Effect of tumor VEGF secretion. The rate of VEGF secreted by tumor cells and the tumor isoform secretion ratio VEGF165:VEGF121 induces whole-body changes in the distribution of VEGF. A, Effect of tumor VEGF secretion rate on the steady-state free VEGF concentration in the body. Gray circles indicate the secretion rate used in the current model, 0.56 molecules/cell/s. B, Steady-state free VEGF concentration in the body. Gray circles indicate the ratio used in the current model, VEGF165:VEGF121 = 50%:50% in the tumor. C, Distribution of free, receptor-, and matrix-bound VEGF: black, unbound VEGF; light gray, receptor-bound VEGF; dark gray, VEGF bound to GAG chains in the extracellular matrix and basement membranes.