[Improved thermogenesis during acute cold exposure in exercise-trained rats].

The present study was carried out to examine the effects of enhanced cold tolerance induced by exercise training on carbohydrate metabolism during cold exposure. Five-week-old male Wistar rats were divided into three groups. The warm-acclimated control group (WA) was exposed to the environment at 25 degrees C, and the cold-acclimated group (CA) was acclimated to cold by exposure to 5 degrees C. The exercise-trained group (ET) was controlled to run at the rate of 35 meters per minute for 9 weeks on a small driven treadmill. The degree of carbohydrate metabolism due to cold exposure significantly decreased with the drop in environmental temperature in the WA and CA groups, but did not change in the ET group. When glucose utilization was blocked with 2-deoxyglucose administration, oxygen consumption during cold exposure decreased in the WA and ET groups, but did not decrease in the CA group. The liver glycogen content decreased during cold exposure in the WA and ET groups, but there was no change in the CA group. It appeared that the fall of the plasma glucose level after the infusion of insulin was significantly greater in the ET and CA groups than in the WA group. These results indicate that the improved capacity for cold-induced thermogenesis in the ET group may be caused by enhanced carbohydrate metabolism.