Thyroid-stimulating hormone (TSH, thyrotropin) is a dimeric glycoprotein synthesized and secreted by thyrotrope cells in the anterior pituitary gland. TSH regulates the endocrine function of the thyroid gland, mediating the release of the hormones thyroxine (T4) and triiodothyronine (T3).
Thyrostimulin is a dimer of Glycoprotein hormone alpha-2 (GPHA2) and Glycoprotein hormone beta-5(GPHB5), comprising the a fifth glycoprotein hormone (Nakabayashi et al. 2002), a more potent ligand for the TSH receptor than TSH which has a wider tissue distribution (Huang et al. 2016).
These effects are mediated by the TSH receptor (Nagayama Y et al, 1989), found primarily on thyroid follicular cells. The activated receptor couples with the G protein alpha-s subunit (Allgeier A et al 1994) which activates adeylate cyclase and increases intracellular cAMP levels.