Polychlorinated biphenyls and naphthalenes: Long-lasting induction of oxidative stress in the rat

A single dose of polychlorinated biphenyls (PCBs; 100 mg/kg) or naphthalenes (PCNs; 20 mg/kg) was given i.p. to male Sprague-Dawley rats. After 1, 3, 7 or 14 days or 3 months hepatic cytochrome P450 activities, lipid peroxidation status, vitamin A or E and glutathione (GSH) content, and antioxidative enzyme activities were evaluated. PCBs and PCNs induced EROD (7-ethoxycoumarin O-deethylase) activity up to 50-fold and the activity was still elevated after 3 months. Concomitantly to this P450 induction the lipid peroxidation level (conjugated dienes) increased 2-fold. PCBs decreased hepatic vitamin A and E content and both chemicals decreased catalase and superoxide dismutase activities. Glucose-6-phosphate dehydrogenase and GSH-S-transferase activities and GSH-content were increased; GSH-peroxidase activity was not affected. In conclusion, these halogenated aromatic hydrocarbons caused a long-lasting impairment in the antioxidative defence system and an increase in oxidative stress in rat liver. These effects are probably closely linked with the ability of these chemicals to act as tumor promoters.