STIMULATION OF SPECIFIC [OUABAIN-H-3 BINDING TO MICROSOMAL PREPARATIONS FROM RAT-HEART AND SKELETAL-MUSCLE BY THYROID-HORMONES - EFFECTS OF 6-HYDROXYDOPAMINE

Surgical thyroidectomy decreased specific [3H]‐ouabain binding to heart ventricular microsomes by 43% and gastrocnemius muscle microsomes by 34%. Administration of triiodothyronine to euthyroid rats enhanced specific [3H]‐ouabain binding to heart and skeletal muscle membrane by 60% and 33% respectively. Treatment of thyroidectomized rats with triiodothyronine increased specific [3H]‐ouabain binding by 44% in skeletal muscle membrane preparation and 428% in cardiac microsomes. Specific [3H]‐ouabain binding decreased by 55% in heart and 53% in gastrocnemius muscle preparations following chemical sympathectomy with 6‐hydroxydopamine. Treatment with triiodothyronine of euthyroid rats which had been sympathectomized did not significantly alter specific [3H]‐ouabain binding to heart or skeletal muscle membrane preparations. Administration of triiodothyronine to thyroidectomized and sympathectomized rats increased specific [3H]‐ouabain binding by 80% in heart and 83% in skeletal muscle membrane preparations. These results suggest that triiodothyronine may influence specific [3H]‐ouabain binding to thyroid hormone nonresponsive tissue such as sympathetic nerve endings. Therefore, the present observations are incompatible with the hypothesis that induction of (Na+ 4‐ K+)‐adenosine triphosphatase of skeletal muscle membrane is the molecular mechanism for the calorigenic actions of thyroid hormones. 1979 British Pharmacological Society