Fuel selection in Wistar rats exposed to cold: shivering thermogenesis diverts fatty acids from re-esterification to oxidation

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Blackwell Science Inc

RESUMO

This study characterizes the effects of shivering thermogenesis on metabolic fuel selection in Wistar rats. Because lipids account for most of the heat produced, we have investigated: (1) whether the rate of appearance of non-esterified fatty acids (Ra NEFAs) is stimulated by shivering, (2) whether mono-unsaturated (oleate) and saturated fatty acids (palmitate) are affected similarly, and (3) whether the partitioning between fatty acid oxidation and re-esterification is altered by cold exposure. Fuel oxidation was measured by indirect calorimetry and fatty acid mobilization by continuous infusion of 9,10-[3H]oleate and 1-[14C]palmitate. During steady-state cold exposure, results show that total heat production is unequally shared by the oxidation of lipids (52% of metabolic rate), carbohydrates (35%) and proteins (13%), and that the same fuel selection pattern is observed at all shivering intensities. All previous research shows that mammals stimulate Ra NEFA to support exercise or shivering. In contrast, results reveal that the Ra NEFA of the rat remains constant during cold exposure (∼55 μmol kg−1 min−1). No preferential use of mono-unsaturated over saturated fatty acids could be demonstrated. The rat decreases its rate of fatty acid re-esterification from 48.4 ± 6.4 to 19.6 ± 6.3 μmol kg−1 min−1 to provide energy to shivering muscles. This study is the first to show that mammals do not only increase fatty acid availability for oxidation by stimulating Ra NEFA. Reallocation of fatty acids from re-esterification to oxidation is a novel, alternative strategy used by the rat to support shivering.

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