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Food Intake, Growth and Tissue Amino Acids in Rats Fed Amino Acid Analogues¹

Departments of Biochemistry and Nutritional Sciences, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI 53706

The objective of this study was to examine the effects of dietary additions of analogues of large neutral amino acids (LNAA), previously shown to inhibit entry of natural LNAA into brain, on food intake, growth and tissue concentrations of specific amino acids in young rats. A mixture of norleucine, norvaline, -amino-phenylacetate and -aminooctanoate (atypical amino acids, AAA) markedly depressed food intake and growth of rats fed a 6% protein diet (LP) for 10 d but not of rats fed a 50% protein diet (HP). Except in rats fed HP, dietary AAA usually decreased concentrations of LNAA more than of small neutral amino acids (SNAA) or lysine, especially in brain. Concentrations of LNAA, especially in brain and muscle of rats adapted to LP or HP meals and fed one LP-AAA meal were lower than in similar rats fed one LP meal without AAA; feeding an HP-AAA meal to such rats generally prevented or lessened these changes. AAA-induced changes in SNAA and lysine were usually small in meal-fed rats. When AAA induced decreases in LNAA, the branched-chain amino acids were usually most affected; valine and isoleucine sometimes were undetected in brain and muscle. Serotonin and dopamine concentrations were not low in brain despite low levels of tryptophan and tyrosine. Changes in tissue LNAA concentrations would appear to reflect in part competition by large neutral AAA for transport of natural LNAA from the blood.

KEY WORDS: • amino acid transport • brain • dietary protein • liver • muscle • neurotransmitters • plasma

¹ Supported in part by the College of Agricultural and Life Sciences at the University of Wisconsin-Madison and by grant AM 10747 from the National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases of the National Institutes of Health, Bethesda, Maryland.

Manuscript received 3 January 1985. Revision accepted 31 May 1985.