Metabolism and excretion of 2,4-[14C]dinitrotoluene in conventional and axenic Fischer-344 rats

Comparisons of in vitro reduction of 2,4-dinitrotoluene (2,4-DNT) by cecal microflora and liver have indicated that microflora may play a large role in the in vivo metabolism of 2,4-DNT to reduced metabolites. Furthermore, reduction of 2,4-DNT by cecal microflora produces nitroso and, presumably, hydroxylamino intermediates which may account for the toxic actions of 2,4-DNT, including hepatocarcinogenesis. This study examines the metabolism, excretion, and hepatic covalent binding of 2,4-DNT in conventional, DNT-fed, and axenic Fischer-344 rats in order to define more precisely the role of DNT pretreatment and intestinal microflora in the disposition and toxicity of 2,4-DNT. No differences in 2,4-DNT disposition were produced by 30 days of feeding DNT (35 mg/kg/day) in the diet of male or female rats. Axenic males and females excreted less of a dose of 2,4-DNT in the urine than did conventional animals, and half-times for excretion of 4-(N-acetyl)amino-2-nitrobenzoic acid (4NAC2NBA), 2,4-dinitrobenzoic acid, 2-amino-4-nitrobenzoic acid (2A4NBA), and 2,4-dinitrobenzyl alcohol glucuronide were longer in axenic males than in conventional males. In axenic females half-times for excretion of only 4NAC2NBA and 2A4NBA were longer than in conventional females. Amounts of 4NAC2NBA and 2A4NBA excreted by axenic animals were 1/10th to 1/5th those excreted by conventional animals. Hepatic covalent binding was decreased by half in axenic animals. These data suggest that intestinal microflora play a major role in the appearance of reduced urinary metabolites and of covalently bound material after 2,4-DNT administration.