An oxidative mechanism for the inhibition of iodothyronine 5 '-monodeiodinase activity by lead nitrate in the fish, Heteropneustes fossilis

An oxidative mechanism in the lead-induced inhibition of thyroid function w ith special reference to iodothyronine 5'-monodeiodinase (5'-ID) activity h as been identified in the fish, Heteropneustes fossilis. Lead treatment (2. 5, 5.0 and 10.0 ppm of lead nitrate/day for 30 days) enhanced tissue lipid peroxidation (LPO) and decreased the activity of antioxidant enzymes such a s superoxide dismutase (SOD) and catalase (CAT). In addition, serum triiodo thyronine (T-3) concentration and hepatic 5'-ID activity were markedly decr eased by 10 ppm of lead nitrate. These findings support the view that highe r concentrations of lead nitrate inhibit the extrathyroidal conversion of t hyroxine (T-4) to T3 Moreover, oxidative stress from lead intoxication coul d be responsible for inhibiting 5'-ID activity.