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Near-infrared (NIR) spectroscopy is a noninvasive technique that uses the differential absorption properties of hemoglobin to evaluate skeletal muscle oxygenation. Oxygenated and deoxygenated hemoglobin absorb light equally at 800 nm, whereas at 760 nm absorption is primarily from deoxygenated hemoglobin. Therefore, monitoring these two wavelengths provides an index of deoxygenation. To investigate whether venous oxygen saturation and absorption between 760 and 800 nm (760-800 nm absorption) are correlated, both were measured during forearm exercise. Significant correlations were observed in all subjects (r = 0.92 +/- 0.07; P < 0.05). The contribution of skin flow to the changes in 760-800 nm absorption was investigated by simultaneous measurement of skin flow by laser flow Doppler and NIR recordings during hot water immersion. Changes in skin flow but not 760-800 nm absorption were noted. Intra-arterial infusions of nitroprusside and norepinephrine were performed to study the effect of alteration of muscle perfusion on 760-800 nm absorption. Limb flow was measured with venous plethysmography. Percent oxygenation increased with nitroprusside and decreased with norepinephrine. Finally, the contribution of myoglobin to the 760-800 nm absorption was assessed by using 1H-magnetic resonance spectroscopy. At peak exercise, percent NIR deoxygenation during exercise was 80 +/- 7%, but only one subject exhibited a small deoxygenated myoglobin signal. In conclusion, 760-800 nm absorption is 1) closely correlated with venous oxygen saturation, 2) minimally affected by skin blood flow, 3) altered by changes in limb perfusion, and 4) primarily derived from deoxygenated hemoglobin and not myoglobin.

Addition of insulin or a physiological ratio of ketone bodies to buffer with 10 mM glucose increased efficiency (hydraulic work/energy from O2 consumed) of working rat heart by 25%, and the two in combination increased efficiency by 36%. These additions increased the content of acetyl CoA by 9- to 18-fold, increased the contents of metabolites of the first third of the tricarboxylic acid (TCA) cycle 2- to 5-fold, and decreased succinate, oxaloacetate, and aspartate 2- to 3-fold. Succinyl CoA, fumarate, and malate were essentially unchanged. The changes in content of TCA metabolites resulted from a reduction of the free mitochondrial NAD couple by 2- to 10-fold and oxidation of the mitochondrial coenzyme Q couple by 2- to 4-fold. Cytosolic pH, measured using 31P-NMR spectra, was invariant at about 7.0. The total intracellular bicarbonate indicated an increase in mitochondrial pH from 7.1 with glucose to 7.2, 7.5 and 7.4 with insulin, ketones, and the combination, respectively. The decrease in Eh7 of the mitochondrial NAD couple, Eh7NAD+/NADH, from -280 to -300 mV and the increase in Eh7 of the coenzyme Q couple, Eh7Q/QH2, from -4 to +12 mV was equivalent to an increase from -53 kJ to -60 kJ/2 mol e in the reaction catalyzed by the mitochondrial NADH dehydrogenase multienzyme complex (EC 1.6.5.3). The increase in the redox energy of the mitochondrial cofactor couples paralleled the increase in the free energy of cytosolic ATP hydrolysis, delta GATP. The potential of the mitochondrial relative to the cytosolic phases, Emito/cyto, calculated from delta GATP and delta pH on the assumption of a 4 H+ transfer for each ATP synthesized, was -143 mV during perfusion with glucose or glucose plus insulin, and decreased to -120 mV on addition of ketones. Viewed in this light, the moderate ketosis characteristic of prolonged fasting or type II diabetes appears to be an elegant compensation for the defects in mitochondrial energy transduction associated with acute insulin deficiency or mitochondrial senescence.

