Whole body detection and imaging of nitric oxide generation in mice following cardiopulmonary arrest: Detection of intrinsic nitrosoheme complexes

Ischemic tissues generate nitric oxide (NO) by direct reduction of tissue n itrite under the acidic conditions that occur during ischemia. In view of t he important implications of this enzyme-independent mechanism of NO genera tion on the pathogenesis and treatment of tissue injury, the NO formation i n mice subjected to cardiopulmonary arrest was measured and imaged. Real-ti me measurement of NO generation was performed by detection of naturally gen erated NO-heme complexes in tissues using L-band electron paramagnetic reso nance (EPR) spectroscopy. To distinguish NO generated from nitrite, animals were labeled with isotopically enriched N-15-nitrite. Mice were infused wi th nitrite (70 mg/kg, intravenous), cardiopulmonary arrest induced by an ov erdose of phenobarbital, and transferred to the EPR resonator. Measurements of NO generation were performed on the intact animal at the levels of the head, thorax, and abdomen. At the end of 3 hr, major organs were isolated a nd analyzed for their NO signal. The NO complexes were found to have maximu m levels in lung, heart, and liver. Three-dimensional spatial mapping of th e NO complex in the intact animal subjected to cardiopulmonary arrest was p erformed using EPR imaging techniques. The images also confirmed the maximu m formation in the lungs, heart, and liver. The present data reveal that mi ce subjected to cardiopulmonary arrest generate large amounts of NO, which is nitrite mediated. The observed signal was largely due to heme-bound NO, which accounted for the high concentrations found in these organs. This inc reased NO formation during cardiopulmonary arrest could contribute to the d ifficulty of resuscitation after long periods of arrest. Magn Reson Med 45: 700-707, 2001. (C) 2001 Wiley-Liss, Inc.