Liver growth associated with the induction of demethylase activity after injection of 3-methylcholanthrene in immature rats.

SUMMARY One intraperitoneal injection of 1 mg of 3-methylchol anthrene into immature male and female rats results in an increase in azo dye demethylase activity. This is followed by an increase in wet and dry liver weight and in total protein, which reaches a peak of about 30†" 40% above control levels within 3 or 4 days. Cell proliferation contributes to the in crease in liver weight and protein as indicated by an increase in the total DNA and nuclear count. Some of the increase in cell number is probably due to hepatocyte proliferation since there is an increase in heptaocyte mitotic activity. Between 5 and 7 days after injection of 3-methylcholan threne, the liver weight, protein, DNA, and nuclear count be gin to decrease to control values, which they reach by 14 days. The decline in these parameters of liver growth is closely asso ciated with a decrease in the azo dye demethylase activity.