Alpha-1 adrenergic receptor

See also: Adrenergic receptor

The alpha-1 (α₁) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the G_q heterotrimeric G-protein. It consists of three highly homologous subtypes, including α_1A-, α_1B-, and α_1D-adrenergic. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α₁-adrenergic receptor in the central and peripheral nervous systems. There is no α_1C receptor. At one time, there was a subtype known as α_1C, but it was found to be identical to the previously discovered α_1A receptor subtype.^[1] To avoid confusion, naming was continued with the letter D.

Contents

• 
  1 Effects
  
  
  
  • 
    1.1 Smooth muscle
    
    
    
    • 
      1.1.1 Neuronal
      
    
    
    • 
      1.1.2 Other
      
    
    
    
    
  
  
  
  


• 
  2 Signaling cascade
  


• 
  3 Activity during exercise
  


• 
  4 Ligands
  


• 
  5 See also
  


• 
  6 References
  


• 
  7 External links
  

Effects

The α₁-adrenergic receptor has several general functions in common with the α₂-adrenergic receptor, but also has specific effects of its own. α1-receptors primarily mediate smooth muscle contraction, but have important functions elsewhere as well.^[2] The neurotransmitter norepinephrine has higher affinity for the α1 receptor than does epinephrine (which is a hormone).

Smooth muscle

In smooth muscle cells of blood vessels the principal effect of activation of these receptors is vasoconstriction. Blood vessels with α₁-adrenergic receptors are present in the skin, the sphincters^[3] of gastrointestinal system, kidney (renal artery)^[4] and brain.^[5] During the fight-or-flight response vasoconstriction results in decreased blood flow to these organs. This accounts for the pale appearance of the skin of an individual when frightened.

It also induces contraction of the urinary bladder,^[6][7] although this effect is minor compared to the relaxing effect of β₂-adrenergic receptors. In other words, the overall effect of sympathetic stimuli on the bladder is relaxation, in order to inhibit micturition upon anticipation of a stressful event. Other effects on smooth muscle are contraction in:

• Ureter


• 
  Uterus (when pregnant)


• Urethral sphincter


• 
  Bronchioles (although minor to the relaxing effect of β₂ receptor on bronchioles)


• 
  Iris dilator muscle^[3]
  


• 
  Seminal tract,^[3] resulting in ejaculation
  

Neuronal

Activation of α₁-adrenergic receptors produces anorexia and partially mediates the efficacy of appetite suppressants like phenylpropanolamine and amphetamine in the treatment of obesity.^[8] Norepinephrine has been shown to decrease cellular excitability in all layers of the temporal cortex, including the primary auditory cortex. In particular, norepinephrine decreases glutamatergic excitatory postsynaptic potentials by the activation of α₁-adrenergic receptors.^[9]
α1-adrenergic receptor subtypes increase inhibition in the olfactory system, suggesting a synaptic mechanism for noradrenergic modulation of olfactory driven behaviors.^[10]

Other

• Both positive and negative inotropic effects on heart muscle^[6][11]
  


• Secretion from salivary gland^[6]
  


• Increase salivary potassium levels


• 
  Glycogenolysis and gluconeogenesis in liver.


• Secretion from sweat glands^[6]
  


• Contraction of the urinary bladder urothelium and lamina propria ^[12]
  


• 
  Na⁺ reabsorption from kidney^[6]
  
  
  • Stimulate proximal tubule NHE3^[13]
    
  
  
  • Stimulate proximal tubule basolateral Na-K ATPase^[13]
    
  
  
  
  


• Activate mitogenic responses and regulate growth and proliferation of many cells


• Involved in the detection of mechanical feedback on the hypoglossal motor neurons which allow a long-term facilitation in respiration in response to repeated apneas.^[14]
  

Signaling cascade

α₁-Adrenergic receptors are members of the G protein-coupled receptor superfamily. Upon activation, a heterotrimeric G protein, G_q, activates phospholipase C (PLC), which causes an increase in IP₃ and calcium. While DAG stays near the membrane, IP3 diffuses into the cytosol and to find the IP3 receptor on the endoplasmic reticulum, triggering calcium release from the stores. This triggers further effects, primarily through the activation of an enzyme Protein Kinase C. This enzyme, as a kinase, functions by phosphorylation of other enzymes causing their activation, or by phosphorylation of certain channels leading to the increase or decrease of electrolyte transfer in or out of the cell.

