ENDOGENOUS FLOW OF TOTAL LYSINE AND OTHER AMINO-ACIDS AT THE DISTAL ILEUM OF THE PROTEIN-FED OR PEPTIDE-FED RAT - THE CHEMICAL LABELING OF GELATIN PROTEIN BY TRANSFORMATION OF LYSINE TO HOMOARGININE

Endogenous total lysine flow at the distal ileum was determined directly with seven 200‐g male rats fed a gelatin‐based diet in which all the lysine had been transformed to homoarginine. The latter lysine flow was compared with one determined indirectly with seven rats given a partially guamdinated gelatin‐based diet. There was no significant difference (P > 0.05) between the direct (469 ± 27.9 μg g−l freeze dry matter intake (FDMI);x̄ ± SE) and indirect (506 ± 44.2 μg g−1 FDMI) estimates. The overall mean endogenous lysine flow for the 14 rats receiving the guamdinated gelatin‐based diets was compared with flows determined with six rats given a diet the sole nitrogen source of which was enzyme hydrolysed casein (EHC) and six rats fed a protein‐free diet. The EHC, a mixture of free amino acids and oligopeptides, was assumed to be completely digested and absorbed by the end of the small intestine of the rat. The mean flow of lysine for the EHC‐fed rats(522 ± 24.8 μg g−l FDMI) was not significantly different (P > 0.05) from that for the rats given the guanidinated gelatin‐based diets, but the flow for those on the protein‐free diet was significantly lower (238 ± 9.4 μg g−l FDMI). The endogenous flows of the amino acids other than lysine for the EHC‐fed rats, were higher (P < 0.05) than values found for rats on the protein‐free diet, except for glycine where there was no significant difference. It was concluded that there is a direct effect of dietary protein and peptides on the net loss of endogenous lysine and other amino acids from the small intestine of the growing rat. Endogenous amino acid flow at the terminal ileum may be underestimated when measurement is made using the traditional protein‐free method. Copyright © 1990 John Wiley & Sons, Ltd