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Amino Acid Balance and Imbalance

VII. Effects of Dietary Additions of Amino Acids on Food Intake and Blood Urea Concentration of Rats Fed Low-Protein Diets Containing Fibrin¹

Department of Biochemistry, University of Wisconsin, Madison, Wisconsin

The low food intake of rats fed a diet containing 6% of fibrin supplemented with methionine and phenylalanine does not seem to be associated with a slower rate of stomach emptying. Feeding this imbalanced diet failed to reduce the ability of the rat to synthesize the enzyme tryptophan pyrrolase in response to a test dose of tryptophan.

The blood urea concentration of rats was greatly elevated three hours after the rats had ingested diets supplemented with mixtures of methionine and phenylalanine or arginine and threonine, both of which cause amino acid imbalance which result in depressions in growth and food intake. The rise in blood urea concentration was prevented by the further addition of the amino acids needed to correct the imbalance—leucine, isoleucine, valine and histidine.

Food intake was not depressed nor was blood urea concentration increased when mixtures of amino acids that do not cause growth depressions were included in the diet.

Several pairs of amino acids that caused depressions in growth and food intake did not cause a rise in blood urea concentration such as that observed in animals receiving methionine and phenylalanine.

Daily injections of insulin stimulated the growth and food intake of rats fed a diet containing 6% of fibrin supplemented with methionine and phenylalanine.

Manuscript received 25 November 1960.