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Studies in Amino Acid Utilization

III. The Role of the Indispensable Amino Acids in Maintenance of the Adult Albino Rat¹

One Figure

Department of Pathology, University of Chicago, Illinois

The qualitative amino acid requirements for maintenance of the normal adult male rat have been measured using the criteria of preservation of appetite and weight as well as nitrogen balance. A purified amino acid mixture patterned after the composition of casein served as the source of dietary nitrogen in the basal ration. The effects upon appetite and weight following removal of each of the 9 essential amino acids and all of the non-essential amino acids have been observed, as well as the effects of substituting norleucine for leucine or lysine and tyrosine for phenylalanine. When single amino acid deficiencies were studied, pairs of comparable rats, one receiving the complete ration and one the incomplete, were used. In some instances these rations were interchanged at the end of the first 20 days and the experiment was continued for an additional 10 days. Nitrogen balance determinations were made in representative animals during the first 14 days of the experiment, two 7-day collection periods serving as mutual checks. In 1 experiment the force-feeding technique was used to equalize the nitrogen and caloric intakes between the deficient and control rats.

The results may be summarized as follows:

1. The normal adult rat maintains appetite and weight when receiving rations in which only the 10 amino acids essential for growth are present.

2. The removal of arginine from this mixture produces a variable depression of appetite. When appetite is maintained, weight and a positive nitrogen balance are preserved.

3. The absence of each of the remaining 9 essential amino acids from the basal ration, although producing a variable depression in appetite, always leads to weight loss and a negative nitrogen balance. The absence of tryptophane, methionine and threonine does not produce the marked loss of appetite observed with the same deficiencies in the protein-depleted rat. The absence of lysine led to only slight interference with voluntary food consumption in both the protein-depleted and normal adult rat. In most instances the effect on food consumption was not quite so acute or marked as that observed previously in the protein-depleted rat.

4. Substitution of norleucine for leucine or lysine led to decreased appetite and weight loss similar to those produced by a deficiency of these amino acids. Substitution of tyrosine for phenylalanine resulted in a loss of appetite and weight somewhat less severe than that produced by phenylalanine deficiency.

5. Despite equalization of the food intakes of the rats deficient in lysine, leucine, histidine and phenylalanine with their controls by means of the force-feeding technique the animals on deficient rations lost weight and were in negative nitrogen balance.

6. Our results indicate that the same 9 essential amino acids required for growth of the young rat are necessary for maintenance of appetite, weight and nitrogen balance in the adult rat.

The work has been aided, also, by The National Livestock and Meat Board, The Douglas Smith Foundation for Medical Research of The University of Chicago, and the Allen B. Wrisley Company.

Manuscript received 25 March 1948.