VAILLANCOURT, E.; HAMAN, F.; WEBER, J.-M.; University of Ottawa, Ottawa; University of Ottawa, Ottawa; University of Ottawa, Ottawa: Relative use of lipids and carbohydrates during prolonged cold exposure.

The effects of cold exposure on total energy expenditure have been well characterized, but the relative importance of the different metabolic fuels is not known. Our goal was to quantify oxidative fuel selection during prolonged shivering of different intensities. The rates of oxygen consumption (VO₂) and CO₂ production (VCO₂) of 27&degC-acclimated rats were measured while they were exposed to 15, 10, or 5&degC for 3 h. Rates of lipid and carbohydrate oxidation were calculated from VO₂ and VCO₂, assuming a constant contribution from protein oxidation. We found that carbohydrate oxidation played a dominant role during the first hour of shivering, but its relative importance then declined progressively and this gradual shortfall was compensated for by a reciprocal increase in lipid oxidation at all temperatures. Surprisingly, changes in the relative importance of lipids and carbohydrates followed the same pattern for all shivering intensities during the last 2 h of cold exposure. Moreover, lipid oxidation was responsible for more than 50% of VO₂ during the last hour at all temperatures. We conclude that, after shivering for 2 h, heat production is unequally shared between lipid, carbohydrate and protein oxidation, and this partitioning between oxidative fuels is independent of shivering intensity. After prolonged cold exposure, lipids account for the production of more heat than all other fuels combined, even under conditions of intense shivering. Therefore, future studies of prolonged, cold-induced thermogenesis in rodents should focus on the mechanisms responsible for mobilization, transport and oxidation of lipid reserves. This work was supported by an NSERC grant to J.-M. Weber.