Heat produces uteroplacental circulatory disturbance in pregnant rats through action of corticotropin releasing hormone (CRH)

There is some evidence showing an existence of corticotropin releasing hormone (CRH) and opioid peptides, including β-endorphin (βEP), in human placenta, whereas physiological roles of the placental peptides in response to stress remain to be elucidated. To clarify the involvement of CRH and opioid system in the uteroplacental circulation in the pregnant rats exposed to heat, we examined the effects of heat and intravenous administration of CRH receptor antagonist α-helical CRH (9-41) on the uteroplacental blood flow, as well as blood CRH, and blood and placental βEP in pregnant rats. Heat did not change uterine blood flow in virgin rats, but reduced uteroplacental blood flow in pregnant rats. The reduced uteroplacental blood flow induced by heat in pregnant rats was reversed by the administration of α-helical CRH. Independent of the status of pregnancy, heat increased blood CRH, which was not reversed by α-helical CRH. Although heat did not change placental βEP, α-helical CRH reduced blood and placenta βEP in pregnant rats. These results suggest that the uteroplacental circulatory disturbance caused by heat is mediated by CRH, possibly through the involvement of CRH receptor in rat placenta. The placental opioid system seems unlikely to be involved in the mediation of uteroplacental circulation. (C) 2000 Harcourt Publisher Ltd.