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Muscle Respiration in Rats Is Influenced by the Type and Level of Dietary Fat^1,2,3,

Department of Animal Sciences, University of Hawaii at Manoa, Honolulu, HI 96822

Experiments were conducted to elucidate the role of muscle in the enhanced thermogenic response found in rats fed diets enriched with polyunsaturated fatty acids. Isolated soleus muscle respiration and plasma cholesterol and triglyceride concentrations were determined in rats (128 g wt, 5 wk age) fed diets (minimum 3 wk) containing coconut oil, beef tallow or safflower oil at 20, 40 or 60% of the total dietary energy in a 3 x 3 factorial design (5–6 rats per treatment). Diet type did not affect plasma cholesterol concentrations but plasma triglycerides were lower (P < 0.01) in rats fed safflower oil-based diets. Greater levels of fat in the diet resulted in higher (P < 0.01) plasma cholesterol concentrations and lower (P < 0.01) plasma triglyceride concentrations. Rats fed coconut oil had lower (P < 0.05) rates of soleus muscle respiration compared with rats fed the other two diets. This lower respiration rate was not related to changes in protein synthesis (cycloheximide-sensitive respiration). However, this change may partially be related to enhanced Na⁺,K⁺ transport (ouabain-sensitive respiration). The results indicate that muscle is partially responsible for the enhanced thermogenic response found in rats fed diets enriched with polyunsaturated fatty acids and that enhanced ion transport contributes to this response in muscle.

KEY WORDS: • fatty acids • muscle • rats • energy expenditure • Na⁺,K⁺ ATPase

¹ Supported by a University of Hawaii Research and Training Revolving Fund Seed-Money Award from the University Research Council.

² This is Hawaii Institute of Tropical Agriculture and Human Resources journal series no. 4004.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence and reprint requests should be addressed.

Manuscript received 14 February 1994. Revision accepted 3 January 1995.