Comparative metabolism of 7-methyl- and 7-ethylbenz[a]anthracene by rat-liver preparations

The metabolism of 7-ethyl (7-EBA) and 7-methylbenz[a]anthracene (7-MBA) to dihydrodiols has been compared in incubations with hepatic microsomal fractions prepared from untreated rats. Although both hydrocarbons were found to be metabolised to similar extents, the relative proportions of their diols that were detected differed. For 7-MBA, the principal diols identified were the 8,9- and 5,6-derivatives, whereas for 7-EBA the 8,9- and 1,2-diols predominated; the 5,6-diol was only present as a minor product. These results imply that the presence of the sterically bulky ethyl group at position seven in the benz[a]anthracene ring system may, when compared to the analogous methyl derivative, enhance diol formation on the angular 1,2,3,4 benzo-ring, at the expense of metabolism at the K-region.