Activity during exercise

During exercise, α₁-adrenergic receptors in active muscles are attenuated in an exercise intensity-dependent manner, allowing the β₂-adrenergic receptors which mediate vasodilation to dominate.^[15] In contrast to α₂-adrenergic receptors, α₁-adrenergic-receptors in the arterial vasculature of skeletal muscle are more resistant to inhibition, and attenuation of α1-adrenergic-receptor-mediated vasoconstriction only occurs during heavy exercise.^[15]

Note that only active muscle α₁-adrenergic receptors will be blocked. Resting muscle will not have its α₁-adrenergic receptors blocked, and hence the overall effect will be α₁-adrenergic-mediated vasoconstriction.^{[citation needed]}

Ligands

Main article: Alpha-1 blocker

Agonists Cirazoline (vasoconstrictor) Methoxamine (vasoconstrictor) Synephrine (mild vasoconstrictor) Etilefrine (antihypotensive) Metaraminol (antihypotensive) Midodrine (antihypotensive) Naphazoline (decongestant) Norepinephrine (vasoconstrictor) Oxymetazoline (decongestant) Phenylephrine (decongestant) Pseudoephedrine (decongestant) Tetrahydrozoline (decongestant) Xylometazoline (decongestant)

Antagonists Acepromazine (antipsychotic, secondary mechanism) Alfuzosin (used in benign prostatic hyperplasia) Arotinolol Carvedilol (used in congestive heart failure; it is a non-selective beta blocker) Doxazosin (used in hypertension and benign prostatic hyperplasia) Indoramin Labetalol (used in hypertension; it is a mixed alpha/beta adrenergic antagonist)[16] Moxisylyte Phenoxybenzamine Phentolamine (used in hypertensive emergencies; it is a nonselective alpha-antagonist) Prazosin (used in hypertension) Quetiapine Risperidone Silodosin Tamsulosin (used in benign prostatic hyperplasia) Terazosin Tiamenidine[17] Tolazoline Trazodone Trimazosin Urapidil

Various heterocyclic antidepressants and antipsychotics are α₁-adrenergic receptor antagonists as well. This action is generally undesirable in such agents and mediates side effects like orthostatic hypotension, and headaches due to excessive vasodilation.

See also

• Adrenergic receptor

References

1. 
   ^ Graham, Robert (May 1, 1996). "α1-Adrenergic Receptor Subtypes Molecular Structure, Function, and Signaling". Circulation Research. 78 (5): 737–749. doi:10.1161/01.RES.78.5.737. Retrieved 6 December 2016..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"""""""'""'"}.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
   


2. 
   ^ Piascik, M. T.; Perez, D. M. (2001). "Alpha1-adrenergic receptors: New insights and directions". The Journal of Pharmacology and Experimental Therapeutics. 298 (2): 403–10. PMID 11454900.
   


3. 
   ^ ^abc Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 163
   


4. 
   ^ Schmitz JM, Graham RM, Sagalowsky A, Pettinger WA (1981). "Renal α₁ and α₂ adrenergic receptors: biochemical and pharmacological correlations". J. Pharmacol. Exp. Ther. 219 (2): 400–6. PMID 6270306.
   


5. 
   ^ Circulation & Lung Physiology I M.A.S.T.E.R. Learning Program, UC Davis School of Medicine
   


6. 
   ^ ^abcde Fitzpatrick, David; Purves, Dale; Augustine, George (2004). "Table 20:2". Neuroscience (3rd ed.). Sunderland, Mass: Sinauer. ISBN 0-87893-725-0.
   


7. 
   ^ Chou EC, Capello SA, Levin RM, Longhurst PA (2003). "Excitatory α₁-adrenergic receptors predominate over inhibitory β-receptors in rabbit dorsal detrusor". J. Urol. 170 (6 Pt 1): 2503–7. doi:10.1097/01.ju.0000094184.97133.69. PMID 14634460.
   


8. 
   ^ Cheng JT, Kuo DY (2003). "Both alpha1-adrenergic and D(1)-dopaminergic neurotransmissions are involved in phenylpropanolamine-mediated feeding suppression in mice". Neuroscience Letters. 347 (2): 136–8. doi:10.1016/S0304-3940(03)00637-2. PMID 12873745.
   


9. 
   ^ Dinh, L; Nguyen T; Salgado H; Atzori M (2009). "Norepinephrine homogeneously inhibits alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate- (AMPAR-) mediated currents in all layers of the temporal cortex of the rat". Neurochem Res. 34 (11): 1896–906. doi:10.1007/s11064-009-9966-z. PMID 19357950.
   


