The persistence of unmetabolized 3H-7,12-dimethylbenz(a)anthracene in regenerating rat liver.

The hepatic subcellular distribution, binding and persistence of 3H-7,12-dimethylbenz(a)anthracene were compared in partially hepatectomized rats and in intact controls. By 2 weeks after injection, intact liver homogenates contained only 9% of the total radioactivity present 4 h after injection; regenerated liver contained 60% in spite of a tripling in liver mass during this time. Cell fractions isolated from regenerated liver had 9-59 fold greater hexane extractable specific activities than those from intact liver. The radioactivity present in hexane extracts co-chromatographed with a 3H-7,12-dimethylbenz(a)anthracene standard. Preliminary experiments demonstrated that liver microsomes isolated from DMBA treated partially hepatectomized animals metabolized less DMBA in vitro than did microsomes isolated from DMBA treated intact animals. The greater persistence of unmetabolized DMBA may be related to the greater carcinogenicity of this compound for regenerating, as compared with intact, rat liver.