Stress Is Associated with Inhibition of Type I Iodothyronine 5′‐Deiodinase Activity in Rat Liver

A bstract : Type I iodothyronine deiodinase (5′‐DI) generates the thyromimetically active hormone 3,5,3′‐triiodothyronine (T 3 ) by reductive monodeiodination of the phenolic ring of L‐thyroxine (T 4 ). The present study was undertaken to compare the effects of cold stress (4°C) alone or in combination with immobilization stress (IMO), insulin treatment (5 IU/kg, i.p.) or 2‐deoxy‐D‐glucose (2DG)‐induced intracellular glucopenia on the activity of 5′‐DI in rat liver. Cold stress either for 24 h or 28 days when compared to that in the nonstressed group of rats significantly reduced ( P < 0.001 ) the activity of 5′‐DI in liver. In comparison with cold stressed rats for 28 days, an additional decrease in 5′‐DI activity was observed when those rats underwent 1 × IMO in cold for 2 h ( P < 0.001 ) or insulin treatment ( P < 0.05 ). A significant decrease in 5′‐DI activity was found also in rats maintained at room temperature that underwent a single 1 × IMO for 2 h ( P < 0.001 ) or insulin treatment ( P < 0.01 ) when compared to nonstressed animals. In comparison with nonstressed rats, no significant change of the 5′‐DI activity was observed after 2DG application (500 mg/kg, i.p.) at room temperature. In conclusion, cold stress and/or 1 × IMO, insulin treatment, or 1 × IMO at room temperature markedly affects reductive monodeiodination of T 4 , and thus reduces the concentration of biologically active T 3 in liver.