Prolonged hypoxia upregulates vascular endothelial growth factor messenger RNA expression in ovine fetal membranes and placenta

OBJECTIVE: In ovine fetuses, 4 days of hypoxia resulted in a large increase in urine flow, without the development of polyhydramnios, which suggests that intramembranous absorption of the amniotic fluid was enhanced. Because vascular endothelial growth factor is speculated to be a regulator of intramembranous absorption through increases of membrane vascularity and fluid transport, we hypothesized that hypoxia upregulated vascular endothelial growth factor gene expression in the fetal membranes. STUDY DESIGN: Five near-term ovine fetuses that were subjected to 4 days of hypoxia and 5 age-matched time controls were studied. On day 4, the amnion, chorion, and placenta were collected for cellular localization and quantification of vascular endothelial growth factor messenger RNA and for the determination of vascular endothelial growth factor molecular forms that were expressed. The data were analyzed statistically with the use of t tests and 2-factor analyses of variance. RESULTS: Vascular endothelial growth factor messenger RNA was expressed in the fetal membranes localized to the amniotic epithelium and chorionic cytotrophoblast, and to the villous cytotrophoblast of the placenta. In hypoxic fetuses, vascular endothelial growth factor messenger RNA levels in these cell layers were significantly increased compared with the controls. Five vascular endothelial growth factor molecular forms were identified with vascular endothelial growth factor₁₆₄being the most abundant form expressed. The pattern of expression of the forms was not altered by hypoxia. CONCLUSION: In the near-term ovine fetus, hypoxia induced vascular endothelial growth factor messenger RNA expression in the amnion, chorion, and placenta. This was associated with an increase in intramembranous absorption of amniotic fluid. We speculate that the increased intramembranous absorption was mediated by a vascular endothelial growth factor-induced increase in the transport of amniotic fluid into the fetal membranes.