Vascular endothelial growth factor and de novo mammalian angiogenesis.

The time course and potency of the de novo angiogenic response to vascular endothelial growth factor isoform 165 (VEGF165) at approximate physiologic doses was assessed using the nonsurgical mesenteric-window angiogenesis assay in adult rats. Daily i.p. injections of VEGF165 at 4.8, 48, and 480 pM were given for Days 0-4, controls receiving the vehicle. Groups of 10 animals per treatment group were sacrificed on Days 7, 14, and 21. Using microscopic morphometry and image analysis, the vascularized area, a measure of microvascular spatial extension, and the microvascular length, a measure of microvascular density, were measured. At 4.8 and 480 pM, VEGF165 induced significant angiogenesis as early as on Day 7, suggesting a direct angiogenic effect. This very rapid angiogenic response to VEGF165 is distinct from other angiogenesis reactions, including angiogenesis induced by basic fibroblast growth factor, studied using the same methodology. During the early angiogenic phase, the increase in microvascular spatial expansion dominated over the increase in microvascular density. The specific response to VEGF165 peaked on Day 7 for the 4.8 pM dose and on Day 14 for the 480 pM dose, which was the more potent. It is, moreover, noteworthy that no statistically significant response was induced by the intermediate dose of VEGF165 (48 pM) at any observation time. The data thus suggest that, although VEGF165 at near physiologic doses apparently acts as a direct angiogen, its dose-related effect in terms of angiogenesis is nonlinear.