Determination and characterization of nitric oxide generation in mice by in vivo L-Band EPR spectroscopy.

The authors have shown direct, real-time, in vivo measurement of nitric oxide (NO) in mice by using the water soluble metal chelator complex, N-methyl-D-glucamine dithiocarbamate (MGD), and Fe(II) as monitored by EPR at L-band. The three-line EPR spectrum from the product [(MGD)2-Fe(II)-NO] was observed noninvasively in lipopolysaccharide (LPS)-treated mice. The spectrum was markedly suppressed by the administration, before LPS injection, of phenyl N-tert-butyl nitrone (PBN), an inhibitor of the expression of induced nitric oxide synthase (iNOS). When 15N-arginine was administered to LPS-treated mice, a diagnostic EPR spectrum was observed, consisting of both three- and two-line EPR signals, due to (MGD)2-Fe(II)-14NO and (MGD)2-Fe(II)-15NO, respectively. The results strongly suggested that the NO detected in these experiments was synthesized by iNOS. In vivo EPR measurements of [(MGD)2-Fe(II)-NO] at several regions in the body (from the head to the tail) indicated that the NO was generated mostly in the upper abdomen near the liver. These observations were confirmed by ex vivo EPR measurements on isolated organs where higher NO levels were detected in vivo in the liver and kidney. The spectroscopic results, combined with the pharmacokinetic data, support the model that NO detected in LPS-treated mice was produced mainly in the liver, and that it did not reflect NO-adduct complex accumulated in the liver via the blood circulation.