Endothelin-1 in smooth muscle cells and mast cells of mouse uterus after parturition

To elucidate the physiological importance of endothelin-1 (ET-1) in mouse uterus, we investigated quantitative changes in ET-1 mRNA levels in the uterus during the estrous cycle, pregnancy and post-parturient period by use of the real-time PCR technique and we examined the cellular distribution of the ET-1 peptide by use of immunohistochemical techniques. Low and constant mRNA levels were observed in the uterus from cyclic or pregnant mice. However, a significant increase in mRNA levels was found immediately after parturition (day 0 postpartum) which then decreased gradually to a basal level at day 14 postpartum. Discernible immunopositivity was found in myometrial cells as well as in endometrial epithelial cells in the post-parturient uterus. Myometrial cells showed the strongest staining at day 0 postpartum, and some large cells in the myometrial layers, intensely positive for ET-1, were characterized as mast cells. These findings suggest the possibility that in mouse uterus ET-1 may play a role in recovery from the uterine changes caused by pregnancy and parturition.