Immunohistochemical localization of ECE-1 in the human placenta.

Over the last several years, endothelin (ET-1) has emerged as an important mediator in the pathogenesis of pre-eclampsia and preterm labour, as well as in the normal function of gestational tissues. While the distribution of ET and its binding sites in the human placenta have been well studied, much less has so far been reported about the distribution of placental ET-1 processing enzymes. By immunohistochemical analysis and immunofluorescence, endothelin-converting enzyme-1 (ECE-1), the enzyme that synthesizes ET-1, is localized to five distinct cell populations in the human placenta: (1) the endothelial cells lining the maternal basal plate blood vessels, (2) the intermediate trophoblasts, (3) the endothelial cells lining the chorionic villous blood vessels, (4) the chorionic villous stromal cells and (5) the chorionic villous trophoblasts. The localization of ECE-1 corresponds with the previously reported distribution of ET-1 in the human placenta and is in accordance with the function of this enzyme in regulating vascular tone through synthesis of ET-1. The abundance of ECE-1 in the basal plate is consistent with a second possible function of this enzyme in affecting uterine contractions. ECE-1 may serve as a target for prognosis and therapy in states of pathologically altered vascular tone and/or altered myometrial smooth muscle tone in gestation.