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Effect of leucine on intestinal absorption of tryptophan in rats

Published online by Cambridge University Press:  24 July 2007

Chisae Umezawa
Affiliation:
School of Pharmacy, Kobe-Gakuin University, Nishi-ku, Kobe 673, Japan
Yuko Maeda
Affiliation:
School of Pharmacy, Kobe-Gakuin University, Nishi-ku, Kobe 673, Japan
Kanji Haba
Affiliation:
School of Pharmacy, Kobe-Gakuin University, Nishi-ku, Kobe 673, Japan
Mariko Shin
Affiliation:
School of Pharmacy, Kobe-Gakuin University, Nishi-ku, Kobe 673, Japan
Keiji Sano
Affiliation:
School of Pharmacy, Kobe-Gakuin University, Nishi-ku, Kobe 673, Japan
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Abstract

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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.

Type
Papers on General Nutrition
Copyright
Copyright © The Nutrition Society 1985

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