RT Book, Section A1 Brent, Gregory A. A1 Koenig, Ronald J. A2 Brunton, Laurence L. A2 Chabner, Bruce A. A2 Knollmann, Björn C. SR Print(0) ID 1127869305 T1 Thyroid and Anti-Thyroid Drugs T2 Goodman & Gilman's: The Pharmacological Basis of Therapeutics, 12e YR 2015 FD 2015 PB McGraw-Hill Education PP New York, NY SN 9780071624428 LK accessmedicine.mhmedical.com/content.aspx?aid=1127869305 RD 2023/01/29 AB Thyroid hormone is essential for normal development, especially of the central nervous system (CNS). In the adult, thyroid hormone maintains metabolic homeostasis and influences the function of virtually all organ systems. Thyroid hormone contains iodine that must be supplied by nutritional intake. The thyroid gland contains large stores of thyroid hormone in the form of thyroglobulin. These stores maintain systemic concentrations of thyroid hormone despite variations in iodine availability and nutritional intake. The thyroidal secretion is predominantly the prohormone thyroxine, which is converted in the liver and other tissues to the active form, triiodothyronine. Local activation of thyroxine also occurs in target tissues (e.g., brain and pituitary) and is increasingly recognized as an important regulatory step in thyroid hormone action. Serum concentrations of thyroid hormones are precisely regulated by the pituitary hormone, thyrotropin (TSH), in a classic negative-feedback system. The predominant actions of thyroid hormone are mediated through binding to nuclear thyroid hormone receptors (TRs) and modulating transcription of specific genes. Thyroid hormones share a common mechanism of action with steroid and steroid-like hormones, such as vitamin D and the retinoids, whose receptors are members of a superfamily of nuclear receptors (Chapter 3). Although the predominant actions of thyroid hormone are nuclear, actions of thyroid hormone outside the nucleus have been reported.