Thyrotropin

Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesised and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.

Physiology
The hypothalamus produces thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release TSH. TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). The production of TSH is inhibited by the production of somatostatin by the hypothalamus. T3 and T4 also inhibit TSH production and secretion, creating a regulatory negative feedback loop.TSH consists of two subunits, the alpha and the beta subunit. The &alpha; (alpha) subunit is identical to that of human chorionic gonadotropin (HCG), luteinising hormone (LH), follicle-stimulating hormone (FSH). All four glycoprotein hormones are produced in the anterior pituitary. The &beta; (beta) subunit is unique to TSH, and therefore determines its function. The TSH receptor is found mainly on thyroid follicular cells. Stimulating antibodies to this receptor mimic TSH action and are found in Graves' disease.

Genetics
The alpha chain is located on chromosome 6q12-21. The beta chain is located on chromosome 1p13.

Diagnostic use
TSH levels are tested in patients suspected of thyroid disease. Higher than normal levels of TSH may indicate congenital hypothyroidism (cretinism), hypothyroidism or thyroid hormone resistance. Lower than normal (suppressed) levels of TSH may indicate hyperthyroidism. Generally, a normal range for TSH is between .3 and 3.0 mIU/mL.