1. The corresponding cysteine conjugate was formed when the GSH (reduced glutathione) or cysteinylglycine conjugates of benzyl isothiocyanate were incubated with rat liver or kidney homogenates. When the cysteine conjugate of benzyl isothiocyanate was similarly incubated in the presence of acetyl-CoA, the corresponding N-acetylcysteine conjugate (mercapturic acid) was formed. 2. The non-enzymic reaction of GSH with benzyl isothiocyanate was rapid and was catalysed by rat liver cytosol. 3. The mercapturic acid was excreted in the urine of rats dosed with benzyl isothiocyanate or its GSH, cysteinyl-glycine or cysteine conjugate, and was isolated as the dicyclohexylamine salt. 4. An oral dose of the cysteine conjugate of [14C]benzyl isothiocyanate was rapidly absorbed and excreted by rats and dogs. After 3 days, rats had excreted a mean of 92.4 and 5.6% of the dose in the urine and faeces respectively, and dogs had excreted a mean of 86.3 and 13.2% respectively. 5. After an oral dose of the cystein conjugate of [C]benzyl isothiocyanate, the major 14C-labelled metabolite in rat urine was the corresponding mercapturic acid (62% of the dose), whereas in dog urine it was hippuric acid (40% of the dose). 5. Mercapturic acid biosynthesis may be an important route of metabolism of certain isothiocyanates in some mammalian species.

1. After oral administration of aristolochic acid I (AAI) and aristolochic acid II (AAII) to rats, the following metabolites were isolated from the urine and their structures elucidated: aristolactam I, aristolactam Ia, aristolochic acid Ia, aristolic acid I and 3,4-methylenedioxy-8-hydroxy-1-phenanthrenecarboxylic acid (metabolites of AAI); or aristolactam Ia, aristolactam II and 3,4-methylenedioxy-1-phenanthrenecarboxylic acid (metabolites of AAII). A further metabolite of AAII having a lactam structure has not yet been isolated in pure form. 2. The metabolic pathways have been elucidated by administration of various metabolites. 3. The principal metabolite of AAI in rats was aristolactam Ia; 46% of the dose was excreted in the urine in form of this metabolite and 37% in the faeces. The other substances were minor metabolites. Those metabolites of AAII whose structures have been elucidated were minor metabolites; the largest proportion consisted of aristolactam II, which accounted for 4.6% in the urine and 8.9% in the faeces. 4. The mouse was the only animal which had the same metabolite patterns of AAI and AAII as those found in the rat. Not all the metabolites listed above were found in urine from guinea pigs, rabbits, dogs and man.

1. Both after ingestion of benzyl isothiocyanate (BITC), a compound with antibacterial properties, and after consumption of garden cress known to contain BITC, the metabolite N-acetyl-S-(N-benzylthiocarbamoyl)-L-cysteine was identified in the urine of volunteers by comparative chromatography. 2. The chemical structure of the metabolite was confirmed by elemental analysis and by comparison of the i.r. and 1H-n.m.r. spectra with those of the synthetic product. 3. On average 53.7% of the dose of BITC was excreted as this metabolite by the renal route. 4. The metabolite was excreted rapidly, appearing with maximum concentrations some 2-6 h after dosing and being essentially complete 10-12 h after administration.

The metabolism of methyl, ethyl, butyl and allyl isothiocyanate, which occur as glucosinolates in a number of plants, was studied. Oral administration of the substances to the rat was followed by their renal excretion as mercapturic acids, which were isolated as dicyclohexylamine salts. Chemical structure was determined by synthesis and 1H-n.m.r. spectra. The mercapturic acids were very labile dithiocarbamidic acid esters, formed by the addition of the isothiocyanate group to the SH group of the cysteine component.

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