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Research Article Free access | 10.1172/JCI105785

Circadian periodicity of tryptophan metabolism

Morton I. Rapoport and William R. Beisel

Division of Infectious Diseases, University of Maryland School of Medicine, Baltimore

U. S. Army Medical Unit, Walter Reed Army Medical Center, Frederick, Maryland 21701

Find articles by Rapoport, M. in: PubMed | Google Scholar

Division of Infectious Diseases, University of Maryland School of Medicine, Baltimore

U. S. Army Medical Unit, Walter Reed Army Medical Center, Frederick, Maryland 21701

Find articles by Beisel, W. in: PubMed | Google Scholar

Published April 1, 1968 - More info

Published in Volume 47, Issue 4 on April 1, 1968
J Clin Invest. 1968;47(4):934–939. https://doi.org/10.1172/JCI105785.
© 1968 The American Society for Clinical Investigation
Published April 1, 1968 - Version history
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Abstract

Rhythmicity of tryptophan metabolism via the kynurenine pathway has been demonstrated in man. Normal subjects given 3 g of tryptophan at 0900 hours excreted almost three times the quantity of kynurenine, kynurenic acid, and xanthurenic acid than did subjects given the same dose at 2100 hours. Other metabolites of the kynurenine pathway varied in the same fashion but with lesser magnitude. In contrast, indican, a tryptophan metabolite not in the kynurenine pathway, varied inversely with the other metabolites measured. The data suggest that the liver enzyme tryptophan pyrrolase has a circadian rhythm in man similar to that already described in mice in a previous study.

Tryptophan tolerance tests in the future should be controlled relative to time of amino acid administration.

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