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Publication AbstractsORIGINAL RESEARCHVallerand AL, Zamecnik J, Jones PJH, Jacobs IAviat Space Environ Med 1999; 70:42-50. AbstractBackground: To characterize the important changes in the selection and mobilization of metabolic fuel during cold stress, six males rested for 3 h at 29°C and at 5°C dressed only in shorts while 2H5 glycerol, 1-13C palmitate and 6,6 2H2 glucose were continuously infused for 3 h in each condition to determine their rate of turnover (R). Methods: Metabolic rate (M) as well as rates of carbohydrate (CHO) and lipid oxidation (FAT) were assessed by indirect calorimetry whereas all isotopic enrichments were determined by mass spectrometry. Results: Cold exposure decreased rectal and mean skin temperatures and increased M, FAT and CHO compared with the same test at thermal neutrality (p < 0.05). As expected, cold increased plasma glucose R and plasma FFA R (from 4.58 ± 0.19 to 14.69 ± 1.07 µmol·kg-1·min-1; p < 0.05). However, in absolute terms, plasma FFA R in the cold remained more than twice greater than FAT (FAT only increased up to 6.9 ± 0.85 µmol·kg-1·min-1), suggesting an enhanced non-oxidative disposal of fatty acids (i.e., TG/FFA cycling) to account for all FFA R. Indeed, cold increased extracellular TG/FFA recycling rate (2.23 ± 0.40 vs 7.77 ± 1.19 µmol·kg-1·min-1; p < 0.05) whereas intracellular cycling was unaffected. Conclusion: Even though lipolysis and FFA R are greatly increased by cold stress in humans, the present results demonstrate that only about half the rate of FFA R is ultimately oxidized, suggesting that under the present cold conditions: 1) non-oxidative FFA disposal or TG/FFA cycling is significantly enhanced; 2) white adipose tissue-derived fatty acids could easily account for most of FAT. The results further emphasize the importance of the TG/FFA cycle in amplifying the ability of stored TG to react quickly to major changes in energy expenditure induced by a sustained cold stress.Keywords: body temperatures, energy metabolism, energy substrates, glycerol, heat balance, heat loss, heat production, non-oxidative disposal, shivering, stable isotope. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 70, Number 1 of the ASME journal.
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