Plasma oxytocin levels during human pregnancy and labor as determined by radioimmunoassay

Plasma oxytocin in human pregnancy and parturition

“…Using a radioimmunoassay, CHARD et al [6] could not detect measurable amounts of oxytocin during pregnancy and LEAKE et al [36] found that values throughout pregnancy did not differ significantly from those in non-pregnant women. However, most of the other authors reported a rising trend with gestation, either on the basis of cross-sectional data [30,35,44] or serial maternal plasma samples [15,50]. Our values are consistent with those published by VASICKA et al [50], but the oxytocin concentrations reported by DAWOOD etal.…”

“…Subsequently, the same investigators [31] reported measurable levels of oxytocin during labor, with a maximum of positive values during delivery. Their results have been confirmed by others [12,13,14,15,30,32,35,36,44,50] but with wide differences in absolute concentrations and trends during pregnancy and labor. The study of oxytocin in the circulation is hampered by the fact that this hormone is rapidly broken down by oxytocinase, and immediate cooling of samples is required to reduce enzymic activity [35].…”

“…Their results have been confirmed by others [12,13,14,15,30,32,35,36,44,50] but with wide differences in absolute concentrations and trends during pregnancy and labor. The study of oxytocin in the circulation is hampered by the fact that this hormone is rapidly broken down by oxytocinase, and immediate cooling of samples is required to reduce enzymic activity [35]. It has been demonstrated that the plasma oxytocin concentration rises gradually during pregnancy and first-stage labor, the highest levels being observed during the second stage [13,31], and LEAKE et al [36] reported a marked increase in oxytocin coincident with delivery of the fetal head.…”

“…Continuous lumbar epidural anesthesia (CLEA) led to a reduction of circulating oxytocin levels and increased the forceps delivery rate. An additional and seemingly constant finding has been that at spontaneous vaginal delivery and emergency cesarean section, the concentrations of oxytocin in umbilical/arterial and venous plasma are much higher than the maternal plasma levels [8,14,18,35,36,44,50]. This may indicate that the fetal brain contributes to the initiation/maintenance of human labor, a suggestion already made by BELL and ROBSON [3].…”

Study of oxytocin receptor in human myometrium using highly specific 3H-labeled oxytocin.

“…We know of no reports concerning the mechanism of the action of OT in the uterus during parturition, even though there have been some studies on plasma OT levels (Chard et al, 1971;Kumaresan et al, 1974;Dawood et al, 1977) and on the specific binding site for3H-OT in the uterus (Soloff et al, 1974). One of the reasons for such a small number of reports is the lack of isotopically labeled OT with a high specific activity as well as high biologic activity.…”