Humoral endorphin in human body fluids during pregnancy

The presence of an enkephalin-like substance ('humoral endorphin') in human maternal and cord blood, as well as in amniotic fluid, has been demonstrated in this study. Utilizing antibodies to leucine-enkephalin, it was found that the level of this substance in maternal and in cord blood remained stable during pregnancy whereas the concentration in amniotic fluid was significantly higher at mid-trimester than during labor at term.