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Lack of Effect of Smoking on the Excretion of Tryptophan Metabolites by Man¹

Division of Clinical Oncology, University of Wisconsin Medical School, Madison, Wisconsin 53706 [R. R. B., J. M. P.], and the Cancer Research Institute, New England Deaconess Hospital, Boston, Massachusetts 02118 [S. W. B., G. H. F.]

Urinary excretion of tryptophan and niacin metabolites was measured before and after oral loads of 2.0 g L-tryptophan in 12 normal smokers, in the same subjects after having stopped smoking for 3 weeks, and again after resumption of smoking. The metabolites measured were kynurenine, hydroxykynurenine, kynurenic acid, xanthurenic acid, acetylkynurenine, o-aminohippuric acid, anthranilic acid glucuronide, N¹-methylnicotinamide, and N-methyl-2-pyridone-5-carboxamide. Also measured were 4-pyridoxic acid and creatinine as respective indices of nutrition and reliability of collections and nicotine as an index of smoking. Nicotine values indicated that the subjects had faithfully stopped smoking during the nonsmoking period. With the exception of an inconsistent change in acetylkynurenine excretion, no significant changes were observed in the excretion of any of the metabolites measured. Additional studies comparing 17 regular male smokers (average smoking history of 15 cigarettes/day for 9.5 years) with 13 male nonsmokers failed to show any differences in urinary excretion of these metabolites. The present data do not refute the statistical association between smoking and bladder cancer, but they do suggest that this association is not mediated by altered urinary excretion levels of tryptophan or niacin metabolites in smokers.

¹ The work in Wisconsin was supported in part by National Cancer Institute Grant CA-03274, USPHS; American Cancer Society Grant T-445G; and grants from the Elsa U. Pardee Foundation and the Council for Tobacco Research-U. S. A. The work in Boston was supported in part by National Cancer Institute Grant CA-10210, USPHS; USPHS General Research Support Grant FR-5591-03; and a grant from the Council for Tobacco Research-U. S. A.

² Supported by National Cancer Institute USPHS Research Career Development Award 5-K3-CA18,404.

³ Present address: Abbott Laboratories, North Chicago, Ill.

Received 7/18/69. Accepted 7/23/69.