Presence of urokinase plasminogen activator and plasminogen activator inhibitor-1 messenger ribonucleic acids in rat endometrium during decidualization in vivo

Rat endometrial stromal cells undergoing decidualization in vitro secrete urokinase-type plasminogen activator (uPA), and this secretion is regulated by prostaglandin E₂. The present study was undertaken to determine whether uPA and plasminogen activator inhibitor-1 (PAI-1) mRNAs are expressed in vivo in the decidua of pregnant rats and in the deciduoma of 'pseudopregnant' rats. Total RNA was prepared from nondecidualized and decidualized endometrial tissues at various stages of early pregnancy and examined by Northern blot analysis using specific cDNA probes for rat uPA and PAI-1. There was little uPA mRNA in the endometrium during the first 5 days of pregnancy (Day 1 = the presence of sperm in the vagina). A high level of uPA mRNA was detected on Day 7, and it declined thereafter. There was a gradual increase in PAI-1 mRNA in the decidua from Day 7 of pregnancy, reaching a peak level on Day 15 when the decidua was transformed into the maternal placenta. (RNA was not analyzed beyond Day 15 of pregnancy in this study.) In situ hybridization studies verified that uPA mRNA was present in the decidua adjacent to the implanting embryo on Day 7. Plasminogen activator inhibitor-1 mRNA was scattered in the decidualized endometrium, but greater amounts of PAI-1 mRNA were found in the fetal tissue on Day 10 of pregnancy. Northern blot analysis of RNA from the deciduoma produced in ovariectomized, steroid-treated rats by intrauterine injection of oil demonstrated a similar temporal pattern of expression of uPA mRNA; i.e., the level of uPA mRNA was highest on Day 7 and decreased thereafter. The level of PAI-1 mRNA in deciduoma was not detectable by Northern blot technique during the first 10 days of pseudopregnancy. These findings confirm that uPA mRNA is present in vivo in rat decidual cells, independent of the presence of a conceptus. By contrast, the level of PAI-1 mRNA in the uterus is probably influenced by the presence of the conceptus.