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Dietary Branched-Chain Amino Acids and Protein Selection by Rats^1,2,3,

Departments of Biochemistry and Nutritional Sciences, University of Wisconsin-Madison 53706

Consumption by rats of high protein diets is associated with elevated plasma and brain concentrations of branched-chain amino acids (BCAA). We examined the possibility that changes in BCAA concentrations in blood and brain might serve as modulators of protein consumption. After young rats had adjusted to selecting between a 10% or 25% casein diet and a 50% casein diet, a mixture of BCAA was included in the diet containing the lower amount of protein (10% + BCAA, 25% + BCAA). Supplementation of the 10% or 25% casein diets with BCAA and subsequent elevation of BCAA concentrations in plasma and brain were associated with increased selection of protein in rats given the 10% + BCAA/50% casein diet choice, but not in rats offered the 25% + BCAA/50% casein diets. When no alternative diet was available, addition of BCAA to a 15% casein diet depressed food intake, and rats given a choice between a 15% casein diet with or without added BCAA selected almost exclusively the diet without added BCAA. Although BCAA concentrations were high in plasma and brain in all experiments, concentrations of methionine, tyrosine, phenylalanine, tryptophan and histidine were low in brain in experiments in which rats altered their diet or protein selection after BCAA addition. High concentrations of BCAA in plasma and brain were not consistently associated with changes in protein selection.

KEY WORDS: • branched-chain amino acids • food intake • large neutral amino acids • protein selection • rats

¹ Supported in part by grants AM10747 and DK10747 from the National Institutes of Health.

² Presented in part at the 71st Annual Meeting of the Federation of American Societies for Experimental Biology, April 2, 1987, in Washington, D.C. [ANDERSON, S. A., TEWS, J. K. & HARPER, A. E. (1987) Intake of diets with added branched-chain amino acids is influenced by alternative diets. Fed. Proc. 46: A1483 (abs. 6809)].

³ Reprints are not available.

Manuscript received 31 January 1989. Revision accepted 21 September 1989.