Metabolic and sympathetic nerve activities of brown adipose tissue in tube-fed rats

Abstract

To investigate possible contribution of oropharyngeal factors to thermogenesis in brown adipose tissue (BAT), rats were given a liquid diet orally or through a gastric tube for 4-12 days. Tube-fed rats weighed more and had heavier white adipose tissue than orally fed rats, although they were given the same amount of the diet. Triglyceride content of the interscapular BAT was higher in tube-fed rats, but the rate of fatty acid synthesis was lower than those in orally fed rats. Uptake of 2-deoxyglucose (2DG), an index of glucose utilization, in BAT was also lower in tube-fed rats. Surgical sympathetic denervation of BAT reduced both lipogenic activity and 2DG uptake to abolish the differences in these metabolic activities between tube-fed and orally fed rats. Sympathetic nerve activity in the BAT assessed from the turnover rate of norepinephrine in the tissue was lower in tube-fed rats. The results suggest that there is a sympathetically mediated mechanism dependent on afferent input from oropharyngeal receptors to regulate BAT thermogenesis and that greater fattening seen after tube feeding may be attributable to a decreased BAT thermogenesis because of the absence of food-induced sensory stimulation.