Nitric oxide mediates the mitogenic effects of insulin and vascular endothelial growth factor but not of leptin in endothelial cells

The regulation of vascular wall homeostasis by nitric oxide (NO) generated by endothelium is being intensively studied. In the present paper, the invo lvement of NO in the vascular endothelial growth factor (VEGF), insulin or leptin-stimulated proliferation of human endothelial cells (HUVEC) was meas ured by [H-3]thymidine or bromodeoxyuridine incorporation. VEGF and insulin , but not leptin, increased NO generation in HUVEC, as detected with ISO-NO electrode. Proliferation of HUVEC induced by leptin was not changed or was higher in the presence of N-omega-nitro-L-arginine methyl ester (L-NAME) a nitric oxide synthase (NOS) inhibitor. In contrast, L-NAME blunted the pro proliferative effect of VEGF and insulin. Furthermore, we demonstrated that , in human arterial smooth muscle cells (hASMC) transfected with endothelia l NOS (eNOS) gene, the generation of biologically active VEGF protein was N O-dependent. inhibition of NO generation by L-NAME decreased the synthesis of VEGF protein and attenuated HUVEC proliferation induced by conditioned m edia from transfected hASMC. Endothelium-derived NO seems to participate in VEGF and insulin, but not leptin, mitogenic activity. Additionally, the sm all amounts of NO released from endothelial cells, as mimicked by eNOS tran sfection into hASMC, may activate generation of VEGF in subendothelial smoo th muscle cells, leading to increased synthesis of VEGF protein necessary f or turnover and restitution of endothelial cells.