Summary.-The basal concentration of the tryptophan metabolite 3-hydroxyanthranilic acid (30HA), which has carcinogenic properties, was measured with an enzymatic method of determination which allowed separate measurement of free and conjugated 30HA. The concentration of free 30HA in untreated bladder cancer patients was significantly (P < 0.001) higher than in a healthy control group, but after local therapy the concentration was significantly lower than before treatment (P < 0-01). The concentration of conjugated 30HA was nearly constant in the three groups. It was concluded that other factors than a genetic determined abnormality might be operating in bladder cancer patients which could lead to an abnormal concentration of 30HA in their urine.'rHE role of tryptophan metabolites in the aetiology of human urinary bladder cancer has been the subject of numerous investigations. Twenty-two years ago a relationship was suggested by Dunning, Curtis and Maun (1950), who showed that a high incidence of bladder tumours resulted when rats were fed 2-acetylaminofluorene combined with DL-tryptophan. Several primary aromatic amine tryptophan metabolites, with a structure similar to known environmental human bladder carcinogens, are present in human urine (Brown and Price, 1956). Direct application to the mouse bladder of these metabolites by the " pellet technique " confirmed the carcinogenic activity of several of them (Bryan, 1971). Recently, Radomski, Glass and Deichmann (1971) have given evidence supporting the role of tryptophan in bladder carcinogenesis by feeding 7 times the normal daily intake of DL-tryptophan to beagle dogs for periods of 3 5 months to 7 years. Marked local hyperplasia of the transitional bladder epithelium was observed in all cases.Several clinical studies of the metabolism of tryptophan have been carried out in patients with bladder cancer (Brown et al., 1960;Price and Brown, 1962;Benassi, Perissinotto and Allegri, 1963;Kochen and Hochberg, 1970). In these investigations one or more metabolites were determined in samples of 24-hour urine. In most of the studies, loading with an oral dose of L-tryptophan was necessary because the analytical methods are working at lower limits of detection and sensitivity when used on basal urines. Because of the differences in method, it is difficult to compare the results obtained in the different laboratories. An abnormal metabolism was often observed in patients with spontaneous bladder cancer, but in other pathological conditions an abnormal excretion pattern was also found (Rose,.Moreover, the excretion of metabolites is related to tryptophan intake, hormonal regulation of the pathway, intake levels of pyridoxine and metabolic individualitv (Albanese et al., 1972). In a pilot study
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