Synthesis of endothelin-1 in rat uterus during pregnancy.

Endothelin is a potent vasoconstrictive peptide first isolated from the supernatant of cultured porcine aortic endothelial cells. The purpose of this study was to determine the source of endothelin-1 (ET-1) production in rat uterus during pregnancy and to clarify its role in normal pregnancy. ET-1, as recognized by immunohistochemistry, was weakly expressed only in endometrial glandular cells in nonpregnant rats but was intensely expressed in both glandular and myometrial cells in the early postpartum period. In situ hybridization confirmed the localization of prepro-ET-1 mRNA in the cytoplasm of endometrial glandular and myometrial cells but not in stromal cells or in smooth muscle cells of blood vessels. Northern blot analysis detected prepro-ET-1 mRNA in myometrial tissue from pregnant but not nonpregnant rats. In particular, the expression of prepro-ET-1 mRNA was strongest in the early postpartum period compared with the various stages of pregnancy. These results indicate that, in addition to endothelial cells and endometrial glandular cells, myometrial cells also produce ET-1 and its production significantly increases in the early postpartum period. Therefore, ET-1 may play a pivotal role in controlling bleeding from the placental bed through myometrial contraction.