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In situ and perfused rat livers showed a spon- .) The existence of such light emission, which should be termed "low-level chemiluminescence" to differentiate it from the more effective photoemission of the luciferin/luciferase systems (5, 6), was soon related to oxygendependent chain reactions involving biological lipids (3-5). This early work lay fallow for years, notwithstanding the reports by Stauff and Ostrowski on the chemiluminescence of mitochondria (7) and Howes and Steele on the chemiluminescence of microsomes (8, 9), both isolated from rat liver. The more recent reports by Nakano et al. (10) and Sugioka and Nakano (11) of light emission during lipid peroxidation and other oxidative reactions (12) in microsomes revived interest in the phenomenon and suggested chemiluminescence as a tool for the investigation of the radical reactions of lipid peroxidation under physiological conditions. We have recently reported that maximal light emission in isolated mitochondria and microsomes (13) and in submitochondrial particles (14) requires an electron transfer system, hydroperoxide, and oxygen, and that hydroperoxide-supplemented cytochrome c provides a chemiluminescent model system suitable for the elucidation of some of the molecular mechanisms responsible for light emission (15). On the other hand, isolated cells such as amoebae (16) and phagocytizing leukocytes (17) also have been found to be effective chemiluminescent sources.The most important aspect of the organ chemiluminescence is that it gives readily detectable, continuously monitorable, noninvasive signals of oxidative metabolism. This article explores the possibility of continuously monitoring the metabolism of exposed or fiberoptic probed organs in vivo by the chemiluminescent technique. In this paper we report the spontaneous and hydroperoxide-induced chemiluminescence of the in situ and perfused rat liver, as well as a partial spectral analysis of the chemiluminescence of the perfused liver. Light emission seems to indicate the generation of shkrt-lived free radicals and excited states derived from the side reactions of the free radical process of lipid peroxidation. A preliminary report on light emission has been published elsewhere (13). MATERIALS AND METHODSPhoton Counting. A single-photon-counting apparatus was used (Fig. 1). Both an EMI 9658 photomultiplier, responsive in the range 300-900 nm, with an applied potential of -1.2 kV (dark current: 20-30 counts per second), and an RCA 8850 photomultiplier, responsive in the range 300-650 nm, with an applied potential of -1.8 kV (dark current: 300-400 counts per second) were used. Phototube output was connected to an amplifier-discriminator (model 1121; Princeton Applied Res., Princeton, NJ) adjusted for single photon counting and connected to both a frequency counter (Heathkit IB 1100, Heath, Benton Harbor, MI) and a recorder. The EMI phototube, cooled .down to -400C by a thermoelectric cooler (EMI-Gencom, Plainview, NY) and the RCA phototube were placed in an Ortec housing, sealed and su...

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Simultaneous measurements of phosphocreatine (PCr) and oxyhemoglobin (HbO2) saturation were made during recovery from exercise in calf muscles of five male subjects. PCr was measured using magnetic resonance spectroscopy in a 2.0-T 78-cm-bore magnet with a 9-cm-diam surface coil. Relative HbO2 saturation was measured as the difference in absorption of 750- and 850-nm light with use of near-infrared spectroscopy. The light source and detectors were 3 cm apart. Exercise consisted of isokinetic plantar flexion in a supine position. Two 5-min submaximal protocols were performed with PCr depletion to 60% of resting values and with pH values of > 7.0. Then two 1-min protocols of rapid plantar flexion were performed to deplete PCr values to 5-20% of resting values with pH values of < 6.8. Areas of PCr peaks (every 8 s) and HbO2 saturation (every 1 s) were fit to a monoexponential function, and a time constant was calculated. The PCr time constant was larger after maximal exercise (68.3 +/- 10.5 s) than after submaximal exercise (36.0 +/- 6.5 s), which is consistent with the effects of low pH on PCr recovery. HbO2 resaturation approximated submaximal PCr recovery and was not different between maximal (29.4 +/- 5.5 s) and submaximal (27.6 +/- 6.0 s) exercise. We conclude that magnetic resonance spectroscopy measurements of PCr recovery and near-infrared spectroscopy measurements of recovery of HbO2 saturation provide similar information as long as muscle pH remains near 7.0.

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