Cold acclimation of obese ( [formula omitted]) mice: Effects on skeletal muscle and bone

Abstract

Obese ( ob ob ) and lean mice at 4 weeks of age were housed at 23 °C or 14 °C for 4 or 8 weeks to determine effects of acclimation to mild cold on the growth of skeletal muscle, bone, and fat. Body weights at 12 weeks of age averaged 48 ± 0.6 g and 27 ± 1.9 g for obese mice housed at 23 °C and 14 °C and 29 ± 0.5 g and 26 ± 0.6 g for lean mice housed at 23 °C and 14 °C, respectively. At 23 °C, muscle weights of obese mice were approximately 60% of those in lean mice. Muscles of obese mice did not grow during the first 4 weeks at 14 °C (4 to 8 weeks of age) but did show a small gain during the second 4 weeks (9 to 12 weeks of age) at 14 °C. As a result, by the end of 8 weeks at 14 °C, muscles of obese mice weighed only 35% to 45% as much as muscles of lean mice. Growth of the tibia and femur followed the same pattern as the muscles. Obese mice housed at 23 °C from 4 to 12 weeks of age contained about six times as much fat as lean mice at this age. Although exposure to 14 °C for 8 weeks depressed the accumulation of fat in obese mice, they still contained approximately three times the percentage body fat as lean counterparts. The concentrations of corticosterone and insulin in plasma of 8 week old obese mice housed at 23 °C were two to four times and 20 times higher, respectively, than in lean mice; after 4 weeks at 14 °C the difference for corticosterone was even greater, ie, five to ten times higher in 8 week old obese, whereas the concentration of insulin in plasma of obese mice was only seven times higher than in lean mice at 14 °C. The marked reduction in skeletal muscle and bone growth observed in young obese mice as a result of cold acclimation permitted them to decrease body weight gain to equal that of lean mice without a concomitant reduction in their high percentage of body fat. These cold-induced reductions in muscle and bone growth in obese mice may have been facilitated by the observed changes in plasma corticosterone levels.