Progesterone regulation of estradiol-induced rat uterine secretory protein, complement C3

Previously, using DNA sequencing, Northern and Southern analysis, and immunohistochemical data, we identified an estrogen-stimulated secretory protein as the third component of complement (C3). In this study, we demonstrate that progesterone modulated the estradiol regulation of C3 in immature rats as well as during the normal reproductive cycle. C3 was most abundant during estrus and reached its lowest concentration in diestrus. Immunoprecipitations reveal that progesterone prevented the estradiol-stimulated increase in radiolabeled C3 both in the media and tissue. The mechanism for the progesterone inhibition of estrogen-stimulated C3 appeared to be at the level of transcription or possibly mRNA stability since progesterone blocked the estradiol-stimulated increase in C3 mRNA.