Alpha-2 adrenergic receptor
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The α2 receptor is a type of adrenergic receptor.
Contents |
Effect
Edit
The α2 receptor has several, general, functions in common with other α-receptors, but also has individual effects.
GeneralEdit
Common (or still unspecified) effects include:
- Vasoconstriction of arteries to heart (coronary artery).[1]
- Vasoconstriction of veins[2]
- Decrease motility of smooth muscle in gastrointestinal tract[3]
- Contraction of male genitalia during ejaculation
IndividualEdit
Individual actions of the α2 receptor include:
- Mediates synaptic transmission in pre- and postsynaptic nerve terminals.
- Decrease release of acetylcholine[4]
- Decrease release of noradrenaline[4]
- Inhibit noradrenaline system in brain
- Inhibition[5] of lipolysis in adipose tissue.[6]
- inhibition of insulin release in pancreas.[6]
- induction of glucagon release from pancreas.
- platelet aggregation
- contraction of sphincters of the gastrointestinal tract
- ↓ Secretion from salivary gland[7]
MechanismEdit
A G protein - Gi renders adenylate cyclase inactivated, resulting in decrease of cAMP.
The relaxation of gastrointestinal tract motility is by presynaptic inhibition[4], where transmitters inhibit further release by homotropic effects.
AgonistsEdit
adrenaline has higher affinity for the alpha-2 receptor than has noradrenaline, which, in turn, has much higher affinity than has isoprenaline.[4] Other agonists include:
- clonidine*[4] (antihypertensive)
- lofexidine (antihypertensive)
- xylazine (veterinary)
- tizanidine (in spasms, cramping)
- guanfacine (antihypertensive)
- clenbuterol*[4] (decongestant and bronchodilator)
* denotes selective agonists to the receptor.
AntagonistsEdit
- yohimbine*[4] (purported aphrodisiac)
- mirtazapine (NaSSA)
- mianserin (tetracyclic antidepressant)
- idazoxan*[4](experimental)[8]
* denotes selective agonists to the receptor.
TypesEdit
There are three types of α2 receptors: ADRA2A, ADRA2B, ADRA2C.
See alsoEdit
- Other adrenergic receptors
ReferencesEdit
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Rang, H. P. (2003). Pharmacology, Edinburgh: Churchill Livingstone. Page 163
- ↑ 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.
- ↑ 6.0 6.1 Fitzpatrick, David; Purves, Dale; Augustine, George (2004). "Table 20:2" Neuroscience, Third Edition, Sunderland, Mass: Sinauer.
- ↑ Khan ZP, Ferguson CN, Jones RM (1999). alpha-2 and imidazoline receptor agonists. Their pharmacology and therapeutic role. Anaesthesia 54 (2): 146–65.
- ↑ online-medical-dictionary.org
{{enWP|Alpha-2 adrenergic receptor]]
