Stearic acid oxidation in the Alaskan red-backed vole: effects of cold and norepinephrine

Saturated fatty acids constitute a considerable energy reserve that could convey survival value under chronic cold exposure. It was investigated whether acclimation to cold was associated with a change in the ability of a small microtine rodent, the red-backed vole (Clethrionomys rutilis), to increase the use of saturated fatty acids during thermogenesis. The C-14 labeled stearic acid, a typical saturated fatty acid (FA), was used to determine the rate of utilization through oxidation. In warm acclimated (WA, 20 degrees C) and cold acclimated (CA, 5 degrees C) voles, acute cold exposure (WA at 5 degrees C, -2 degrees; CA at -5 degrees C) and norepinephrine (NE) injection increased metabolic rate (VO2, VCO2) and mobilization of lipid reserves. Acute cold exposure increased percent blood stearate oxidized in a linear fashion with both metabolic rate and stearate concentration in both WA and CA voles. The CA voles at 5 degrees C had increased stearate irreversible loss (1.5x) and oxidation rate (2x) compared to WA voles at 20 degrees C. The CA voles at -5 degrees C increased stearate irreversible loss and oxidation linearly with metabolic rate and blood stearate concentration. In CA voles the contribution made by stearate oxidation to VCO2, increased with the level of cold exposure and NE injection. In contrast, for WA voles stearate irreversible loss and the contribution made by stearate oxidation to VCO2 were unaffected by acute cold exposure. Thus, cold acclimation involves: (1) a modest increase (1.5x) in the use of stearate as a fuel substrate; and (2) a greater stearate oxidation and contribution to overall metabolism during acute cold exposure (-5 degrees C).