Cellular localization of tissue factor and prothrombin in the estrogen-treated immature rat uterus

The immediate early responses of the immature rat uterus to estradiol include increases in tissue factor and prothrombin, two proteins of the coagulation cascade. Both attain maximum activity within 3 h after the administration of estradiol and return to control levels after 12-18 h. The presence of the two proteins allows the generation of thrombin (a known growth factor for fibroblasts) in the uterus at the time when uterine growth begins. To further our hypothesis that thrombin is an estrogen-regulated uterine growth factor, we used immunohistochemistry, Western blotting, and coagulation assays to localize the cell types in which these proteins are increased by estradiol. Tissue factor is increased in both the stromal and the epithelial cells. Increased prothrombin is localized primarily along the basement membrane that separates the epithelial and stromal layers and also at the luminal surface of the epithelium.