N-glucuronide formation of carcinogenic aromatic amines in rat and human liver microsomes

(1) Sensitive fluorimetric assays were developed for the determination of microsomal UDP-glucuronosyltransferase activities towards 1- and 2-naphthylamine and 4-aminobiphenyl. (2) In rat liver microsomes, enzyme activity towards 1-naphthylamine was orders of magnitude higher than the activities towards 2-naphthylamine, 4-aminobiphenyl or aniline. The differences were less marked with human liver microsomes. (3) Glucuronidation of aniline and 4-aminobiphenyl was not appreciably altered in rat liver microsomes from 3-methylcholanthrene- or phenobarbital-treated rats. UDP-glucuronosyltransferase activities towards 1- and 2-naphthylamine were selectively increased (about 2-fold) by 3-methylcholanthrene-treatment. However the increases were less marked than those observed with representative substrates of the 3-methylcholanthrene-inducible enzyme form. The results suggest that the arylamines investigated are predominantly conjugated by constitutive enzyme forms in rat liver. (4) Arylamine N-glucuronides were found to be susceptible to hydrolysis by E. coli beta-glucuronidase suggesting the release of carcinogenic arylamines in the gut and their enterohepatic circulation.