Free amino acid concentrations in the gut lumen of developing rats.

Free amino acid concentrations in the lumen and tissue of small intestine of suckling rats were measured by a micromethod. Almost all amino acid concentrations (Lys excepted) in the intestinal juice decrease until 15 days of age whereby the pattern remains constant. Concomitantly, free amino acid concentrations in the intestinal tissue increase between 10 and 15 days p.p. The pool of amino acids in the intestinal juice, reflecting the nutritional input and its utilization, becomes exhausted during the suckling period. At 20 days of age the rats additionally ate the rat chow and free amino acid concentrations in the intestinal tissue increased again. The decline of the amino acid pool in the lumen of small intestine which is both derived by the mother and exhausted by the growing organism may act as a signal for differentiation via (self-) restriction of substrates for protein accretion.