CORTICOTROPIN-RELEASING HORMONE-BINDING PROTEIN (CRH-BP) - PLASMA-LEVELS DECREASE DURING THE 3RD TRIMESTER OF NORMAL HUMAN-PREGNANCY

In pregnancy, maternal plasma corticotropin releasing hormone (CRH) co ncentrations rise substantially in the third trimester and fall rapidl y post-partum. A binding protein (BP) specific for CRH exists in the h uman circulation which inactivates CRH, thus possibly explaining why m aternal ACTH does not rise outside normal limits throughout gestation. We here describe the measurement of CRH-BP directly in plasma during human pregnancy using a radioimmunoassay that is not affected by the p resence of the high plasma levels of CRH that occur at this time. In 1 19 healthy non-pregnant individuals, mean CRH-BP levels were 4.46 nmol /L +/- 1.0 (SD), with a wide range of 1.81-7.24 nmol/L. Plasma CRH-BP in 34 pregnant women randomly sampled during the first and second trim esters also averaged 4.46 nmol/L +/- 1.54, with individual values rang ing from 1.59-7.51 nmol/L and there was no correlation of CRH-BP level s with gestational age. In a group of 14 women sampled sequentially th roughout the third trimester, plasma CRH-BP averaged 4.56 nmol/L +/- 1 .70 at 30-35 weeks gestation and fell dramatically to 1.84 nmol/L +/- 0.43 at weeks 38-40 (P < 0.001). The post partum recovery in CRH-BP le vels occurred within 48 hours of delivery. These results indicate that there is an increase in the availability of free, potentially bioacti ve CRH at term to stimulate the release of ACTH from the maternal pitu itary and/or to act at a peripheral, non-pituitary CRH receptor(s).