Stimulation of specific [3H]-ouabain binding to microsomal preparations from rat heart and skeletal muscle by thyroid hormones: effects of 6-hydroxydopamine.

1. 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. 2. Treatment of thyroidectomized rats with triiodothyronine increased specific [3H]-ouabain binding by 44% in skeletal muscle membrane preparation and 428% in cardiac microsomes. 3. Specific [3H]-ouabain binding decreased by 55% in heart and 53% in gastrocnemius muscle preparations following chemical sympathectomy with 6-hydroxydopamine. 4. 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. 5. Administration of triiodothyronine to thyroidectomized and sympathectomized rats increased specific [3H]-ouabain binding by 80% in heart and 83% in skeletal muscle membrane preparations. 6. 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+ +K+)-adenosine triphosphatase of skeletal muscle membrane is the molecular mechanism for the calorigenic actions of thyroid hormones.