The extrathyroidal conversion of T4 to T3 in the striped racer snake, Elaphe taeniura

Abstract

The extrathyroidal conversion of thyroxine to triiodothyronine in the snake, Elaphe taeniura, has been determined in vitro. The liver, kidney and pancreas are important organs showing significant 5′-deiodinase activity. The pancreas has a higher conversion rate (18.5±3.58 pmol·min-1·mg protein-1) than other vertebrate tissues that have been studied. The 5′-deiodinase activity is dependent on substrate (thyroxine) concentration, cofactor, i.e. dithioerythritol concentration, temperature, duration of incubation and pH. It is sensitive to iopanoic acid, propylthiouracil, salicylate and propranolol. It is also indicative that the 5′-deiodinase activity increased and decreased, respectively, in snakes with experimentally induced hyper- and hypo-thyroidism. These characteristics suggest that snake 5′-deiodinase is similar to that of mammals, probably of type I category.