Detection of nitric oxide production in lipopolysaccharide-treated rats by ESR using carbon monoxide hemoglobin.

Release of nitric oxide (NO), from macrophages activated with E. coli lipopolysaccharide (LPS) and endothelial cells, has been proposed using chemiluminescence and spectrophotometry. However these methods can not distinguish NO from NO2-. The present study was aimed to prove in vivo production of NO, by ESR using CO-hemoglobin (HbCO) as a trapping agent of NO in the peritoneal cavity of rats treated with LPS. We detected a broad signal in the recovered HbCO solution. Inositol hexaphosphate induced a three-line hyperfine structure, characteristic of NO-hemoglobin (HbNO). In the arterial blood, ESR signal of HbNO with faint hyperfine structure was detected. NG-Monomethyl-L-arginine inhibited the formation of HbNO. HbNO was not detected in the peritoneal cavity of the LPS-untreated rat given i.p. both NO2- and HbCO. HbNO was, therefore, derived from NO, not from NO2-. These results show that free NO is produced in vivo by the stimulation of LPS.