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  • Title: Effects of two different loading doses of L-tryptophan on the urinary excretion of tryptophan metabolites in rats, mice and guinea pigs. Correlation with the enzyme activities.
    Author: Allegri G, Costa C, Baccichetti F, Biasiolo M.
    Journal: Ital J Biochem; 1987; 36(3):194-203. PubMed ID: 3610599.
    Abstract:
    The effect of two different loading doses of L-tryptophan (0.5 and 1.0 g/Kg b.w.) on excretion of tryptophan metabolites and the relation to the enzyme activities were studied in rats, mice and guinea pigs. In rats there is no ratio between the dosage used and the levels of the metabolites excreted. Doubling the amount of tryptophan administered, a 5-fold increase in the elimination of the metabolites along the kynurenine pathway is obtained. The 1.0 g/Kg load provides a more complete pattern of the metabolites than with the 0.5 g/Kg b.w. load. Kynurenic acid, kynurenine and xanthurenic acid are the chief metabolites excreted. In mice, the urinary excretion of the metabolites is very low with both loads. In guinea pigs, xanthurenic acid is excreted in the highest amount and kynurenic acid and kynurenine also constitute the large fractions with both loadings. The load of 0.5 g/Kg b.w. is preferable to that of 1.0 g/Kg b.w. for not causing B6-deficiency. Liver tryptophan pyrrolase exists in two forms in rats, while in mice and in guinea pigs it is present only as holoenzyme. This enzyme is more active in rats than in the other two species of animals. Kynureninase activity is lower in guinea pigs, but it apparently correlated to the low levels of excretion of the metabolites following this step. Kynurenine aminotransferase is very active in rats and in mice, while it is apparently depressed in guinea pigs, in contrast with the high excretion of xanthurenic and kynurenic acids, that puts in evidence a B6-deficiency. The excretion of tryptophan metabolites and enzyme activities are better correlated in rats.
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