EFFECT OF THYROID FUNCTION ON NUMBER OF Na-K PUMPS IN HUMAN SKELETAL MUSCLE

To evaluate the effect of thyroid function on the number of Na-K pumps in skeletal muscle, the number of ³H-ouabain binding sites was measured in biopsy specimens from the vastus lateralis muscle of euthyroid subjects and patients with hypothyroidism or hyperthyroidism. In hypothyroidism there was a decrease of 50% in ³H-ouabain binding sites, and in hyperthyroidism there was an increase of 68% in ³H-ouabain binding sites. When thyroid status became normal after treatment the number of ³H-ouabain binding sites also became normal. There were significant correlations between several thyroid function tests and the number of ³H-ouabain binding sites. Free T₄-index gave the highest r value (0·87). These changes may account for the variations in digitalis sensitivity associated with thyroid disorders.