Thyrotropin

Synonyms: TSH, hTSH, TSH 1, Thyreotropin, thyroid stimulating hormone, thyrotropic hormone
German: Thyrotropin

1 Definition

The thyroid stimulating hormone is a peptide hormone that is produced and secreted by the anterior lobe of the pituitary gland. It induces an increased synthesis of thyroid hormones by the thyroid gland. Reciprocally, the secretion of thyroid-stimulating hormones is inhibited by thyroid hormones (thyrotropic feedback control).

2 Structure

The hormone TSH is a glycoprotein consisting of two subunits. It has a shared alpha-subunit with HCG, FSH and LH. The beta subunit conveys the hormone specific signal. Thyrostimulin (TSH 2, A2B5), a related glycoprotein that also has a thyroid stimulating effect, has and additional second alpha-subunit and a fifth beta-subunit.

3 Physiology

The following factors influence secretion of TSH:

3.1 Stimulating factors

• TRH
• Neurotensin
• ADH

3.2 Inhibiting factors

• Thyroxin (T4) and triiodothyronine (T3)
• SIH
• Dopamine
• TSH
• Thyrostimulin (TSH 2)
• Cytokines (presumably)

3.3 Mechanism of action

TSH binds to heptahelical receptors located on the surface of thyroid cells. This leads to an increase in the intracellular concentration of cAMP via stimulation through [G protein|[G proteins]]. The result is a significant increase of synthesis and secretion of T4. To a lesser extent, an increased cAMP concentration within thyrocytes also stimulates the intrathyroidal deiodation. This has the effect that in case of hypothyroidism the sum activity of peripheral deiodinases is increased and results in a redundant compensatory regulation in the early stages of thyroid deficiency.^[1]

4 Literature

1. ↑ Hoermann R, Midgley JE, Larisch R, Dietrich JW. Is pituitary TSH an adequate measure of thyroid hormone-controlled homoeostasis during thyroxine treatment? Eur J Endocrinol. 2013 Jan 17;168(2):271-80. doi: 10.1530/EJE-12-0819. Print 2013 Feb. PMID 23184912.