Objective: To examine endothelin 1 (ET-1) in normal pregnancies and those complicated by severe intrauterine growth retardation (IUGR) with normal or increased fetoplacental vascular resistance as assessed by umbilical artery Doppler flow velocimetry.
Methods: Endothelin 1 concentrations were measured by radioimmunoassay in fetal umbilical arterial and venous and maternal venous plasma, and vascular ET-1 receptors were quantified by radioligand binding methods in placental primary and secondary stem villous vessels.
Results: Fetal and maternal ET-1 concentrations were similar in normal pregnancy (10-15 pmol/L) and were not influenced by mode of delivery (vaginal versus cesarean). Fetal levels were identical to control values in the growth-retarded fetuses with normal umbilical artery flow, but were markedly elevated (above 50 pmol/L) in two cases with increased fetoplacental vascular resistance. The corresponding maternal levels also appeared elevated, but to a lesser extent. Endothelin receptors were identified in placental vascular tissue. No differences in receptor-binding characteristics were observed between the groups.
Conclusion: The increased fetoplacental vascular resistance present in a proportion of pregnancies complicated by severe IUGR may be associated with elevated fetal plasma ET-1 concentrations, but with no apparent change in vascular sensitivity to the peptide.