The Distribution of Radiolabeled Corticotropin-Releasing Factor in Pregnant Rats: An Investigation of Placental Transfer to the Fetuses

Stress during gestation can have serious consequences on the development of the fetus. Many of these effects appear to be mediated by hormones of the hypothalamic-pituitary-adrenal (HPA) axis. Corticotropin-releasing factor (CRF), released by the hypothalamus during times of stress serves to activate release of pituitary hormones and is also present in low levels in rat plasma. Moreover, the uterus contains significant quantities of CRF at implantation sites, probably from local sources. Therefore, the possibility exists that CRF may cross the placenta and activate the fetal HPA axis. However, the ability of CRF to cross the placenta has not been demonstrated. In the present study, pregnant rats were administered radiolabeled CRF intraperitoneally, and the distribution of the labeled product was determined in the fetuses and various maternal organs. High levels of activity were observed in the pregnant females uterus, adrenals, heart and the placentae, but only background levels of activity were detected in the maternal brain. Very low levels of activity were observed in the fetuses, indicating that the transfer of CRF across the placenta is greatly restricted. These findings suggest that maternal CRF has little or no direct effect on the developing fetus during gestational stress