Maternal and fetal levels of a novel polypeptide, endothelin: evidence for release during pregnancy and delivery.

The occurrence of endothelin (ET), a recently discovered polypeptide with potent vasoconstrictor properties, was studied in maternal and umbilical blood and amniotic fluid. The level of ET-like immunoreactivity (ET-LI) in maternal plasma was in most cases below the detection limit of the radioimunoassay, i.e. less than 2 pmol/l. The median concentration of ET-LI in the umbilical artery and vein before the initiation of breathing was 14.9 and 10.9 pmol/l, respectively. When sampling was performed after fetal breathing had begun, the arterial concentration increased to 93.7 pmol/l. Labor was not associated with increased concentrations of ET-LI, however, since neonates delivered by elective cesarean section had similar ET-LI in blood and amniotic fluid as after vaginal delivery. An approximately fivefold increase in the amniotic fluid ET-LI was seen at term as compared to early mid-trimester values. Reversed phase HPLC characterization revealed that the observed ET-LI mainly corresponded to ET-1. It is suggested that ET-1 may contribute to the fetal hemodynamic changes, e.g., closure of the umbilical vessels occurring at delivery.