10. 
    ^ Zimnik NC, Treadway T, Smith RS, Araneda RC (2013). "α(1A)-Adrenergic regulation of inhibition in the olfactory bulb". J. Physiol. 591 (Pt 7): 1631–43. doi:10.1113/jphysiol.2012.248591. PMC 3624843. PMID 23266935.
    


11. 
    ^ Wang, G. Y.; McCloskey, D. T.; Turcato, S; Swigart, P. M.; Simpson, P. C.; Baker, A. J. (2006). "Contrasting inotropic responses to alpha1-adrenergic receptor stimulation in left versus right ventricular myocardium". AJP: Heart and Circulatory Physiology. 291 (4): H2013–7. doi:10.1152/ajpheart.00167.2006. PMID 16731650.
    


12. 
    ^ Moro C, Tajouri L, Chess-Williams R (Jan 2013). "Adrenoceptor function and expression in bladder urothelium and lamina propria". Urology. 81 (1): 211.e1–7. doi:10.1016/j.urology.2012.09.011. PMID 23200975.
    


13. 
    ^ ^ab Walter F. Boron (2005). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 787
    


14. 
    ^ Tadjalli, Arash; Duffin, James; Peever, John (2010). "Identification of a novel form of noradrenergic-dependent respiratory motor plasticity triggered by vagal feedback". The Journal of Neuroscience. 30 (50): 16886–16895. doi:10.1523/JNEUROSCI.3394-10.2010. PMID 21159960.
    


15. 
    ^ ^ab http://jap.physiology.org/content/90/1/172.full
    


16. 
    ^ Fahed S, Grum DF, Papadimos TJ (2008). "Labetalol infusion for refractory hypertension causing severe hypotension and bradycardia: an issue of patient safety". Patient Saf Surg. 2: 13. doi:10.1186/1754-9493-2-13. PMC 2429901. PMID 18505576.
    


17. 
    ^ Timmermans, PB; de Jonge, A; Thoolen, MJ; Wilffert, B; Batink, H; van Zwieten, PA (April 1984). "Quantitative relationships between alpha-adrenergic activity and binding affinity of alpha-adrenoceptor agonists and antagonists". Journal of Medicinal Chemistry. 27 (4): 495–503. doi:10.1021/jm00370a011. PMID 6142954.
    

External links

• 
  "Adrenoceptors". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.
  

v t e Cell surface receptor: G protein-coupled receptors
Class A: Rhodopsin-like Neurotransmitter Adrenergic α1 (A B D) α2 (A B C) β1 β2 β3 Purinergic Adenosine (A1 A2A A2B A3) P2Y (1 2 4 5 6 8 9 10 11 12 13 14) Serotonin (all but 5-HT3) 5-HT1 (A B D E F) 5-HT2 (A B C) 5-HT (4 5A 6 7) Other Acetylcholine (M1 M2 M3 M4 M5) Dopamine D1 D2 D3 D4 D5 GHB receptor Histamine H1 H2 H3 H4 Melatonin (1A 1B 1C) TAAR (1 2 5 6 8 9) Metabolites and signaling molecules Eicosanoid CysLT (1 2) LTB4 1 2 FPRL1 OXE Prostaglandin DP (1 2), EP (1 2 3 4), FP Prostacyclin Thromboxane Other Bile acid Cannabinoid (CB1 CB2, GPR (18 55 119)) EBI2 Estrogen Free fatty acid (1 2 3 4) Hydroxycarboxylic acids 1 2 3 Lysophosphatidic acid (1 2 3 4 5 6) Lysophospholipid (1 2 3 4 5 6 7 8) Oxoglutarate PAF Sphingosine-1-phosphate (1 2 3 4 5) Succinate Peptide Neuropeptide B/W (1 2) FF (1 2) S Y (1 2 4 5) Neuromedin (B U (1 2)) Neurotensin (1 2) Other Anaphylatoxin (C3a C5a) Angiotensin (1 2) Apelin Bombesin BRS3 GRPR NMBR) Bradykinin (B1 B2) Chemokine Cholecystokinin (A B) Endothelin A B Formyl peptide (1 2 3) FSH Galanin (1 2 3) Gonadotropin-releasing hormone (1 2) Ghrelin Kisspeptin Luteinizing hormone/choriogonadotropin MAS (1 1L D E F G X1 X2 X3 X4) Melanocortin (1 2 3 4 5) MCHR (1 2) Motilin Opioid (Delta Kappa Mu Nociceptin & Zeta, but not Sigma) Orexin (1 2) Oxytocin Prokineticin (1 2) Prolactin-releasing peptide Relaxin (1 2 3 4) Somatostatin (1 2 3 4 5) Tachykinin (1 2 3) Thyrotropin Thyrotropin-releasing hormone Urotensin-II Vasopressin (1A 1B 2) Miscellaneous Orphan GPR (1 3 4 6 12 15 17 18 19 20 21 22 23 25 26 27 31 32 33 34 35 37 39 42 44 45 50 52 55 61 62 63 65 68 75 77 78 81 82 83 84 85 87 88 92 101 103 109A 109B 119 120 132 135 137B 139 141 142 146 148 149 150 151 152 153 160 161 162 171 173 174 176 177 182 183) Other Adrenomedullin Olfactory Opsin (3 4 5 1LW 1MW 1SW RGR RRH) Protease-activated (1 2 3 4) SREB (1 2 3)
Class B: Secretin-like Adhesion ADGRG (1 2 3 4 5 6 7) Orphan GPR (56 64 97 98 110 111 112 113 114 115 116 123 124 125 126 128 133 143 144 155 157) Other Brain-specific angiogenesis inhibitor (1 2 3) Cadherin (1 2 3) Calcitonin CALCRL CD97 Corticotropin-releasing hormone (1 2) EMR (1 2 3) Glucagon (GR GIPR GLP1R GLP2R) Growth-hormone-releasing hormone PACAPR1 GPR Latrophilin (1 2 3 ELTD1) Methuselah-like proteins Parathyroid hormone (1 2) Secretin Vasoactive intestinal peptide (1 2)
Class C: Metabotropic glutamate / pheromone Taste TAS1R (1 2 3) TAS2R (1 3 4 5 7 8 9 10 13 14 16 19 20 30 31 38 39 40 41 42 43 45 46 50 60 Vomeronasal receptor) Other Calcium-sensing receptor GABAB (1 2) Glutamate receptor (Metabotropic glutamate (1 2 3 4 5 6 7 8)) GPRC6A GPR (156 158 179) RAIG (1 2 3 4)
Class F: Frizzled & Smoothened Frizzled Frizzled (1 2 3 4 5 6 7 8 9 10) Smoothened Smoothened

