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Conjugation and urinary excretion of toluene and m-xylene metabolites in a man
Scandinavian Journal of Work, Environment & Health
Vol. 5, No. 2 (June 1979), pp. 135-142
Published by: the Scandinavian Journal of Work, Environment & Health, the Finnish Institute of Occupational Health, the Danish National Research Centre for the Working Environment, and the Norwegian National Institute of Occupational Health
Stable URL: http://www.jstor.org/stable/40964767
Page Count: 8
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Ingestion of benzoic acid (intermediary metabolite of toluene) by one volunteer subject indicated that the maximum urinary excretion rate of hippuric acid (final metabolite of toluene) was about 190 μmol/min. An almost identical figure for the saturation kinetics of hippuric acid formation has been reported in the literature, and it has been shown to be limited by the availability of glycine for benzoic acid conjugation. The maximum excretory capacity of the kidneys for hippurate is known to be considerably larger than the observed maximum rate of benzoic acid conjugation. In addition the intravenous administration of methylhippuric acid showed that its urinary excretion is rapid, approaching an excretion rate constant of 1.3 h⁻¹. The glycine conjugation of benzoic acid and methylbenzoic acid may well be the ratelimiting step in toluene and, respectively, xylene metabolism. During the inhalation of these solvents, uptake rate may be estimated to equal the full conjugating capacity at a toluene or xylene air concentration of about 780 ppm at rest or of about 270 ppm during moderately heavy work. These data suggest that the body has a relatively large capacity for the conjugation reactions of toluene and xylene metabolism, but the consumption of a large part of easily mobilized glycine may impair the conjugation, and hence excretion, of poorer substrates, e.g., drugs.
Scandinavian Journal of Work, Environment & Health © 1979 Scandinavian Journal of Work, Environment & Health