Molecular biology of thyrotropin.

Abstract

Introduction THE pituitary glycoprotein hormone TSH is synthesized and secreted by the thyrotropes in the anterior pituitary. TSH acts on the thyroid gland to increase the production of the thyroid hormones T3 and T4, which then act on organs throughout the body to modulate growth and various metabolic processes. High levels of the thyroid hormones in turn feed back at the level of the pituitary to suppress synthesis and secretion of TSH, and the thyroid hormone concentration is the most important physiological regulator of TSH levels (1–5). Additional regulation can occur via hypothalamic hormones such as TRH and dopamine, which stimulate and suppress TSH levels, respectively (1, 2) (Fig. 1). Thyroid and hypothalamic hormones interact to modulate both circulating levels of TSH and the transcription of the genes encoding the hormone. TSH is one of three pituitary glycoprotein hormones that consists of two dissimilar noncovalent subunits, α and β. The α-subunit is common to all three, including TSH and the...