- Alpha-1 adrenergic receptor
The alpha-1 adrenergic receptor (α1-AR) is an
adrenergic receptorwith the primary effect of vasoconstriction.
The α1 receptor has several, general, functions in common with other α-receptors, but also has specific effects.
Common (or still unspecified) effects include:
Vasoconstrictionof arteriesto heart( coronary arteries).cite journal | author = Woodman OL, Vatner SF | title = Coronary vasoconstriction mediated by α1- and α2-adrenoceptors in conscious dogs | journal = Am. J. Physiol. | volume = 253 | issue = 2 Pt 2 | pages = H388–93 | year = 1987 | pmid = 2887122 | doi = | issn = | url = http://ajpheart.physiology.org/cgi/content/abstract/253/2/H388 ]
* Venoconstriction of
veinscite journal | author = Elliott J | title = Alpha-adrenoceptors in equine digital veins: evidence for the presence of both α1 and α2-receptors mediating vasoconstriction | journal = J. Vet. Pharmacol. Ther. | volume = 20 | issue = 4 | pages = 308–17 | year = 1997 | pmid = 9280371 | doi = 10.1046/j.1365-2885.1997.00078.x | issn = ]
* Decrease motility of
smooth musclein gastrointestinal tractcite journal | author = Sagrada A, Fargeas MJ, Bueno L | title = Involvement of α1 and α2 adrenoceptors in the postlaparotomy intestinal motor disturbances in the rat | journal = Gut | volume = 28 | issue = 8 | pages = 955–9 | year = 1987 | pmid = 2889649 | doi = 10.1136/gut.28.8.955 | issn = ]
The primary effect is on
smooth muscle, which mainly constrict. However, there are other functions as well.
In smooth muscle of
blood vessels the principal effect is vasoconstriction. Blood vessels with α1 receptors are present in the skin, the sphinctersof gastrointestinal system, kidney( renal artery)cite journal | author = Schmitz JM, Graham RM, Sagalowsky A, Pettinger WA | title = Renal α1 and α2 adrenergic receptors: biochemical and pharmacological correlations | journal = J. Pharmacol. Exp. Ther. | volume = 219 | issue = 2 | pages = 400–6 | year = 1981 | pmid = 6270306 | doi = | issn = | url = http://jpet.aspetjournals.org/cgi/content/abstract/219/2/400 ] and brain. [ [http://cim.ucdavis.edu/masters/sessions2002/session4_ica.doc Circulation & Lung Physiology I] M.A.S.T.E.R. Learning Program, UC Davis School of Medicine] During the fight-or-flight responsevasoconstriction results in the decreased blood flow to these organs. This accounts for an individual's skin appearing pale when frightened.
It also induces contraction of the
urinary bladdercite book | author = Fitzpatrick, David; Purves, Dale; Augustine, George | title = Neuroscience | publisher = Sinauer | location = Sunderland, Mass | year = 2004 | | edition = Third Edition | chapter = Table 20:2 | pages = | isbn = 0-87893-725-0 | oclc = | doi = ] cite journal | author = Chou EC, Capello SA, Levin RM, Longhurst PA | title = Excitatory α1-adrenergic receptors predominate over inhibitory β-receptors in rabbit dorsal detrusor | journal = J. Urol. | volume = 170 | issue = 6 Pt 1 | pages = 2503–7 | year = 2003 | pmid = 14634460 | doi = 10.1097/01.ju.0000094184.97133.69 | issn = ] , although this effect is minor compared to the relaxing effect of β-2 adrenergic receptors. In other words, the overall effect of sympathetic stimuli on the bladder is relaxation, in order to delay micturitionduring stress.
Other effects are on smooth muscle are contraction in:
hairs ( arrector pili muscles)
bronchioles(although minor to the relaxing effect of β2 receptor on bronchioles)
iris dilator musclecite book |author=Rang, H. P. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |pages= |isbn=0-443-07145-4 |oclc= |doi= Page 163 ]
seminal tract, resulting in ejaculation
In a few areas the result on smooth muscle is relaxation. These include:
*The rest of the GI tract than the sphincters.
*Blood vessels of
erectile tissue.cite journal | author = Morton JS, Daly CJ, Jackson VM, McGrath JC | title = Alpha1A-adrenoceptors mediate contractions to phenylephrine in rabbit penile arteries | journal = Br. J. Pharmacol. | volume = 150 | issue = 1 | pages = 112–20 | year = 2007 | pmid = 17115072 | doi = 10.1038/sj.bjp.0706956 | issn = ]
ionotropic effecton heart muscle. (α1<<β1).
Glycogenolysisand gluconeogenesisfrom adipose tissueand liver.
*Na+ reabsorption from
proximal tubule NHE3cite book |author=Walter F., PhD. Boron |title=Medical Physiology: A Cellular And Molecular Approaoch |publisher=Elsevier/Saunders |location= |year= |pages= |isbn=1-4160-2328-3 |oclc= |doi= Page 787 ]
proximal tubulebasolateral Na-K ATPase
mitogenicresponses and regulate growth and proliferation of many cells.
Activity During Exercise
During exercise these alpha-1 receptors can be selectively blocked by sympathetic nervous activity, allowing the beta-2 receptors (which mediate vasodilation) to dominate. Note that only the alpha-1 receptors in exercising muscle will be blocked. Resting muscle will not have its alpha-1 receptors blocked, and hence the overall effect there will be alpha-1 mediated vasocontriction.
Alpha1-adrenergic receptors are members of the
G protein-coupled receptorsuperfamily. Upon activation, a heterotrimeric G protein, Gq, activates phospholipase C(PLC), which causes an increase in IP3 and calcium. This triggers all other effects.
phenylephrine* ( decongestant)
cirazoline* *denotes selective agonists to the receptor.
Noradrenaline has higher
receptor affinitythan has adrenaline, which, in turn has much higher affinity than isoprenaline.
Antagonists are various "
phentolamine(in hypertensive emergencies)
prazosin* (in hypertension)
terazosin(in BPH and hypertension)
doxazocin* (in BPH and hypertension) *denotes selective antagonists to the receptor.
There are 3 α1-AR subtypes:
alpha-1A, -1B and -1D, all of which signal through the Gq/11 family of G-proteins and different subtypes show different patterns of activation.
Alpha-2 adrenergic receptor
Beta-1 adrenergic receptor
Beta-2 adrenergic receptor
Beta-3 adrenergic receptor
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