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 horm one (CRH) and opioid peptides, including beta-endorphin (beta EP), in human placenta, whereas physiological roles of the placental peptides in respons e to stress remain to be elucidated. To clarify the involvement of CRH and opioid system in the uteroplacental circulation in the pregnant rats expose d to heat, we examined the effects of heat and intravenous administration o f CRH receptor antagonist alpha-helical CRH (9-41) on the uteroplacental bl ood how, as well as blood CRH, and blood and placental beta EP in pregnant rats. Heat did not change uterine blood flow in virgin rats, but reduced ut eroplacental blood flow in pregnant rats. The reduced uteroplacental blood flow induced by heat in pregnant rats was reversed by the administration of alpha-helical CRH. Independent of the status of pregnancy, heat increased blood CRH, which was not reversed by alpha-helical CRH. Although heat did n ot change placental beta EP, alpha-helical CRH reduced blood and placenta b eta EP in pregnant rats. These results suggest that the uteroplacental circ ulatory disturbance caused by heat is mediated by CRH, possibly through the involvement of CRH receptor in rat placenta. The placental opioid system s eems unlikely to be involved in the mediation of uteroplacental circulation . (C) 2000 Harcourt Publishers Ltd.