Maiti_1997_Toxicol.Lett_91_1

The effects of daily administration of dimethoate (2, 4 and 8 mg/kg body weight for 30 days) on thyroid function in mice were investigated. While serum triiodothyronine (T3) concentration was decreased significantly, serum thyroxine (T4) was increased in the medium and highest dose treated groups. However, the serum concentration of thyrotropin was unaltered. Hepatic type-I iodothyronine 5'-monodeiodinase (5'-D) enzyme activity was depressed by the two higher doses of dimethoate. These observations suggest that dimethoate-induced alterations in thyroid function are not mediated through the hypophyseal thyroid axis, but through the changes in extrathyroidal conversion of T4 to T3. To correlate the lipid peroxidation (LPO) with 5'-D activity, hepatic LPO and the activity of antioxidant enzymes, i.e. superoxide dismutase (SOD) and catalase (CAT), were studied. The pesticide increased the activity of SOD and CAT along with hepatic lipid peroxidation. The possible involvement of the lipoperoxidative process in the inhibition of 5'-D activity has been suggested.