Metabolism of di-, tri- and tetrabromobiphenyls by hepatic microsomes isolated from control animals and animals treated with Aroclor 1254, a commercial mixture of polychlorinated biphenyls (PCBs).

1. The metabolism of di-, tri- and tetrabromobiphenyls (PBBs) by hepatic microsomes isolated from control animals and animals treated with Arochlor 1254 was studied. 2. Hepatic microsomes isolated from control rats expressed higher rates of oxidations than avians. 3. Treatment of rats and pigeons with Arochlor 1254 induced cytochrome P450 dependent monooxygenases leading to an increased regioselective metabolism of PBB isomer and congeneres. 4. There was an inverse relationship between the degree of halosubstitution and microsomal oxidation. Meta-para carbon atoms free of halosubstitution were the preferred side for oxidation.