Studies on nitrogen and amino-acid absorption in the swine. Part 2. The course of 15 N labeling in the chyme, urine and blood

Three female pigs provided with re-entrant canulas at the beginning and the end of the small intestine and catheterized for blood and urine collection were once fed a 15N-labelled mixed diet. Until 48 hours after feed intake chyme from the canulas and urine and blood were collected at varying intervals. All 15N-frequencies measured in the duodenal chyme were found to be below the labelling of the feed protein. Until 11 hours after intake of the labelled feed, the residue obtained by centrifugation of the intestinal contents revealed the highest 15N-labelling. Only slight differences were found in the frequencies of the other fractions (proteins, peptides, free amino acids). The almost constant labelling of all fractions in that period is indicative of a dilution with endogenous nitrogen being constant in comparison with food N. The 15N-frequencies of the chyme fractions observed at the end of the small intestine allowed to conclude that the breakdown of the food proteins is more complete than the disintegration of the endogenous proteins.