| Abstract: | In a comparative study endogenous amino acid flow was determined in twenty-four 190-g male rats (protein-replete) given diets containing synthetic amino acids as the sole nitrogen source but devoid of specific amino acids, and six rats fed a protein-free diet. Endogenous flows were not significantly different (P > 0.05) for aspartic acid, glutamic acid, serine and lysine but were significantly higher (P < 0.05) under protein-free alimentation than amino acid alimentation for proline, glycine and alanine. This indicates that the protein-free method did not lead to lowered endogenous amino acid excretions owing to an altered amino acid metabolism in the protein-free state. The loss of some amino acids may be enhanced under protein-free alimentation. The high apparent digestibility of the synthetic amino acids not excluded from the diets (histidine, arginine, threonine, valine, isoleucine, leucine, tyrosine, phenylalanine) indicated that their ileal excretions were mainly of endogenous origin. There were no significant differences (P>0.05) between the latter excretions and those obtained by feeding the rats a protein-free diet. |
