title: Oxytocin and initiation of human parturition. III. Plasma concentrations of oxytocin and 13,14-dihydro-15-keto-prostaglandin F2 alpha in spontaneous and oxytocin-induced labor at term.
abstract: The plasma concentrations of oxytocin and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured in serial samples collected during the first stage of spontaneous and oxytocin-induced labor in 17 and 15 women, respectively. Four women in late pregnancy served as control subjects, with serial samples collected at similar intervals as during labor. During spontaneous labor, mean plasma oxytocin levels were consistently raised over the levels observed 1 to 2 weeks before the onset of labor and were higher than the levels in the control patients (mean, 19.9 +/- 3.1 pg/ml) and the initial levels in the oxytocin-induced group of women (mean, 17.4 +/- 4.8 pg/ml). The mean plasma oxytocin levels during spontaneous labor (45 +/- 3.9 pg/ml) were similar to those observed during infusion of 4 to 6 mU/min of synthetic oxytocin (49.1 +/- 10.9 pg/ml). Plasma oxytocin levels increased progressively with stepwise increments of the infusion. Plasma PGFM levels also rose during labor, but, in contrast to the oxytocin levels which increased in early labor, plasma PGFM levels did not increase significantly until relatively late in labor, provided the membranes were intact. The state of the membranes had a marked influence on plasma PGFM; patients with spontaneous rupture of membranes had significantly increased PGFM levels when admitted early in labor or when membranes ruptured during labor. This increase in prostaglandin F2 alpha (PGF2 alpha) production does not by itself suffice to initiate labor, as evidenced by the failure of premature rupture of the membranes to initiate labor in a number of patients with elevated PGFM levels in whom labor was then induced with oxytocin. Conversely, oxytocin induction was successful only when PGFM levels increased during the infusion of oxytocin; in the absence of a rise in plasma PGFM, oxytocin induction failed. These data add support to the view that both oxytocin and PGF2 alpha are required for adequate stimulation of the human uterus during labor. In addition, the data suggest that oxytocin rather than PGF2 alpha may be the major stimulus that initiates labor, whereas PGF2 alpha appears responsible for the progress of labor.
mesh_terms: D002584:Cervix Uteri / Q000187:drug effects; D015237:Dinoprost / Q000031:analogs & derivatives*; D005321:Extraembryonic Membranes / Q000187:drug effects; D005260:Female; D005322:Premature Rupture of Fetal Membranes / Q000503:physiopathology; D006801:Humans; D007263:Infusions, Parenteral; D007751:Labor, Induced; D007743:Labor, Obstetric / Q000187:drug effects*; D010121:Oxytocin / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D011247:Pregnancy; D011460:Prostaglandins F / Q000097:blood*; D013997:Time Factors
chemical_list: D011460:Prostaglandins F; C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D010121:Oxytocin; D015237:Dinoprost