v t e Adrenergic receptor modulators
α1	Agonists: 6-FNE Amidephrine Anisodine Buspirone Cirazoline Corbadrine Desglymidodrine Dexisometheptene Dipivefrine Dopamine Droxidopa (L-DOPS) Ephedrine Epinephrine Etilefrine Etilevodopa Ethylnorepinephrine Indanidine Isometheptene L-DOPA (levodopa) L-Phenylalanine L-Tyrosine Melevodopa Metaraminol Methoxamine Methyldopa Midodrine Naphazoline Norepinephrine Octopamine (drug) Oxymetazoline Phenylephrine Phenylpropanolamine Pseudoephedrine Synephrine Tetryzoline Tiamenidine XP21279 Xylometazoline Antagonists: Abanoquil Adimolol Ajmalicine Alfuzosin Amosulalol Anisodamine Arotinolol Atiprosin Atypical antipsychotics (e.g., brexpiprazole, clozapine, olanzapine, quetiapine, risperidone) Benoxathian Buflomedil Bunazosin Carvedilol Corynanthine Dapiprazole Domesticine Doxazosin Ergolines (e.g., ergotamine, dihydroergotamine, lisuride, terguride) Etoperidone Eugenodilol Fenspiride Hydroxyzine Indoramin Ketanserin L-765,314 Labetalol mCPP Mepiprazole Metazosin Monatepil Moxisylyte Naftopidil Nantenine Neldazosin Niaprazine Nicergoline Niguldipine Pardoprunox Pelanserin Perlapine Phendioxan Phenoxybenzamine Phentolamine Phenylpiperazine antidepressants (e.g., hydroxynefazodone, nefazodone, trazodone, triazoledione) Piperoxan Prazosin Quinazosin Quinidine Ritanserin Silodosin Spiperone Talipexole Tamsulosin Terazosin Tiodazosin Tolazoline Tetracyclic antidepressants (e.g., amoxapine, maprotiline, mianserin) Tricyclic antidepressants (e.g., amitriptyline, clomipramine, doxepin, imipramine, trimipramine) Trimazosin Typical antipsychotics (e.g., chlorpromazine, fluphenazine, loxapine, thioridazine) Urapidil WB-4101 Zolertine
α2	Agonists: (R)-3-Nitrobiphenyline 4-NEMD 6-FNE Amitraz Apraclonidine Brimonidine Cannabivarin Clonidine Corbadrine Detomidine Dexmedetomidine Dihydroergotamine Dipivefrine Dopamine Droxidopa (L-DOPS) Etilevodopa Ephedrine Ergotamine Epinephrine Etilefrine Ethylnorepinephrine Guanabenz Guanfacine Guanoxabenz L-DOPA (levodopa) L-Phenylalanine L-Tyrosine Lofexidine Medetomidine Melevodopa Methyldopa Mivazerol Naphazoline Norepinephrine Oxymetazoline Phenylpropanolamine Piperoxan Pseudoephedrine Rezatomidine Rilmenidine Romifidine Talipexole Tasipimidine Tetrahydrozoline Tiamenidine Tizanidine Tolonidine Urapidil Vatinoxan XP21279 Xylazine Xylometazoline Antagonists: 1-PP Adimolol Amesergide Aptazapine Atipamezole Atypical antipsychotics (e.g., asenapine, brexpiprazole, clozapine, lurasidone, paliperidone, quetiapine, risperidone, zotepine) Azapirones (e.g., buspirone, gepirone, ipsapirone, tandospirone) BRL-44408 Buflomedil Cirazoline Efaroxan Esmirtazapine Fenmetozole Fluparoxan Idazoxan mCPP Mianserin Mirtazapine NAN-190 Olanzapine Pardoprunox Phentolamine Phenoxybenzamine Piperoxan Piribedil Rauwolscine Rotigotine SB-269970 Setiptiline Spiroxatrine Sunepitron Tolazoline Typical antipsychotics (e.g., chlorpromazine, fluphenazine, loxapine, thioridazine) Yohimbine
β	Agonists: Abediterol Alifedrine Amibegron Arbutamine Arformoterol Arotinolol BAAM Bambuterol Befunolol Bitolterol Broxaterol Buphenine Carbuterol Carmoterol Cimaterol Clenbuterol Colterol Corbadrine Denopamine Dipivefrine Dobutamine Dopamine Dopexamine Droxidopa (L-DOPS) Ephedrine Epinephrine Etafedrine Etilefrine Etilevodopa Ethylnorepinephrine Fenoterol Formoterol Hexoprenaline Higenamine Indacaterol Isoetarine Isoprenaline Isoxsuprine L-DOPA (levodopa) L-Phenylalanine L-Tyrosine Levosalbutamol Mabuterol Melevodopa Methoxyphenamine Methyldopa Mirabegron Norepinephrine Orciprenaline Oxyfedrine PF-610355 Phenylpropanolamine Pirbuterol Prenalterol Ractopamine Procaterol Pseudoephedrine Reproterol Rimiterol Ritodrine Salbutamol Salmeterol Solabegron Terbutaline Tretoquinol Tulobuterol Vilanterol Xamoterol XP21279 Zilpaterol Zinterol Antagonists: Acebutolol Adaprolol Adimolol Afurolol Alprenolol Alprenoxime Amosulalol Ancarolol Arnolol Arotinolol Atenolol Befunolol Betaxolol Bevantolol Bisoprolol Bopindolol Bornaprolol Brefonalol Bucindolol Bucumolol Bufetolol Bufuralol Bunitrolol Bunolol Bupranolol Butaxamine Butidrine Butofilolol Capsinolol Carazolol Carpindolol Carteolol Carvedilol Celiprolol Cetamolol Cicloprolol Cinamolol Cloranolol Cyanopindolol Dalbraminol Dexpropranolol Diacetolol Dichloroisoprenaline Dihydroalprenolol Dilevalol Diprafenone Draquinolol Ecastolol Epanolol Ericolol Ersentilide Esatenolol Esprolol Eugenodilol Exaprolol Falintolol Flestolol Flusoxolol Hydroxycarteolol Hydroxytertatolol ICI-118,551 Idropranolol Indenolol Indopanolol Iodocyanopindolol Iprocrolol Isoxaprolol Isamoltane Labetalol Landiolol Levobetaxolol Levobunolol Levomoprolol Medroxalol Mepindolol Metipranolol Metoprolol Moprolol Nadolol Nadoxolol Nebivolol Nifenalol Nipradilol Oxprenolol Pacrinolol Pafenolol Pamatolol Pargolol Penbutolol Pindolol Practolol Primidolol Procinolol Pronethalol Propafenone Propranolol Ridazolol Ronactolol Soquinolol Sotalol Spirendolol SR 59230A Sulfinalol Talinolol Tazolol Tertatolol Tienoxolol Tilisolol Timolol Tiprenolol Tolamolol Toliprolol Xibenolol Xipranolol

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