Maternal plasma corticotropin-releasing factor (CRF) and CRF-binding protein (CRF-BP) levels in post-term pregnancy: effect of prostaglandin administration.

OBJECTIVE Placental corticotropin-releasing factor (CRF) affects myometrial contractility and the secretion of several uterotonins such as prostaglandins (PGs); however, the activity of CRF is counteracted by CRF-binding protein (CRF-BP). At term and pre-term labor, CRF levels in maternal plasma are highest whereas those of CRF-BP are falling, and the cause of this fall is unknown. Thus, in this study, we investigated the effect of PG administration for labor induction on maternal plasma CRF and CRF-BP concentrations. DESIGN Maternal plasma CRF and CRF-BP levels were assayed before and after (2 h later) induction of labor by intracervical administration of prostaglandin E(2) (PGE(2)), and at delivery in a group of healthy post-term pregnancies (n=18). Controls were women at term out of labor (n=22), who subsequently progressed to deliver a healthy singleton baby. METHODS CRF was measured by two-site immunoradiometric assay, and CRF-BP was assayed by radioimmunoassay. RESULTS Maternal plasma CRF levels were significantly (P<0.0001) lower and CRF-BP significantly (P<0.0005) higher in post-term than in term pregnancies. With respect to induction of labor, 2 mg PGE(2) were sufficient to increase maternal plasma CRF levels at delivery (P<0.005). While 0.5 mg PGE(2) significantly decreased maternal plasma CRF-BP levels at delivery (P<0.001), 2.0 mg PGE(2) significantly reduced CRF-BP concentrations both after 2 h (P<0.05) and at delivery (P<0.0001). CONCLUSIONS In the light of the well-known stimulation of prostaglandin release by CRF, these data suggest a positive feedback effect of PGE(2) on maternal CRF release during induced labor.