Effect of leucine on intestinal absorption of tryptophan in rats.
1. To elucidate the causal relation between leucine and the lowering of hepatic NAD content of rats fed on a leucine-excessive diet (Yamada et al. 1979), the effect of leucine on intestinal absorption of tryptophan was investigated. 2. Co-administration of [3H]tryptophan and leucine, with leucine at ten times the level of tryptophan, delayed absorption of L-[side chain 2,3-3H]tryptophan from the digestive tract and incorporation of [3H]tryptophan into portal blood, the liver and a protein fraction of the liver. After 120 min, more than 95% of tryptophan was absorbed whether [3H]tryptophan was administered with or without leucine. 3. Co-administration of a mixture of ten essential amino acids, in proportions simulating casein, with [3H]tryptophan markedly delayed absorption of tryptophan from the digestive tract. The addition of supplementary leucine to the amino acid mixture, however, caused no further delay. 4. In rats prefed a leucine-excessive diet for 1 week [3H]tryptophan was absorbed at the same rate as in rats fed on a control diet. 5. The results indicate that competition between tryptophan and leucine for intestinal absorption did not cause lowering of hepatic NAD.
D000601:Amino Acids, Essential / Q000494:pharmacology; D000818:Animals; D002364:Caseins / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects*; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism; D008297:Male; D009243:NAD / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014364:Tryptophan / Q000097:blood / Q000493:pharmacokinetics*
D000601:Amino Acids, Essential; D002364:Caseins; D009243:NAD; D014364:Tryptophan; D007930:Leucine