Maintaining thermogenesis during cold exposure in humans: relying on multiple pathways

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Through evolution, humans have acquired efficient metabolic and physiological defenses to dissipate heat in warm climates. However, their furless bodies do little to prevent excessive heat loss in cold environments. In the cold, humans must rely on the concerted activation of physiological processes that increase Hprod and lower heat loss (Hloss). When exercise is not possible, the increase in Hprod is achieved involuntarily by the activation of ST and to a lesser extent by NST. By combining metabolic, isotopic, biochemical and electrophysiological approaches, the long-term objective of the proposed research program is to better understand the mechanisms that regulate and maintain thermogenenic processes in humans exposed to adverse environments. Currently, it focuses on three main areas of research: 1) Effects of cold acclimation on thermogenic processes, 2) The partitioning of energy reserves for sustaining thermogenic processes during acute cold exposure, 3) The metabolic and neuromuscular principles that govern muscle activity in the cold. These overall questions constitute the continuation of previous experiments conducted for the last 10 y in my laboratory. They will advance the current knowledge by focusing on long duration acute cold exposure in non cold acclimatized subjects and on the effects of various cold acclimation levels of thermogenic processes. Building on our previous studies, the proposed work will quantify: 1) the effects of intense cold acclimation on the respective contributions of ST and NST to Hprod, 2) the changes in plasma glucose, muscle glycogen, CHO, lipid and protein oxidation during long duration cold exposure, 3) the effects of long duration cold exposure and cold acclimation on ST pattern.***Building on the knowledge gained in the last ten years of NSERC funding, the proposed experiments will include the combination indirect calorimetry, whole body metabolic tracer and electromyographic methodologies developed in the applicant laboratory. However, to better understand the metabolic requirements of individual tissues in cold exposed adult humans and the metabolic requirements of shivering muscles. These combined techniques will allow the applicant and his trainees to establish more clearly the factors that modulate the relative use of metabolic fuels and the relative contribution of ST and NST. Results from this research program, together with the novel experimental approach, will expand on previous work funded by NSERC and provide novel information for shivering research. It will help achieve the long term objective of improving the characterization of the metabolic basis of shivering in humans.