Norepinephrine turnover in brown adipose tissue is stimulated by a single meal

A single meal stimulates brown adipose tissue (BAT) thermogenesis in rats. In the present study the role of norepinephrine in this thermogenic response was assessed from the rate of its turnover in BAT after a single test meal. For comparison, norepinephrine turnover was determined in the heart and spleen. A total of 48 male Wistar rats (200 g) were trained to eat during two feeding sessions per day. On the experimental day, one group (n = 24) was meal deprived and the other (n = 24) was given a low-protein high-carbohydrate test meal for 2 h. The synthesis inhibition method with alpha-methyl-p-tyrosine was employed to determine norepinephrine turnover from its concentration at four hourly time points after the meal. Tissue concentrations of norepinephrine were determined by radioimmunoassay. Norepinephrine concentration and turnover rate were increased more than threefold in BAT of the meal-fed compared with the meal-deprived rats (P less than 0.001 and P less than 0.005 for concentration and turnover, respectively). Neither were significantly altered by the meal in the heart or spleen. Other measures of turnover kinetics, turnover time and rate constant, were not significantly affected in any of the tissues examined. Our data suggest that norepinephrine mediates a portion of the thermic effect of meals that originate in BAT.