Antithyroid effects of naringin, hesperidin and rutin in l-T4 induced hyperthyroid rats: possible mediation through 5'DI activity.

Background: Investigations are meager on the ameliorative role of plant based active compounds in regulating hyperthyroidism. We have now explored the possible role of three flavonoids in the regulation of L-thyroxine (l-T4)-induced hyperthyroidism in rats. This investigation attempts to reveal whether rutin, naringin and hesperidin supplementation exhibit antithyroid effects in L-T4-induced hyperthyroid rats and to work out the possible involvement of free radicals in their mode of action.

Methods: Either rutin or naringin or hesperidin (50mg/kg each) was administered to L-T4-induced hyperthyroid rats for two weeks and their effects were evaluated on the alterations in levels of thyroid hormones, 5'-deiodinase I (5'DI) activity, hepatic lipid peroxidation as well as in antioxidants.

Results: l-T4 administration significantly enhanced the serum concentrations of thyroxine and triiodothyronine; the activities of hepatic 5'DI, serum lactate dehydrogenase and serum glutamate pyruvate transaminase along with an increase in content of malondialdehyde in hepatic tissues, but depleted the cellular antioxidants. However, on administration of the test flavonoids, these effects were more or less normalized. Electro paramagnetic resonance (EPR) spectra also indicated the suppression of the hydroxyl radicals (OH) in the hepatic tissues.

Conclusion: Rutin, naringin and hesperidin have the potential to inhibit thyroid functions without hepatotoxicity and the effects are possibly mediated through their free radical scavenging action as evidenced by EPR study. From the comparative analyses of the results, rutin appeared to be the most effective one suggesting its better antithyroid and antioxidative potential over other two.