Effects of Epidural Anesthesia during Labor on Maternal Plasma Beta-Endorphin Levels

Abstract

Plasma .beta.-endorphin (.beta.-EP), was measured in 48 women. A total of 23 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 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) as compared with 43.7 .+-. 6.5 fmol/ml observed in the 15 women with term pregnancies who were not in labor (P < 0.05). In the 13 patients in labor who underwent epidural anesthesia, plasma .beta.-EP concentrations decreased (P < 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. Evidently 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.