1. Changes in the serum amino acid ratio have been compared with alterations in liver
composition in young rats growing on three different diets, control, low-protein and ‘undernourished’. The rate of growth in the latter group was controlled to be the same as in the low-protein animals.
2. The amino acid ratio only became elevated in the protein-deficient animals but not to
the degree found in protein-malnourished children.
3. Protein/g DNA was lost from the livers of the protein-deficient rats and this occurred at the same time as the serum amino acid ratio rose. The possibility that the two phenomena might be linked is discussed. Protein loss from the liver was not a feature in the undernourished animals.
4. Reduced serum total protein and albumin concentrations also developed in the rats fed
the low-protein diet and this occurred as the amino acid ratio started to rise.
5. The liver did not become fatty in the low-protein animals until after the amino acid ratio had reached its maximal value. It was concluded, therefore, that the distorted pattern of serum amino acids could not be a result of this pathological condition.
6. There was no apparent relationship between liver RNA levels and the magnitude of the
serum amino acid ratio.
7. The limitations of the rat as animal model for the study of chronic protein malnutrition in early childhood are discussed.