Evaluation of nitroxides for the study of myocardial metabolism and oxygenation

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Abstract
Electron paramagnetic resonance spectroscopy at the L‐band (1.2 GHz) was used to investigate the redox metabolism and oxygenation within ischemic rat hearts loaded with a variety of six‐ and five‐membered carbocyclic nitroxide spin labels. Both cardiopleged and non‐cardiopleged hearts were studied at room temperature and at physiological temperatures. The results indicate that nitroxides that have greater intracellular partitioning are reduced faster than those that are extracellular. In addition, the six‐membered rings are metabolized much faster than the five‐membered rings. Increased nitroxide radical metabolism was observed in non‐cardiopleged compared with cardiopleged hearts. The oxygen utilization in the ischemic hearts was studied by using the oxygen‐dependent broadening of the nitroxide signals that occurs due to Heisenberg spin exchange. These structurally different nitroxides were evaluated for their sensitivity and suitability as probes of myocardial redox metabolism and oxygenation in the heart.

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