Lack of beta-endorphin plasma level rise in oxytocin-induced labor.

beta-Endorphin (beta-EP), beta-lipotropin (beta-LPH) and cortisol plasma levels were measured during labor in 18 pregnant women. In 7 cases labor progressed spontaneously and in 11 cases oxytocin (5 mIU/min) was administered to stimulate uterine contractions. In control and oxytocin-treated subjects hourly blood samples were taken until delivery. In spontaneous labor all three hormones showed a progressive and significant increase until parturition. In oxytocin-treated patients, however, both beta-EP and beta-LPH remained constant until parturition. Cortisol levels in oxytocin-treated patients presented a significant increase but reached values significantly lower than in control patients. These results indicate that women with uterine hypocontractility during labor requiring oxytocin showed no rise in their plasma beta-EP and beta-LPH and a blunted cortisol rise during oxytocin administration.