Plasma β-Endorphin-Like Immunoreactivity During Pregnancy, Parturition, Puerperium and in Newborn

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Abstract
Mean .beta.-endorphin-like immunoreactivity in the plasma of 10 normal women in the 10th month of pregnancy was 144.3 .+-. 7.5 ng/l. During labor in 7 women its immunoreactivity was increased and peaked at the time of vaginal delivery (1162 .+-. 69 ng/l). Two hours after delivery, .beta.-endorphin-like immunoreactivity was significantly decreased (297 .+-. 39 ng/l) and after 4 to 5 days was 155 .+-. 33 ng/l. Beta-endorphin-like immunoreactivity in the cord plasma (523 .+-. 30 ng/l) was significntly lower than in the mother at the time of vaginal delivery and in venous blood of newborns 24 hours post partum was 156 .+-. 11 ng/l. The correlation between .beta.-endorphin-like immunoreactivity in the mother and the cord blood plasma was not determined. At the time of the fetal hypoxia, .beta.-endorphin-like immunoreactivity in the cord blood plasma was increased (2741 ng/1). We conclude that immunoreactive .beta.-endorphin influences a stress reaction in the mother and fetus at the time of labor. During intra-uterine life the fetus probably produces its own immunoreactive-like .beta.-endorphin independently of the maternal production of this peptide.