Clinical science
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Vascular endothelial growth factor (VEGF) mediates endothelial cell mitogenesis and enhances vascular permeability. VEGF interacts with the endothelium via two membrane-spanning receptors, fms-like tyrosine kinase (Flt)-1 and kinase domain receptor. A soluble form of Flt-1 (sFlt-1) was isolated from endothelial cell media; however, its biological significance is still unknown, with limited data on plasma sFlt-1 levels in disease states. ⋯ Plasma levels of VEGF-complexed sFlt-1 are minimal, despite the presence of excess free sFlt-1. Thus unbound plasma VEGF detected by ELISA may represent the majority of circulating VEGF, and justifies the measurement of plasma VEGF as an indicator of circulating VEGF levels. Furthermore, these results suggest that circulating sFlt-1 may serve as a selective inhibitor of VEGF activity, and that this regulatory mechanism may be altered by pathological conditions.