EFFECTS OF RESTRICTING UTEROPLACENTAL BLOOD-FLOW ON CONCENTRATIONS OF CORTICOTROPIN-RELEASING HORMONE, ADRENOCORTICOTROPIN, CORTISOL, AND PROSTAGLANDIN-E2 IN THE SHEEP FETUS DURING LATE PREGNANCY

We have examined the effects of reduced uterine blood flow and prolonged fetal hypoxemia on the temporal relationship between changes in hormones associated with the activity of the pituitary-adrenal axis (corticotrophin-releasing hormone (CRH), adrenocorticotrophin (ACTH), cortisol, and prostaglandin E2 (PGE2)) in the ovine fetus at 120-125 days of pregnancy, and we sought evidence for placental secretion of CRH and ACTH during prolonged hypoxemia. Uterine blood flow was reduced by placing an adjustable Teflon clamp around the maternal common internal iliac artery to decrease fetal arterial oxygen saturation from mean values of 59.1 +/- 3.3 to 25.7 +/- 4.6% (+/- SEM, n = 10). There was a transient peak in immunoreactive (IR-) CRH at 1-2 h after reducing uterine blood flow. IR-ACTH rose to peak values at +2 h, then gradually decreased to control level by +12 h. Fetal plasma cortisol and PGE2 concentrations were elevated significantly by +2 and +4 h, respectively, and at 20-24 h. The identity of IR-CRH in fetal plasma and in ovine placental extracts was confirmed by HPLC, but there was no consistent umbilical vein - femoral arterial concentration difference for either IR-CRH or IR-ACTH during normoxemia or hypoxemia. We conclude that a sequence of endocrine changes involving CRH, ACTH, PGE2, and cortisol occurs in the fetus during a prolonged reduction in uterine blood flow. However, we did not obtain evidence, for placental secretion of either CRH or ACTH in response to this manipulation.