Electron spin resonance detection of nitric oxide generation in major organs from LPS-treated rats

The increased production of nitric oxide (NO) has been implicated as the ba sis for myocardial dysfunction and the lack of response to vasoconstrictors during endotoxin shock induced by lipopolysaccharide (LPS). Our objective was to evaluate and compare NO production in major organs of rats treated w ith LPS, 1 or 14 mg/kg. A NO spin-trapping technique using electron spin re sonance (ESR) spectroscopy has been used to study NO production in the live r, the kidney, the aorta, and the heart. The method was based on the trappi ng of NO by a metal-chelator complex consisting of N-methyl-D-glucamine dit hiocarbamate (MGD) and reduced iron (Fe2+) to form a stable [(MGD)(2)-Fe2+- NO] complex, giving rise to a characteristic triplet ESR spectrum with g = 2.04 and a(N) = 12.65 G: Iron was quantified in the different organs to stu dy the [(MGD)(2)-Fe2+] complex distribution. Six hours after intravenous in jection of 1 or 14 mg/kg of LPS, we observed large increases in the [(MGD)( 2)-Fe2+-NO] adduct signal in the liver, the kidney, and in the aorta, stron gly suggesting an increased production of NOln these organs. The [(MGD)(2)- Fe2+-NO] adduct was also detected in the heart, 6 h after injection of LPS. Moreover, we observed dose-dependent increases in [(MGD)(2)-Fe2+-NO] adduc t in the heart, whereas no changes were observed in the other organs. Concu rrently, the [(MGD)(2)-Fe2+-NO] adduct was not detected in the blood from r ats treated with LPS, although circulating nitrosylhemoglobin, nitrite, and nitrate levels increased. The spin-trapping technique allowed us to monito r organ-specific formation of NO after LPS administration and for the first time demonstrated direct NO production in aorta and heart of LPS-treated a nimals.