Chronic hepatotoxicity and intestinal bleeding in 1,2-dimethylhydrazine carcinogenesis in rats and mice.

The long term administration of dimethylhydrazine to mice induces severe hepatotoxic damage. Parenchymal cell pleomorphism and necrosis were later associated with reticulin collapse and bile duct proliferation. Withdrawing the drug after 17 weeks was followed by some improvement in the parenchymal cells but there was a chronic proliferative response tending towards early cirrhotic changes. The rats appeared relatively resistant to the hepatotoxic effects but unlike the mice the colon tumors arising in these animals bled frequently and could result in profound anemia.