopregnancy, peritoneal mononuclear phagocytes prepared on day 7 or 13 of pseudopregnancy were preincubated with 10, 50, or 100 ng/m l progesterone for 6 h and then stimulated with phorbol 12-myristate 1 3-acetate. Superoxide radical production was measured by the cytochrom e c reduction method. One hundred nanograms per ml progesterone signif icantly inhibited superoxide radical production by mononuclear phagocy tes, and this inhibitory effect of progesterone was significantly bloc ked by the simultaneous addition of RU486 (10(-7) M). These results su ggested that progesterone inhibited superoxide radical production by t he mononuclear phagocytes in the CL during midpseudopregnancy in rats.