Portal absorption of small peptides in rats under unrestrained conditions.

The intestinal absorption of small peptides was investigated in rats under unrestrained conditions. The peptide utilized in the experiment was hydrolysate of egg white protein with an average molecular weight of about 350 and containing less than 10% of free amino acids. We compared the intestinal absorption of these small peptides with that of an amino acid mixture with the same small peptide amino acid composition by determining the concentration of individual amino acids in portal blood after a single administration of a nitrogen source. The absorptive intensity of each amino acid was calculated from its rate of elevation in the portal blood; it was higher in the small peptides. The proportion of the amount of each amino acid absorbed in portal blood from small peptides was much more like the composition of the administered amino acids than like that from the amino acid mixture. Among the amino acids administered in the mixture, some amino acids such as L-tyrosine, L-threonine, L-serine and L-histidine increased more slowly in the blood than others. These results suggested that the small peptide formula was utilized more effectively than the amino acid mixture and had higher nutritive value.