Similarities between cold- and diet-induced thermogenesis in the rat

Abstract

Rats were maintained at 24 and 4 °C (WA, CA) and fed either a pelleted stock diet (WAS, CAS) or a varied and palatable cafeteria diet (WAC, CAC). Resting oxygen consumption ([Formula: see text], 29 °C) was significantly elevated by 15, 14, and 24% in WAC, CAS, and CAC rats, respectively, compared with WAS controls and these differences were completely abolished by injection of propranolol in all but CAC rats, where [Formula: see text] remained only slightly elevated. Experimental groups showed an increased capacity to respond to the thermogenic effects of norepinephrine (percentage increase in [Formula: see text]: WAS, 43 ± 5; WAC, 88 ± 6; CAS, 75 ± 6; CAC, 128 ± 5) and greather deposits of interscapular brown adipose tissue (IBAT) (WAC, 542 ± 27; CAS, 469 ± 27; CAC, 1111 ± 85 mg) compared with WAS controls (339 ± 22 mg).When exposed to 5 °C, WAS rats shivered continuously whereas in the WAC animals shivering had ceased by 5 h. Rectal temperature was maintained at a higher level in the WAC rats than in the WAS group (WAS, 34.7 ± 0.9 °C; WAC, 36.2 ± 0.5 °C; p < 0.01). Injection of propranolol lowered the core temperature of WAC rats and caused shivering to recommence but had no effect on WAS rats.The similarities between diet- and cold-induced thermogenesis suggest that both have a common metabolic origin residing in BAT and that dietary-induced thermogenesis may be important in the maintenance of body temperature as well as in energy balance regulation.