Effects of fasting and refeeding on energetic metabolism of cold acclimated rats

In rats acclimated at 5°C or 28°C (thermal neutrality), overnight fasting induced decreases in body and brown adipose tissue (BAT) weights and led to a larger decrease in resting metabolism (RM) in the 5°C rats than in the 28°C group. Refeeding significantly enhanced RM (diet-induced thermogenesis) in a greater extent in 5°C than in 28°C rats. This effect was inhibited by propranolol (β adrenergic receptor antagonist) in 28°C but was only halved in 5°C rats. The capacity for nonshivering thermogenesis as determined by norepinephrine infusion was reduced by fasting only in 28°C group; it remained unchanged in cold acclimated rats despite the large lipid utilization induced by fasting.