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

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Abstract
Rats were maintained at 24.degree. C (WA; warm-adapted) or 4.degree. C (CA; cold-adapted) and fed a pelleted stock diet (WAS, CAS) or a varied and palatable cafeteria diet (WAC, CAC). Resting O2 consumption (.ovrhdot.VO2, 29.degree. C) was significantly elevated by 15, 14 and 24% in WAC, CAS and CAC rats, respectively, compared with WAS controls. These differences were completely abolished by injection of propranolol in all but CAC rats, where .ovrhdot.VO2 remained slightly elevated. Experimental groups showed an increased capacity to respond to the thermogenic effects of norepinephrine (percentage increase in .ovrhdot.VO2: WAS, 43 .+-. 5; WAC, 88 .+-. 6; CAS, 75 .+-. 6; CAC, 128 .+-. 5) and greater 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.degree. 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.degree. C; WAC, 36.2 .+-. 0.5.degree. 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 and in energy-balance regulation.