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Alpha-2 adrenergic receptor: Wikis


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The alpha-2 (α2) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including α2A-, α2B-, and α2C-adrenergic. Some species other than humans express a fourth α2D-adrenergic receptor as well.[1] Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α2-adrenergic receptor in the central and peripheral nervous systems.



The α2-adrenergic receptor has several general functions in common with the α1-adrenergic receptor, but also has specific effects of its own.


Common (or still unspecified) effects include:


Individual actions of the α2 receptor include:

Signaling cascade

The alpha subunit of an inhibitory G protein - Gi dissociated from the G protein, and associates with adenyl cyclase (also known as adenylate cyclase or adenylyl cyclase). This causes the inactivation of adenyl cyclase, resulting in a decrease of cAMP produced from ATP. This leads to a decrease of intracellular cAMP. Protein Kinase A is not able to be activated by cAMP, and so phosphorylase kinase cannot be phosphorylated by PKA. Phosphorylase kinase is responsible for the phosphorylation of proteins, and so there is a decrease in the levels of phosphorylated proteins, and the eventual cell response is decreased.

The relaxation of gastrointestinal tract motility is by presynaptic inhibition[6], where transmitters inhibit further release by homotropic effects.


See also


  1. ^ Ruuskanen JO, Xhaard H, Marjamäki A, Salaneck E, Salminen T, Yan YL, Postlethwait JH, Johnson MS, Larhammar D, Scheinin M (January 2004). "Identification of duplicated fourth alpha2-adrenergic receptor subtype by cloning and mapping of five receptor genes in zebrafish". Molecular Biology and Evolution 21 (1): 14–28. doi:10.1093/molbev/msg224. PMID 12949138. 
  2. ^ Goodman Gilman, Alfred. Goodman & Gilman's The Pharmacological Basis of Therapeutics. Tenth Edition. McGraw-Hill (2001): Page 140.
  3. ^ Woodman OL, Vatner SF (1987). "Coronary vasoconstriction mediated by α1- and α2-adrenoceptors in conscious dogs". Am. J. Physiol. 253 (2 Pt 2): H388–93. PMID 2887122. 
  4. ^ Elliott J (1997). "Alpha-adrenoceptors in equine digital veins: evidence for the presence of both α1 and α2-receptors mediating vasoconstriction". J. Vet. Pharmacol. Ther. 20 (4): 308–17. doi:10.1046/j.1365-2885.1997.00078.x. PMID 9280371. 
  5. ^ Sagrada A, Fargeas MJ, Bueno L (1987). "Involvement of α1 and α2 adrenoceptors in the postlaparotomy intestinal motor disturbances in the rat". Gut 28 (8): 955–9. doi:10.1136/gut.28.8.955. PMID 2889649. 
  6. ^ a b c Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4.  Page 163
  7. ^ Wright EE, Simpson ER (1981). "Inhibition of the lipolytic action of beta-adrenergic agonists in human adipocytes by alpha-adrenergic agonists". J. Lipid Res. 22 (8): 1265–70. PMID 6119348. 
  8. ^ a b Fitzpatrick, David; Purves, Dale; Augustine, George (2004). "Table 20:2". Neuroscience (Third ed.). Sunderland, Mass: Sinauer. ISBN 0-87893-725-0. 
  9. ^ Khan ZP, Ferguson CN, Jones RM (1999). "alpha-2 and imidazoline receptor agonists. Their pharmacology and therapeutic role". Anaesthesia 54 (2): 146–65. doi:10.1046/j.1365-2044.1999.00659.x. PMID 10215710. 

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