Visualization of 125I-endothelin-1 binding sites in human placenta and umbilical vessels.

Endothelin-1 (ET-1) has potent vasoconstrictor effects and thus may be involved in regulating fetoplacental vascular resistance. By using quantitative in vitro autoradiography, the 125I-ET-1 binding sites in human placentas and umbilical vessels were localized and quantified. A high density of specific 125I-ET-1 binding sites was found in the placental villi and vessels. In the media of umbilical vessels, affinity for the peptide was higher in arteries than in veins. In all structures, 125I-ET-1 binding was inhibited with unlabeled ET-1 in the picomolar range. Unrelated peptides such as oxytocin or atrial natriuretic peptide failed to compete for 125I-ET-1 binding. The localization of binding sites points to a regulation of hemodynamic functions of ET-1 on the fetal side of the placental circulation and supports evidence regarding ET-1 as a paracrine-acting vasoconstrictor.