Changes in Amniotic Fluid Immunoreactive Corticotropin-Releasing Factor (CRF) and CRF-Binding Protein Levels in Pregnant Women at Term and during Labor1

Corticotropin-releasing factor (CRF)-binding protein (CRF-BP) modulates the activity of the hypothalamus-pituitary-adrenal axis during pregnancy, counteracting the actions of circulating or locally produced CRF. The aim of the present study was to evaluate CRF and CRF-BP levels in amniotic fluid of healthy pregnant women during the last 4 weeks of gestation and during spontaneous labor at term. A cross-sectional study was conducted on amniotic fluid collected from pregnant women (n = 68), subdivided into two groups: 1) not in labor (n = 31), and 2) in labor (n = 37). CRF-BP was measurable in all specimens of amniotic fluid, but at 37 weeks of pregnancy the concentration in amniotic fluid was lower (10-fold) than that in maternal plasma (P < 0.01). Pregnant women at 39 and 40 weeks gestation had amniotic fluid CRF-BP levels significantly lower than those at 37 weeks (P < 0.01), and pregnant in women in labor had significantly lower levels than women at term but not in labor (P < 0.01). CRF levels in amniotic fluid and plasma collected in women at 40 weeks gestation not in labor or in labor were significantly higher than those at 37 weeks (P < 0.01). During the last 4 weeks of gestation, amniotic fluid CRF levels in women not in labor did not significantly differ from those obtained at term labor. During the last weeks of pregnancy, amniotic fluid CRF-BP levels decrease and are inversely correlated to CRF levels. The decrease in amniotic fluid CRF-BP at term, augmenting the amount of free CRF, supports the hypothesis that labor is associated with significant changes in local autocrine and paracrine factors that may affect PG release and myometrial contractility, contributing to the mechanism of parturition.