Studies of amino acid requirements of adult rats

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Abstract
1. A series of experiments was carried out to determine the minimum essential amino acid requirements of the adult rat.2. After testing four amino acid patterns taken from the literature, a basal pattern was formulated in which each amino acid appeared at the lowest level at which it was presented in any of the original diets.3. Nitrogen balance was the main criterion used to judge any benefit arising from modest increases in individual amino acids tested in a modified Latin-square design. They were given at a protein level of 3.6% of the diet. Non-essential amino acids were in the same proportions as in whole egg.4. It appeared that three amino acids, namely tryptophan, threonine and isoleucine, brought about more favourable balances when presented at concentrations higher than basal.5. Reduced levels of each amino acid were then tested in order to ensure that no surpluses were present.6. N retentions indicated that lysine, phenylalanine plus tyrosine, leucine and valine could be reduced below the basal level and still meet the needs of the rat for these amino acids.7. When the pattern of amino acids arising from these latter trials was tested in combination, rather than as trios, pairs, or single changes, positive N balances gave confidence that these were minimal levels of the essential amino acids required for meeting the maintenance needs of adult rats.8. Plasma proteins from the rats on the evolved pattern were found to be in no way different from those found for normal animals. This gave further support to the belief that the pattern was adequate for the rats.