Effect of the glycogenolytic gluconeogenetic hormones, glucagon, vasopressin and angiotensin II, on biliary excretion of iodothyronines in rats is possibly related to the inhibition of 5′-monodeiodination in the liver

Abstract

ABSTRACT Polyethylene tubes were inserted into the bile duct and femoral vein of rats under pentobarbital anaesthesia and bile was collected for three 2-h periods. After the first (control) period the animals were infused intravenously at a rate of 1·2 ml/h with the following compounds: (1) 0·9% (w/v) NaCl (control group), (2) glucagon (1200 ng/h), (3) vasopressin (1200 ng/h) or (4) angiotensin II (600 ng/h). The concentrations of thyroxine (T4), tri-iodothyronine (T3) and reverse tri-iodothyronine (rT3) in the bile were estimated by radioimmunoassay. No significant differences between groups were found in the biliary excretion of T4 and T3, while the excretion of rT3 after the infusion of all the hormones used was significantly (P < 0·001 at 2 to 4 h of the infusion) increased, no such increase being found in the controls. It may be concluded therefore that the administration of the above hormones resulted in some changes in iodothyronine metabolism in the liver. These may be explained by an inhibition of iodothyronine 5′-monodeiodination related to the glycogenolytic and gluconeogenetic effects of these hormones. Journal of Endocrinology (1989) 121, 299–302