eNOS, NO, and the activation of ERK and AKT signaling at mid-gestation and near-term in an ovine model of intrauterine growth restriction.

Intrauterine growth restriction (IUGR) is a disease responsible for neonatal morbidity and mortality and perinatal death affecting 8% of all pregnancies. In sheep, IUGR that mimics the human IUGR disease closely can be brought on by environmental hyperthermia. Endothelial nitric oxidase synthase (eNOS) and nitric oxide (NO) are important in the regulation of blood flow in the fetal-placental circulation and are modulated by several factors including hypoxia. eNOS activity is also regulated by the phosphorylation of ERK1/2 and AKT proteins in various tissues. In a hyperthermic (HT) ovine model of IUGR with systemic hypertension and increased blood flow resistance, our objective was to determine the relationship between p-ERK, p-AKT, eNOS, and NO concentrations in the placenta, uterine, and umbilical vessels at mid-gestation and near-term. Eight pregnant ewes were exposed to hyperthermic conditions for either 55 or 80 days to induce IUGR. Sheep necropsies were performed at mid-gestation and near-term for collection of placentomes, umbilical vessels, and the uterine artery. Tissues were assessed for eNOS mRNA and protein, and p-ERK and p-AKT protein. Blood was collected for NO determination at the time of necropsy. Placental insufficiency and IUGR (PI-IUGR) pregnancies demonstrated: 1) reduced placental weight at mid-gestation and reduced placental and fetal weight near-term, 2) no changes in eNOS protein concentration in the uterine artery and umbilical vessels, but an increase in NO in umbilical vein blood at both time points, 3) no significant changes in signal transduction makers (ERK/AKT) in placental tissue at mid-gestation but a significant increase near-term in cotyledon tissues, and 4) an increase in p-AKT in the uterine vessels at term. The near-term findings of increased placental p-ERK and p-AKT proteins and umbilical vein NO concentration suggest one mechanism responsible for the increase in placental eNOS previously described in this PI-IUGR model characterized by fetal systemic hypertension and abnormal umbilical artery Doppler velocimetry.