Near-Infrared and Infrared Imaging
Analysis of Lipid Metabolism and Energy Expenditure
Near-infrared (1000 - 3000 nm) spectrometry, which employs an external light source for determination of chemical composition, has been previously utilized for industrial determination of the fat content of commercial meat products, for in vivo determination of body fat, and in our laboratories for determination of lipoprotein composition in carotid artery atherosclerotic plaques. Infrared (3000 - 5000 nm) imaging, which measures the surface temperature of objects, was previously examined for quantitation of energy expenditure. However, no previous studies have examined combined near-IR/IR imaging as a tool for the determination of energy expenditure. The purpose of this study was to utilize near-IR and IR spectrometry under a variety of experimental conditions for determination of superficial lipid composition and surface heat emission in rats. Results demonstrate that near-IR spectrometry was capable of predicting the genotype of Zucker obese rats before the development of obesity (3 and 17 days of age). Pharmacologic analysis of the dose-dependent effects of norepinephrine (NE) and angiotensin II (AII) administration on superficial interscapular lipid composition by near-IR spectrometry demonstrated that both agents mobilized lipids albeit with different lipid spectral profiles. Using a tunable-range video camera with different band pass filters, near-IR imaging of adult obese rats demonstrated increases in superficial lipid composition. Moreover, IR imaging with the tunable-range video camera allowed for regional-specific measurements of surface heat emission in conscious, freely moving rats. Following treatment with isoproterenol (ISO) and AII, tail heat emission increased, but dorsal body heat emission differed between the two pharmacologic agents. Chronic administration of low doses of AII resulted in an increase in dorsal surface heat emission. Collectively, these results demonstrate that with a single-instrument, indexes of superficial lipid composition and surface heat emission can be obtained quickly and noninvasively for the analysis of energy expenditure.
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