Tryptophan metabolism in the cat: a study with carbon-14-labeled compounds
Leklem, J.E.; Brown, R.R.; Hankes, L.V.; Schmaeler, M.
American Journal of Veterinary Research 32(2): 335-344
1971
ISSN/ISBN: 0002-9645 PMID: 4250971 Document Number: 2792
To study inefficient conversion of tryptophan to nicotinic acid observed in vivo and to find cause for low urinary concentrations of tryptophan metabolites and low incidence of urinary bladder cancer reported in cats, metabolism of tryptophan was determined by intraperitoneally injecting c ats with L- tryptophan-7a- 14C, L-kynurenine-keto- 14C, L-kynurenine-ring-214ri, 3-hydroxy-L-kynurenine-keto- 14C, 3-hydroxyanthranilic acid -carboxyl 14C, and anthranilic acid -carboxyl -14C. The expired 14CO2 indicated that rapid metabolism of L-kynurenine, 3-hydroxy-L-kynurenine, and 3-hydroxya nthranilic acid occurred. Urinary radioactivity accounted for 5.4 to 11.8% of the dose of L-tryptophan, L-kynurenine, and 3-hydroxy-L-kynurenine and 26.0 to 32.8% of the 3-hydroxyanthranilic acid. The cat efficiently c onverted anthranilic acid into o-aminohippuric acid. Except in cats given anthranilic acid and 3-hydroxyanthranilic acid, less than 4% (i.e., 0.76 to 3.59%) of the dose given was accounted for in urine as known tryptophan metabolites, including kynurenine, o-aminohippuric acid, 3-hydroxykynurenme, kynurenic acid, xanthurenic acid, quinolinic acid, picolinic acid, Ni_ rnethylnicotinamide, N 1-methyl-2-pyridone-5-carboxamide, and nicotinic acid. A small, but detectable, conversion of typtophan to nicotinic acid metabolites was observed. The low concentrations of carcinogenic tryptophan metabolites in cat urine may offer an explanation for the relatively low incidence of urinary bladder neoplasms reported in the cat as compared with other species.
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