Spin label oximetry to assess extracellular oxygen during myocardial ischemia.
We describe real-time measurement of myocardial oxygen consumption during ischemia in the intact heart. Measurement of extracellular oxygen concentration during myocardial ischemia by spin label oximetry has been 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 perfused aerobically within the cavity of a loop gap resonator with bicarbonate buffer containing an oxygen-sensitive, lipid-soluble nitroxide (14N-TEMPO laurate in FC-43 perfluorocarbon micelles) and a much less oxygen-sensitive and positively charged nitroxide (15N-TEMPO choline in multilamellar vesicles) as an internal standard. The ratio of the ESR signal amplitudes of these nitroxides was used as a sensitive index of oxygen concentration. Sequestration of the nitroxides decreased their reduction rate by ascorbate in comparison with nonsequestered nitroxides. Hearts were subjected to 60 min of global no-flow ischemia at 20 degrees C. Extracellular oxygen content (mean +/- SD) during aerobic perfusion was 1195 +/- 55 mumol/liter. The electron spin resonance signal from TEMPO laurate increased with the onset and progression of ischemia, consistent with a decrease in extracellular oxygen, while the signal for TEMPO choline was relatively unchanged. Extracellular oxygen content after 40 and 60 min of ischemia was reduced to 393 +/- 27 mumol/liter (p < .05) and 61 +/- 5 mumol/liter (p < .05), respectively. We conclude that spin-label oximetry can directly and precisely measure myocardial oxygen consumption at constant temperature during ischemia in the intact heart.
Baker
J E
JE
Department of Cardiothoracic Surgery, Medical College of Wisconsin, Milwaukee 53226, USA.
Froncisz
W
W
Joseph
J
J
Kalyanaraman
B
B
D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005240:Feasibility Studies; D005609:Free Radicals; D066298:In Vitro Techniques; D008081:Liposomes; D008823:Micelles; D017202:Myocardial Ischemia / Q000097:blood*; D009589:Nitrogen Oxides; D010084:Oxidation-Reduction; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010477:Perfusion; D011817:Rabbits; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl / Q000032:analysis*
D005609:Free Radicals; D008081:Liposomes; D008823:Micelles; D009589:Nitrogen Oxides; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl; C039900:nitroxyl; D010100:Oxygen