SPIN-LABEL OXIMETRY TO ASSESS EXTRACELLULAR OXYGEN DURING MYOCARDIAL-ISCHEMIA

We describe real-time measurement of myocardial oxygen consumption dur ing ischemia in the intact heart. Measurement of extracellular oxygen concentration during myocardial ischemia by spin label oximetry has be en limited by ischemia-induced reduction of the neutral, water-soluble nitroxide TEMPONE. We have overcome this problem by encapsulating the nitroxides. Isolated immature (7-10 d old) rabbit hearts (n=8) were p erfused aerobically within the cavity of a loop gap resonator with bic arbonate buffer containing an oxygen-sensitive, lipid-soluble nitroxid e (N-14-TEMPO laurate in FC-43 perfluorocarbon micelles) and a much le ss oxygen-sensitive and positively charged nitroxide (N-15-TEMPO choli ne in multilamellar vesicles) as an internal standard. The ratio of th e ESR signal amplitudes of these nitroxides was used as a sensitive in dex of oxygen concentration. Sequestration of the nitroxides decreased their reduction rate by ascorbate in comparison with nonsequestered n itroxides. Hearts were subjected to 60 min of global no-flow ischemia at 20 degrees C. Extracellular oxygen content (mean+/-SD) during aerob ic perfusion was 1195+/-55 mu mol/liter. The electron spin resonance s ignal from TEMPO laurate increased with the onset and progression of i schemia, consistent with a decrease in extracellular oxygen, while the signal for TEMPO choline was relatively unchanged. Extracellular oxyg en content after 40 and 60 min of ischemia was reduced to 393+/-27 mu mol/liter (p <.05) and 61+/-5 mu mol/liter (p <.05), respectively. We conclude that spin-label oximetry can directly and precisely measure m yocardial oxygen consumption at constant temperature during ischemia i n the intact heart. Copyright (C) 1996 Elsevier Science Inc.