ENDOGENOUS REGULATION OF ANGIOGENESIS IN THE RAT AORTA MODEL - ROLE OF VASCULAR ENDOTHELIAL GROWTH-FACTOR

The purpose of this study was to investigate the role of vascular endo thelial growth factor (VEGF) in the rat aorta model of angiogenesis. F reshly cut aortic rings generated microvascular outgrowths in serum-fr ee collagen gel culture, Angiogenesis was reduced to 10% when the expl ants were embedded in collagen 10 to 14 days after excision from the a nimal, Immunochemical studies of conditioned medium demonstrated secre tion of VEGF by the aortic cultures, Levels of VEGF decreased during t he second week of culture when the explants became quiescent and micro vessels stopped growing. Treatment of quiescent aortic rings with exog enous VEGF stimulated angiogenesis and restored microvascular growth t o values observed in cultures of freshly cut explants, Reverse transcr iptase polymerase chain reaction of vasoformative collagen gel culture s of rat aorta demonstrated the expression of the alternatively splice d isoforms VEGF(165), VEGF(189), and the high affinity VEGF receptor f lk-1. Reverse transcriptase-polymerase chain reaction of rat aorta-der ived cell strains confirmed the presence of VEGF(165) and VEGF(189) in endothelial cells, smooth muscle cells, and fibroblasts. The flk-1 re ceptor was expressed by endothelial cells but not by fibroblasts or sm ooth muscle cells, which is consistent with the endothelial target spe cificity of VEGF, The spontaneous angiogenic response of freshly cut a ortic rings was inhibited by 70% with a neutralizing antibody against VEGF, whereas nonimmune IgG had no effect (P < 0.001), These findings provide evidence for a VEGF-mediated autocrine/paracrine regulation of angiogenesis in the rat aorta model.