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Effect of Dietary Linoleic Acid and Essential Fatty Acid Deficiency on Resting Metabolism, Nonshivering Thermogenesis and Brown Adipose Tissue in the Rat¹

Institut für Biochemie I der Universität Heidelberg, Im Neuenheimer Feld 328, D-6900 Heidelberg, West Germany

Rats were fed a diet either deficient (0.05%) in essential fatty acids (EFA), or providing 4% (control) and 10% (surplus) of the total energy intake in the form of linoleic acid. All diets were isoenergetic and provided 13.9% of the energy as fat. The rats were kept at 29 or 5°C. Growth and food intake of rats fed linoleic acid surplus at either temperature for 10 wk were not different from that of controls; basal metabolism, norepinephrine-induced nonshivering thermogenesis (NST) and thermogenic variables in the brown adipose tissue (amount of mitochondria and mitochondria uncoupling protein) also were not different. The effects of EFA deficiency were drastically enhanced in the cold: After 10 wk of consuming a diet low in EFA at 5°C, the body weight of rats was 75% of that of controls (87% at 29°C); the food intake was 135% of controls at 5°C (120% at 29°C). The resting respiration in deficient rats was 125% of controls at 5°C (110% at 29°C); body temperatures as low as 35.1°C were measured in deficient rats after 3 wk at 5°C; the cold tolerance of the rats was significantly diminished (30% died within 3 wk at 5°C), thus emphasizing the essential role of dietary EFA during cold stress. Norepinephrine-induced NST and the thermogenic parameters in brown fat were not influenced by EFA deficiency. It is concluded that the amount of EFA has no influence on the modulation of NST capacity in rats as observed in earlier experiments in which the level of dietary triglycerides was varied.

KEY WORDS: • linoleic acid • essential fatty acid deficiency • nonshivering thermogenesis • brown adipose tissue

¹ Supported in part by a grant from the Deutsche Forschungsgemeinschaft.

² Permanent address: Institut für Ernährungwissenschaft der Universität Giessen, Wilhelmstrasse 19, D-6300 Giessen, FRG.

Manuscript received 31 March 1987. Revision accepted 4 January 1988.

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