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Studies on the tryptophan load test in man.

C Costa, A De Antoni, G Allegri

    La Ricerca in Clinica E in Laboratorio
    |April 1, 1979
    PubMed
    Summary

    The optimal L-tryptophan load test dose is 50 mg/kg body weight for both men and women. Higher doses may cause overloading, especially in women, while lower doses yield insufficient metabolite excretion.

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    Area of Science:

    • Biochemistry
    • Human Physiology
    • Metabolomics

    Background:

    • The tryptophan load test is a method to assess tryptophan metabolism.
    • The kynurenine pathway is a major metabolic route for tryptophan.
    • Understanding sex-based differences in tryptophan metabolism is crucial.

    Purpose of the Study:

    • To determine the optimal L-tryptophan loading dose for assessing urinary tryptophan metabolite excretion.
    • To investigate sex-based differences in tryptophan metabolite excretion patterns.
    • To evaluate the impact of different L-tryptophan doses on metabolite profiles.

    Main Methods:

    • Oral L-tryptophan loading in healthy men and women at doses of 2 g, 50 mg/kg, or 75 mg/kg body weight.
    • Measurement of 10 tryptophan metabolites in urine via the kynurenine pathway.
    • Determination of serum tryptophan levels to establish a 10-hour urine collection period.

    Main Results:

    • Significant differences in metabolite excretion patterns were observed between males and females with increasing L-tryptophan doses.
    • Kynurenine and kynurenic acid were the most abundant metabolites excreted in both groups.
    • The 50 mg/kg body weight dose showed the most consistent and useful metabolite excretion for both sexes.

    Conclusions:

    • A loading dose of 50 mg/kg body weight is recommended for the tryptophan load test in both men and women.
    • Doses of 2 g resulted in low and variable metabolite excretion, while 75 mg/kg posed a risk of overloading, particularly in women.
    • The menstrual cycle did not significantly affect metabolite levels in the tested individuals.

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