Action of the thyroid hormone at the level of the plasma membrane

In this presentation, I present evidence indicating a direct action of thyroid hormone at the level of the plasma membrane. Characteristically, the plasma membrane-mediated effects of thyroid hormones are prompt in onset, independent of new protein synthesis, and are associated with changes in the transmembrane transport of ions and substrates. The presence of specific binding sites for thyroid hormone in plasma membrane of various tissues and species, although inconclusive in itself, provides additional support for the direct action of thyroid hormone on the plasma membrane. A model for the mechanism of action of thyroid hormone at the plasma membrane level to increase sugar uptake by rat thymocytes is delineated, and the physiological role of the plasma membrane-mediated action of thyroid hormone is discussed.