 VEGF and ang-1 are involved in endothelial tube formation.Angiopoietin-1 and angiopoietin-2 are modulators of endothelial permeability and barrier function.Endothelial cells secrete angiopoietin-2 for autocrine signaling while parenchymal cells of the extravascular tissue secrete angiopoietin-2 onto endothelial cells for paracrine signaling, which then binds to the extracellular matrix and is stored within the endothelial cells.