Irreversible fixation of increased level of muscle type aldolase activity appearing in rat liver in the early stage of hepatocarcinogenesis.

azobenzene for 60 days. The muscle type aldolase in the livers of rats thus treated was found to be elevated when compared to nor mal liver, although no appreciable differences were ob served in total aldolase activity, mitotic index, histological architecture, and soluble protein, as well as DNA content. The appearance of this enzymic change was already observable by administrating the azo dye only for 15 days. The increased level of muscle type aldolase activity ob served in the liver of rats fed azo dye for 60 days was maintained during a 300-day observation period. A similar enzymic alteration could be induced by an other hepatocarcinogen, /V,7V'-2,7-fluorenylenebisacetamide, whereas a noncarcinogen, 2-methyl-4-dimethylaminoazobenzene, failed to induce this change.