A single neonatal treatment with methylcholanthrene or benzo(a)pyrene alters microsomal enzyme activity for life.

A single neonatal exposure to methylcholanthrene or benzo(a)-pyrene altered the hepatic microsomal enzyme activity of rats for a long time. Methylcholanthrene depressed, whereas benzo(a)pyrene enhanced the activity of the microsomal enzyme system. The former had a greater influence on males than on females, whereas the latter acted practically uniformly on both sexes.