Thyroid-stimulating hormone (thyrotropin, TSH) is a glycoprotein hormone produced in the pituitary gland. TSH serves to stimulate the thyroid to produce thyroxine and its converted product triiodothyronine, which in turn stimulate metabolism throughout the body. High levels of TSH are secreted during stress, development and rapid growth. TSH is a heterodimer, and the beta subunit (TSHB) is unique to thyroid-stimulating hormone, while the alpha subunit (TSHA) is identical across chorionic gonadotropin, luteinizing hormone and follicle-stimulating hormone. Levels of TSH are commonly measured to determine degree of thyroid function and to diagnose diseases of the thyroid. In immunohistochemistry, antibodies to TSH are used to identify and subtype pituitary adenomas; roughly 1% of pituitary adenomas have been found to secrete excess TSH, which leads to downstream overproduction of thyroid hormones and consequently hyperthyroidism. In normal tissue, TSH has positive cytoplasmic staining in anterior pituitary endocrine cells. References: Clin Med Res. 2016 Jun;14(2):83-92, PMID: 27231117; J Endocrinol Invest. 2018 Apr;41(4):447-454, PMID: 29022276