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Effect of Force-feeding Diets Lacking Leucine, Valine, Isoleucine, Threonine or Methionine on Amino Acid Catabolism in Rats

Laboratory of Food and Nutrition, Faculty of Science of Living, Osaka City University, Sumiyoshi, Osaka, Japan

To investigate the effect of a deficiency of one amino acid on amino acid catabolism, rats were force-fed a 10% amino acid diet devoid of one or two essential amino acids. Body weight changes, urinary nitrogen, liver tryptophan pyrrolase (L-tryptophan:oxygen oxidoreductase, EC 1.13.1.12, TPase) and tyrosine--ketoglutarate transaminase (L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5, TKase) activities, and trichloroacetic acid-soluble nitrogen of the gastrointestinal contents were measured. a) There were lower activity of TKase and delayed disappearance of dietary nitrogen from the gastrointestinal tract of rats force-fed the leucine-free diet or the diets lacking in leucine and another amino acid than in rats fed diets lacking other amino acids. b) Force-feeding valine-free diets resulted in a time lag of TPase activity-induction and delayed disappearance of dietary nitrogen from the gastrointestinal tract. These effects were not eliminated by the further omission of leucine or isoleucine from the valine-free diet. c) Acute weakness of rats fed the valine-free diet could be retarded by the omission of leucine from this diet. These results indicated that these specific effects of leucine and valine deficiencies depend upon the difficulty in catabolism of amino acids, and that the presence of leucine or valine in a diet might play a specific role in adrenalcortical hormone secretion.

KEY WORDS: • leucine • valine • isoleucine • threonine • methionine • catabolism

Manuscript received 9 June 1971.