Plasma prostaglandin metabolites in human labor.

To elucidate the role of prostaglandins in initiating uterine contractions we studied the concentrations of 13,14-dihydro-15-keto-PGE2 (PGE2-M) and 13,14-dihydro-15-keto-PGF2alpha (PGF2alpha-M) in peripheral plasma of pregnant patients. The concentrations of PGE2-M and PGF2alpha-M in pregnant patients at term not in labor were not significantly different from those at midpregnancy. Induction of labor at term pregnancy caused a significant rise of both PGE2-M and PGF2alpha-M. During spontaneous labor there were no significant minute-to-minute fluctuations of plasma PGE2-M and PGF2alpha-M and their concentrations were not different from those at oxytocin-induced labor. Initiation of uterine contractions and abortion at midpregnancy by the intra-amniotic infusion of hypertonic saline was not associated with any change in PGE2-M concentration and a rise in PGF2alpha-M was noted in only one of five patients. The vaginal administration of PGE2 and the intra-amniotic infusion of PGF2alpha were associated in each case with a significant rise of both prostaglandin metabolites. It is concluded that the rise of prostaglandin metabolites in peripheral plasma is secondary to the initiation of uterine contractions at term pregnancy. Such a rise is not usually observed after the initiation of uterine contractions by hypertonic saline at midpregnancy.