Applications of in vivo electron paramagnetic resonance (EPR) spectroscopy: Measurements of pO₂ and NO in endotoxin shock

Recent developments of EPR instrumentation that allow the use of large tissue samples or whole animals and the ability to image spatially resolved EPR signals has led to novel applications of EPR spectroscopy in vivo. Utilising a 1 GHz EPR spectrometer with a 3.4-cm birdcage resonator, it was possible to detect and measure nitric oxide and oxygen in the livers of mice with lipopolysaccharide (LPS)-induced septic shock. Nitric oxide was detected as the nitric oxide (NO) complex of Fe-diethyldithiocarbamic acid (Fe-DETC) while pO₂ was measured from the EPR linewidth of the oxygen-sensitive coal material 'gloxy'. LPS treatment stimulated the production of nitric oxide in the liver and the general circulation and the oxygenation of liver tissue was decreased. Selective placement of the EPR probes allowed images of nitric oxide and oxygen to be obtained in the liver. The spectral and spatial information obtained with this technique will allow improved understanding of the pathophysiology of such diseases.