Concentration of free vascular endothelial growth factor and its soluble receptor, sFlt-1 in the maternal and fetal circulations of normal term pregnancies at high and low altitudes

Objective: Vascular endothelial growth factor (VEGF) is regulated by hypoxia that is essential for placental development. It is antagonized by a soluble form of its receptor (sFlt-1). The purpose of this study was to measure these factors in the maternal and the cord bloods, at low and high altitude. Methods: Samples were collected from full term births normal pregnant women. Free (unbound) VEGF and sFlt-1 levels were measured in plasma samples from cord and maternal blood for each subject by enzyme-linked immunosorbent assay (ELISA) using commercially available kits from R&D systems, UK (Cat # DVE00 and Cat # SVR100B, respectively). Results: At high altitude, the average maternal free VEGF in pg/ml was significantly (p < 0.001) lower than that of the cord level (71.30 +/- 282.14 and 431.35 +/- 424.31, respectively). On the other hand, the average maternal sFlt-1 was significantly (p < 0.001) higher than that of the cord level (8205.41 +/- 6244.72 and 1811.74 +/- 3469.30, respectively). At low altitude, the average maternal free VEGF was significantly lower than that of the cord level (0.47 +/- 0.89 and 483.44 +/- 457.31, respectively, p < 0.001). On the other hand, the average maternal sFlt-1 was significantly higher than that of the cord level (9267.82 +/- 6345.68 and 958.66 +/- 1359.92, respectively, p < 0.001). There were no significant differences by altitude. Conclusion: Secretion of sFlt-1 appears to be polarized, in that concentrations are higher in the maternal compartment than on the fetal side at both high and low altitudes. This may be a normal physiological phenomenon to permit angiogenesis in the placenta and fetus while protecting the mother. Chronic exposure to hypobaric hypoxia at high altitude does not affect these distributions.