Effects of epidural anesthesia during labor on maternal plasma beta-endorphin levels.

Plasma beta-endorphin (beta-EP) was measured in 48 women. Twenty-three were in labor. In 13 of the 23 patients in labor, beta-EP was determined prior to and after complete onset of epidural anesthesia, and in 10 women, who served as controls, prior to and after injection of saline into the epidural space as part of the loss of resistance technique, but before injection of the local anesthetic. Venous blood also was obtained for plasma beta-EP determinations from 10 healthy non-pregnant women and from 15 patients scheduled for elective repeat cesarean section and who were not in labor. Human beta-EP was determined by radioimmunoassay following silicic acid extraction of plasma samples and separation of the beta-EP fraction by gel chromatography. In the 10 non-pregnant volunteers, plasma beta-EP averaged 11.3 +/- 1.5 fmol/ml (mean +/- SE) as compared with 43.7 +/- 6.5 fmol/ml observed in the 15 women with term pregnancies who were not in labor (P less than 0.005). In the 13 patients in labor who underwent epidural anesthesia, plasma beta-EP concentrations decreased (P less than 0.005) from 54.5 +/- 9.0 to 28.2 +/- 3.5 fmol/ml, whereas there was no significant change in plasma beta-EP levels in the 10 controls who averaged 64 +/- 20.5 and 55.8 +/- 13.6 fmol/ml prior to and following saline injection. These data confirm that plasma beta-EP levels are significantly higher in women with term pregnancies in labor than in non-pregnant women and also demonstrate that epidural anesthesia during labor is accompanied by a significant decrease in maternal plasma beta-EP concentrations.