We evaluated the effect of nitric oxide (NO) on vascular endothelial growth factor (VEGF) gene expression in human A-172 glioblastoma cells and human HepG2 hepatocellular carcinoma cells. The mRNA level of VEGF increased in response to S-Nitroso-N-acetyl-D,L-penicillamine (SNAP) in both cell lines, and increased in mRNA level well coincided with VEGF protein production in A-172 cells. SNAP at 0.5 mM induced maximal stimulation of 4.4 and 3.7 kb VEGF mRNA expression after 6 h about 11 and 8 fold increase, respectively above control level. Similar VEGF mRNA accumulation was observed also with NOR3, another chemical NO generator. To evaluate the effect of SNAP on VEGF mRNA stability, half-lives of VEGF mRNA were measured in A-172 cells cultured with or without 0.5 mM SNAP and treated with actinomycin D (25 microg/ml). Half-life for VEGF mRNA was found to be prolonged about 2.4 fold by SNAP. VEGF expression induced by SNAP was inhibited by guanylate cyclase inhibitors, methylene blue (10 microM) and LY-83583 (1 microM), and by the protein synthesis inhibitor, cycloheximide (25 microg/ml). These results suggest that induction of VEGF gene expression by NO is mediated through guanylate cyclase activity and requires on-going protein synthesis.