Effects of diet and obesity on brown adipose metabolism.

The effect of diet-induced obesity on interscapular brown adipose tissue (IBAT) was assessed after feeding male Sprague-Dawley rats a high-fat diet for 3-5 mo beginning at 3 mo of age. IBAT pads in 6-mo-old obese rats were heavier (22%), had more lipid (71%), and larger unilocular cells (38%) than chow-fed controls. Mitochondrial morphology, beta-adrenergic receptor binding ([ 125I]iodocyanopindolol), and norepinephrine-stimulated lipolysis were similar in IBAT from obese and control rats. When 8-mo-old chow-fed rats were switched to the high-fat diet for 7-14 days, IBAT pads became hypercellular without cell hypertrophy and with a 70% increase in norepinephrine-induced lipolysis. However, when 8-mo-old obese rats that had been on the high-fat diet for 5 mo were switched to chow for 3 days, IBAT cellularity was unchanged, but norepinephrine-induced lipolysis was increased 70%. Therefore, in lean and obese 6- to 8-mo-old rats, short-term dietary manipulation led to metabolic activation, whereas chronic diet-induced obesity on a stable diet was associated with a return of IBAT metabolism to control levels.