Propranolol inhibits the in vitro conversion of thyroxine into triiodothyronine by isolated rat liver parenchymal cells

A model for the in vitro study of the conversion of thyroxine into triiodothyronine using isolated rat liver parenchymal cells is described. Isolated liver cells (mean protein content 18 mg/ml) convert approximately 0.8% of 1.3 microM exogenously added T4 into T3 during thirty minutes incubation. Carbimazole (50 microM) has no effect on the conversion process, whereas propylthiouracil (50 microM) inhibits the conversion. The beta-adrenoceptor blocking agent propranolol lowers the conversion ratio when added in concentrations of 580 and 1160 microM, but has no inhibitory effect when 290 microM is added