Effect of ethanol and linoleic acid on changes in biliary excretion of iodothyronines possibly related to thyroxine deiodination in rat liver

Groups of male rats weighing about 350 g were inserted polyethylene tubings into bile duct and femoral vein under pentobarbital anesthesia. Several iodothyronines (i.e. T4, T3, rT3, 3,5-T2, 3,3'-T2 and 3',5'-T2) were estimated in 2-hr portions of bile with the aid of specific radioimmunoassay. After the infusion of ethanol (0.3 ml/hr/rat for 4 hr) an increase of biliary excretion of rT3 and a decrease of 3,5-T2 was found as compared to controls. When 5 mg linoleic acid was added to 1.2 ml ethanol, the increase of rT3 was significantly higher than that after ethanol only and, in addition, significant increase of 3',5'-T2 excretion was found. It was concluded that both ethanol and unsaturated fatty acids may inhibit 5'-monodeiodination in the liver and that unsaturated nonesterified fatty acids may exert such effect even when administered intravenously without underlying metabolic disorders.