Plasma levels of immunoreactive beta-endorphin and adrenocorticotropic hormone during labor and delivery.

beta-endorphin and adrenocorticotropic hormone (ACTH) are derived from the same precursor protein, and the plasma levels of beta-endorphin and ACTH are thought to be representative of the pituitary secretion of these peptides. Simultaneous measurements of immunoreactive beta-endorphin and ACTH were done on plasma samples from pregnant women at term and found to be normal, but a significant increase was observed during the stress of labor. Simultaneous measurement of immunoreactive beta-endorphin and ACTH in the umbilical vein at time of vaginal delivery demonstrated elevated levels of both peptides. The newborn also demonstrated an increased ratio of beta-endorphin to ACTH, of which the role is uncertain at present.