Elevated plasma beta-endorphin levels in pregnant women and their neonates.

Using radioimmunoassay technique β-endorphin levels were measured in the plasma of women undergoing labour and partirition and in the plasma of their neonates. The level of immunoreactive β-endorphin in the plasma of women undergoing labour was found to be significantly elevated (mean values: 38–135 fmoles/ml) above the levels found in non-pregnant women (mean values: 5–10 fmoles/ml). After birth, the level of β-endorphin-like immunoreactivity in maternal venous plasma was significantly higher than that in the umbilical vein and artery plasma of the new-borns, but there was no arterio-venous difference in the neonatal plasma. Since the antiserum used displayed the same avidity for human β-endorphin and β-lipotropin chromatographic separation of the immunoreactive components was performed by gelfiltration. Both peptides were found in the plasma of non-pregnant women, in maternal plasma and in the plasma of the neonates. In addition, high amounts of both peptides were found in the fetal pituitary gland showing that the fetus can probably produce its own peptides.