In vivo effect of amiodarone, thiocyanate, perchlorate and goitrin on thyroxine deiodination in rat liver.

The bile duct of male Wistar rats weighing 350 g was cannulated with polyethylene tubing under pentobarbiturate anesthesia and biliary excretion of thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and 3,3'-,3,5- and 3',5'-diiodothyronine (3,3'-T2, 3,5-T2 and 3',5'-T2, respectively) was estimated in 2 h samples of bile with the aid of specific radioimmunoassay. In each animal the excretion of appropriate compounds for 2 h after intravenous injection of various drugs was expressed as per cent of that during 2 h control period before the injection. The results obtained in individual groups of animals were compared to control group which was injected saline before the second bile collection period. The injection of amiodarone (15 mg kg-1) resulted in significant decrease of T3, rT3, 3,3'-T2 and 3,5-T2 excretion and that of thiocyanate (SCN-; 50 mg kg-1) resulted in significantly increased excretion of T4, while that of T3 and 3,5-T2 was significantly decreased. Goitrin (L-5-vinyl-2-oxazolidinethione; 6 mg kg-1) and perchlorate (ClO4-; 50 mg kg-1) showed only slight effects. It was concluded that amiodarone and thiocyanate in the doses used inhibited the conversion of T4 to T3 in vivo immediately after the administration.