Studies in detoxication. 85. The metabolism of m-dinitro[14C]benzene in the rabbit

Abstract

The metabolism of m-dinitro[C14]benzene was studied in the rabbit at oral doses of 50-100 mg/kg; 65-93% of the dose was excreted in the urine during the first 2 days and 1-5% in the feces. The principal metabolites in the urine were 2,4-diaminophenol (31% of dose), m-phenylenediamine (21%), m-nitroaniline (14%), and 2-amino-4-nitrophenol (14%). Traces of unchanged m-dinitrobenzene (0.7%), 2,4-dinitrophenol (0.1%). 4-amino-2-nitrophenol (0.8%), m-nitrophenylhydroxylamine (0.8%), m-nitrosonitrobenzene (0.25%) and 3,3''-dinitroazoxybenzene (0.3%) were also present. 2,6- and 3,5-Dinitrophenol, 2-amino 6-nitrophenol and 3-amino-5-nitrophenol, and 2,6 and 3,5-diaminophenol, were not present in amounts greater than 0.05% of the dose. With oral doses of non-radioactive m-dinitrobenzene, an average of 30% of the dose was excreted as glucuronide conjugates and 6% as ethereal sulphates. 2,4-Diaminophenol, m-phenylenediamine, m-nitroaniline, 2-amino-4-nitrophenol, 2,4-dinitrophenol, 3,3''-dinitroazoxybenzene, m-nitroso-nitrobenzene, and unchanged m-dinitrobenzene, or derivatives of these were isolated from the urine of rabbits dosed with m-dinitrobenzene. The presence of 4-amino-2-nitrophenol was confirmed by paper chromatography and UV-absorption spectra. The UV-absorption spectra of 2,4- and 2,6- and 3,5-dinitrophenol in 0.1 N-hydrochloric acid and 0.1 N-NaOH are recorded, and the absence of these dinitrophenols except for traces of 2,4-dinitrophenol (0.1% of dose) was confirmed from UV spectra of extracts of the hydrolysed urine from rabbits dosed with m-dinitrobenzene. 4-Amino-2-nitrophenol was estimated after acid hydrolysis (2.0% of dose), and after enzymic hydrolysis (0.8% of dose). The estimation after acid hydrolysis includes 4-amino-2-nitrophenol arising as an artifact of 3-nitrophenylhydroxylamine (0.8% of dose). In 2 experiments with m-dinitro[C14]benzene, no m-phenylenediamine was formed and the amounts of m-nitroaniline present in the urine were approximately equal to the sum of the 2 reduction products (35% of dose) formed in other experiments. The reduction of m-dinitrobenzene to m-phenylenediamine was inhibited by Aureomycin (chlortetracycline). A mechanism for the reduction of aromatic nitro compounds involving flavin free radicals was postulated.