Effect of Different β-Blocking Drugs and Adrenaline on the Conversion of Thyroxine to Triiodothyronine in Isolated Rat Hepatocytes

Summary

The in vitro effect of various selective and non-selective β-blocking drugs and adrenaline on the conversion of thyroxine (T₄) to triiodothyronine (T₃) was studied in suspensions of isolated rat hepatocytes after 90 min of incubation.

Compared with the untreated controls propranolol caused a dose-related inhibition of the T₄ to T₃ conversion in conc of 100, 200 and 400 μM. The other β-blocking drugs studied, timolol, oxprenolol, atenolol and metoprolol, were without any effect on this in vitro conversion. Propranolol did not interfere with the cellular association of T₄ or the degradation of T₄ and T₃. Adrenaline 200 μM caused a small decrease of T₃ in the medium and a corresponding increase in the intracellular content of T₃. The inhibitory effect of propranolol 200 μM was not antagonized by equimolar concentrations of adrenaline.

Our study suggests that the inhibitory effect of propranolol on the conversion of T₄ to T₃ in hepatocytes is caused by a direct chemical effect of the drug unrelated to its β-blocking and membrane stabilizing properties.

Rat Hepatocytes - Thyroxine - Triiodothyronine - β-Blocking Drugs - Propranolol - Timolol - Oxprenolol - Atenolol - Metoprolol - Adrenaline