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High Fat Feeding Increases Brown Fat GDP Binding In Lean but not Obese Zucker Rats¹

T. W. Linda Gong^*, Judith S. Stern^*,,2 and Barbara H. Horwitz^**

^* Department of Nutrition ^** Animal Physiology Division of Clinical Nutrition, Department of Internal Medicine; and Food Intake Laboratory, University of California, Davis, CA 95616

The effects of high fat feeding on brown fat thermogenesis in rodents are controversial. In this study, we examined the effects of 8 d of high fat feeding on brown fat mitochondrial GDP binding (an in vitro index of thermogenic activity) in lean (Fa/?) and obese (fa/fa) Zucker rats. Six-week-old female rats were fed a defined low fat control diet (9.5% of energy from fat) only during the dark cycle (1200–2400 h), and food intake was measured daily at 1200, 1600, 2300, and 2400 h for 7 d (the control period). For the next 8 d, half of the lean and obese rats were fed a high fat diet (65% of energy from fat), and the others remained on the low fat control diet. Each rat was fed the amount of energy equivalent to its average energy intake during the 7-d control period. Rats were killed at 0800–1000 h. In the lean rats, high fat feeding increased GDP binding. This increased binding in the lean rats appeared to reflect levels of dietary fat and carbohydrate and was independent of caloric intake. The blunted GDP binding of the obese rats failed to respond to dietary changes.

KEY WORDS: • brown fat • mitochondria • thermogenesis • GDP binding • Zucker rats

¹ This research was supported in part by NIH grants DK-18899, DK-32907 and P32 DK35747.

² Address correspondence to Dr. Judith S. Stern, Department of Nutrition, University of California, Davis, CA 95616.

Manuscript received 23 August 1989. Revision accepted 13 December 1989.