O’CONNOR, T.P.; SCHULTERS, R.; ANDZIAK, B.A.; PIERCE, V.A.: Effect of cold-acclimation on metabolism, body composition and glycolytic enzymes in mice

Both acute and chronic cold exposure result in increased metabolic rate in endotherms, as they try to maintain their body temperature. Increased metabolic rates, both chronic and acute, are produced by increased flux through catabolic pathways such as glycolysis. We used cold-acclimation to increase the daily energy expenditure of lab mice (Mus musculus) and then examined the effects on basal and maximal metabolic rate (BMR and MMR, respectively), body composition, and glycolytic enzymes. Cold-acclimated (CA) mice were maintained at 4°C, and warm-acclimated (WA) mice at 23°C, for 6-8 wks. MMR was measured using exposure to cold temperature in a helium-oxygen system. Body composition was assessed before and after acclimation using dual x-ray absorptiometry. We used microplate spectrophotometry to measure the activity of all glycolytic enzymes except hexokinase in the gastrocnemius muscle. There were no differences in body mass or body composition between the two groups of mice prior to acclimation. Following acclimation, CA mice had a 60% greater BMR and a 47% greater MMR than WA mice. Body mass of both groups increased 50% during acclimation. Body fat remained unchanged at 14% of body mass for CA mice, but doubled to 28% of body mass during acclimation in WA mice. Our preliminary data showed trends for increased activities of several glycolytic enzymes in CA mice compared to WA mice, but none were significant given our pilot sample sizes. Not surprisingly, the increase in BMR and MMR in CA mice was associated with an increased ratio of lean mass to fat mass. Conclusions regarding the specific glycolytic adjustments associated with increased metabolism require additional investigation.