THE ROLE OF THE AUTONOMIC NERVOUS-SYSTEM IN THE THERMAL EFFECTS OF PROTEIN AND CARBOHYDRATES IN RATS

To investigate the roles of the autonomic nervous system in the thermi c effects of protein and carbohydrates in rats,we determined the urina ry excretion of catecholamines and the resting oxygen consumption by m eans of HPLC-fluorometry and open-circuit respirometry, respectively. Protein administration significantly increased the urinary excretion o f norepinephrine and epinephrine over those on water administration. T he thermic effect of protein was 16.6% of the basal metabolic rate and was inhibited by phentolamine, prazosin, or atropine, but not by prop ranolol. These results suggest that the sympathetic nervous system via al-adrenoceptors and the parasympathetic nervous system are involved in the thermic effect of protein. The administration of carbohydrates such as glucose, sucrose, and fructose significantly enhanced the urin ary excretion of norepinephrine, but only glucose administration incre ased the urinary excretion of epinephrine. The thermic effects of carb ohydrates were 8-9% of the basal metabolic rate and were inhibited by propranolol, but not by phentolamine or atropine. These findings sugge st that the sympathetic nervous system via P-adrenoceptors, but not th e parasympathetic nervous system, contributes to the thermic effect of carbohydrates. Thus, we conclude that the autonomic nervous system is involved in the thermic effects of protein and carbohydrates by diffe rent mechanisms.