Thyroid-Stimulating Hormone

Thyroid-stimulating hormone (TSH) is a glycoprotein produced by thyrotroph cells of the anterior pituitary gland, and consists of a heterodimer of two noncovalently linked subunits, α and β. Each subunit is encoded by a separate gene located on a different chromosome and is transcribed in a coordinated manner responsive mainly to stimulation by thyrotrophin-releasing hormone (TRH) and inhibition by thyroid hormone. Production of bioactive TSH involves a process of cotranslational glycosylation and folding that enables combination between the nascent α- and β-subunits. TSH is stored in secretory granules and released into the circulation in a regulated manner responsive mainly to stimulation by TRH. Circulating TSH binds to specific cell surface receptors in the thyroid gland where it stimulates the production of thyroid hormone, which modulates many metabolic processes and inhibits TSH production. Sensitive TSH assays allow accurate measurement of circulating TSH levels. Acquired and congenital disorders of TSH production are uncommon causes of abnormal thyroid gland function, but are important to recognize as a possible cause of abnormal thyroid function tests.