In vivo spin trapping of nitric oxide in mice

We report here an in vivo spin-trapping technique combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (·NO) production in the blood circulation of conscious mice. The method is based on the trapping of nitric oxide (·NO) by a metal-chelator complex consisting of N-methyl-D-glucamine dithiocarbamate (MGD) and reduced iron (Fe²⁺) to form a stable and water-soluble [(MGD)₂-Fe²⁺-NO] complex, which gives rise to a characteristic three-line EPR spectrum of a mononitrosyl-Fe²⁺ complex (a^N= 12.5 G and g_iso=2.04) at ambient temperatures. After simultaneous intravenous injection of sodium nitroprusside (an ·NO donor) and the [(MGD)₂-Fe²⁺] complex into the lateral vein of the mouse tail, the appearance of the three-line spectrum in the blood circulation of the mouse tail was monitored continuously by using an S-band EPR spectrometer, operating at 3.5 GHz. This represents the first spin trapping of ·NO in living animals.