Immunoreactive corticotropin-releasing factor and corticotropin during pregnancy, labor and puerperium.

Concentrations of immunoreactive corticotropin releasing factor (CRF) and corticotropin (ACTH) in the plasma were studied in healthy pregnant women. Concentration of CRF was near the detection limit of the assay (2.5 pmol/l) until the 16th week of pregnancy, increasing thereafter significantly towards term: the mean values (+/- S.E.) at weeks 8-11, 12-15, 16-19, 20-23, 24-27, 28-31, 32-35, and 36-40 were 2.9 +/- 0.42, 2.9 +/- 0.72, 5.2 +/- 1.1, 10.2 +/- 5.8, 14.6 +/- 2.0, 32.8 +/- 4.8, 63.6 +/- 9.2, and 187 +/- 39 pmol/l, respectively. The mean concentration of CRF did not increase during labor, and it decreased rapidly after delivery. On the contrary, the mean plasma level of ACTH increased only slightly during late pregnancy, but during labor the increase was significant. These findings suggest that CRF in maternal circulation is not primarily involved in the regulation of maternal ACTH secretion, and the stress of labor does not increase the release of CRF, which probably originates mainly from the placenta.