THYROID STIMULATING HORMONE – THYROTROPIN
- It is a Glycoprotein hormone produced by basophil cells of anterior pituitary.
- Its mol. wt. is approx. 30,000. It consists of α and β subunits.
- The α-subunit of TSH, LH, hCG and FSH are nearly identical. The biological specificity of thyrotropin is in β-subunit
- The α-subunit – 92 amino acids while β-subunit has 112 (may vary in different books).
- Both α and β have several disulfide bridges.
- The carbohydrate content of TSH is about 21% & its α and β chains bear 2 & 1 oligosaccharide chains respectively, linked by N-glycosidic linkages to specific asparagine residues.
- The chains are synthesized separately by separate structural genes and later undergo post-translation modifications & glycosylations separately.
- TSH increases the secretion of thyroid hormones by stimulating all the steps of production of synthesis of thyroxine (Iodine uptake etc.).
- It acts through cAMP by binding with a receptor on thyroid cell surface.
- The TSH secretion is stimulated by TRH.
- The TRH also stimulates prolactin secretion.
- Whereas, the prolactin inhibitory factor (PIF) inhibits secretion of TSH to some extent.
- The TSH secretion is also controlled by …
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