A comprehensive understanding of the control of amniotic fluid volume is of major clinical importance. We have identified a vascular pathway within the fetal membranes and fetal surface of the placenta for fluid and solute exchange between the amniotic compartment and fetal blood. This pathway is an important determinant of amniotic fluid volume. Recently, we found expression of vascular endothelial growth factor (VEGF) in the amnion and chorion, and this expression is increased under conditions of enhanced intramembranous absorption. We hypothesize that VEGF is the key regulator of this absorption and factors that stimulate VEGF gene expression in the membranes are important mediators of amniotic fluid volume regulation. In this application, we propose to explore the source and identity of the VEGF stimulatory factors that are activated by blockade of fetal swallowing or fetal hypoxia, conditions that augment intramembranous absorption. The potential factors include PGE2, EGF, TGF, PAP and PDGF derived from the fetal membranes or fetal kidneys. Pregnant sheep will be used as the animal model.
In specific aim 1, we propose to determine which factors in the amniotic fluid or fetal urine are induced by fetal esophageal ligation and whether the kidneys or the membranes are the source of the factors. The effect of the factors on VEGF mRNA and protein expression in amnion cells will be examined.
Specific aim 2 proposes to investigate the role of PGE2 and growth factors on the hypoxic induction of VEGF gene expression in the fetal membranes. The effect of hypoxia on concentration of these factors in the amniotic fluid and fetal urine will be determined. Whether these factors contribute to the hypoxic induction of VEGF will be tested in amnion cells.
In specific aim 3, we propose to examine the regulation of expression and function of the VEGF receptor KDR in amnion cells. The effects of VEGF on KDR mRNA and protein expression in the cells will be explored. The ability of VEGF to stimulate amnion cell proliferation and increase permeability of the amnion/chorin will be delineated. Overall, we will test the hypothesis that augmented intramembranous absorption is caused by up-regulation of VEGF gene expression in the fetal membranes. This is induced by factors in the amniotic fluid that are activated by fetal esophageal ligation or hypoxia. Results from these studies will promote understanding of amniotic fluid volume regulation, and provide important information for diagnosis and management of amniotic fluid disorders in human pregnancy.
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