Plasma levels of beta-endorphin and ACTH during labor and immediate puerperium.

We measured concentrations of beta-endorphin (beta-EP) and adrenocorticotropic hormone (ACTH) in maternal peripheral plasma during dilation, the expulsive period and immediate puerperium, and in the umbilical vein. Plasma levels of both peptides increased markedly and were directly correlated during labor, and decreased 24 h after birth; they were no longer correlated during immediate puerperium. In the umbilical vein, beta-EP and ACTH were also directly correlated. Moreover, the concentration of each of the two peptides in maternal plasma during the expulsive period was correlated with the corresponding concentration in umbilical vein. We discuss the importance of placental corticotropin-releasing factor in the regulation of maternal and fetal stress.