Inhibition of T3 production in levothyroxine-treated female mice by the root extract of Convolvulus pluricaulis.

An investigation was made to evaluate the role of Convolvulus pluricaulis root extract in the regulation of hyperthyroidism in female mice. Its possible site of action was also studied. L-Thyroxine treatment for 30 days increased serum concentrations of thyroxine (T4) and triodothyronine (T3). The activity of hepatic 5'-monodeiodinase (5'-DI) and glucose-6-phosphatase (G-6-Pase) was also enhanced. On the other hand, administration of the plant extract either alone or with L-T4, decreased serum T3 concentration and the activity of hepatic 5'-DI and G-6-phase, without marked alteration in hepatic lipid peroxidation, indicating the possible regulation of hyperthyroidism by the plant extract. It appears that the action of the plant extract on thyroid function is primarily mediated through the inhibition of 5'-DI enzyme activity.