Enhanced Vascular Permeability in Solid Tumor Is Mediated by Nitric Oxide and Inhibited by Both New Nitric Oxide Scavenger and Nitric Oxide Synthase Inhibitor

A newly discovered nitric oxide radical scavenger, an imidazolineoxyl N‐oxide derivative, was used to investigate the role of nitric oxide radical (*NO) in the vascular permeability enhancement of solid tumor. Sarcoma‐180 solid tumor in ddY mice was used for this experiment. Electron spin resonance spectroscopy was used to quantitate the reacted and unreacted scavenger. The results showed that extensive extravasation, assessed by intravenous injection of Evans blue, could be greatly suppressed by both *NO scavenger administered orally and *NO synthase inhibitor administrated intraperitoneally. This indicates that *NO is responsible for the vascular permeability in solid tumors.