Effect of intrathecal morphine during labor on maternal plasma beta-endorphin levels

Plasma beta-endorphin was measured in 16 patients in labor prior to and after complete onset of analgesia with 1 mg of morphine administered intrathecally. Human beta-endorphin levels were determined by radioimmunoassay following silicic acid extraction of plasma samples and separation of the beta-endorphin fraction by gel chromatography. Plasma beta-endorphin levels decreased significantly (p less than 0.005) after intrathecal morphine from 76 +/- 9.7 to 46.3 +/- 9.1 fmol/ml (mean +/- SE), possibly because of decreased pituitary beta-endorphin secretion in response to alleviation of labor pain.