Adrenergic receptor
Encyclopedia
The adrenergic receptors (or adrenoceptors) are a class of metabotropic G protein-coupled receptor
s that are targets of the catecholamine
s, especially noradrenaline (norepinephrine) and adrenaline (epinephrine).
Although dopamine
is a catecholamine, its receptors are in a different category.
Many cells possess these receptors, and the binding of an agonist
will generally cause a sympathetic (or sympathomimetic) response (e.g. the fight-or-flight response
). For instance, the heart rate
will increase and the pupil
s will dilate, energy will be mobilized, and blood flow diverted from other non-essential organs to skeletal muscle
.
†There is no α1C receptor. At one time, there was a subtype known as C, but was found to be identical to one of the previously discovered subtypes. To avoid confusion, naming was continued with the letter D.
). The PLC cleaves phosphatidylinositol 4,5-bisphosphate
(PIP2), which in turn causes an increase in inositol triphosphate
(IP3) and diacylglycerol (DAG). The former interacts with calcium channels of endoplasmic and sarcoplasmic reticulum, thus changing the calcium content in a cell. This triggers all other effects.
Specific actions of the α1 receptor mainly involve smooth muscle contraction. It causes vasoconstriction
in many blood vessels, including those of the skin
, gastrointestinal system, kidney
(renal artery
) and brain
. Other areas of smooth muscle contraction are:
Further effects include glycogenolysis
and gluconeogenesis
from adipose tissue
and liver
, as well as secretion from sweat gland
s and Na+
reabsorption from kidney
.
Antagonists may be used in hypertension
.
Specific actions of the α2 receptor include:
G protein-coupled receptor
G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...
s that are targets of the catecholamine
Catecholamine
Catecholamines are molecules that have a catechol nucleus consisting of benzene with two hydroxyl side groups and a side-chain amine. They include dopamine, as well as the "fight-or-flight" hormones adrenaline and noradrenaline released by the adrenal medulla of the adrenal glands in response to...
s, especially noradrenaline (norepinephrine) and adrenaline (epinephrine).
Although dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
is a catecholamine, its receptors are in a different category.
Many cells possess these receptors, and the binding of an agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...
will generally cause a sympathetic (or sympathomimetic) response (e.g. the fight-or-flight response
Fight-or-flight response
The fight-or-flight response was first described by Walter Bradford Cannon....
). For instance, the heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
will increase and the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s will dilate, energy will be mobilized, and blood flow diverted from other non-essential organs to skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
.
Subtypes
There are two main groups of adrenergic receptors, α and β, with several subtypes.- α receptors have the subtypes α1Alpha-1 adrenergic receptorThe alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...
(a GqG proteinG proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...
coupled receptor) and α2Alpha-2 adrenergic receptorThe alpha-2 adrenergic receptor is a G protein-coupled receptor 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...
(a Gi coupled receptor). PhenylephrinePhenylephrinePhenylephrine is a selective α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure...
is a selective agonist of the α receptor. - β receptors have the subtypes β1Beta-1 adrenergic receptorThe beta-1 adrenergic receptor , also known as ADRB1, is a beta-adrenergic receptor, and also denotes the human gene encoding it...
, β2Beta-2 adrenergic receptorThe beta-2 adrenergic receptor , also known as ADRB2, is a beta-adrenergic receptor, and also denotes the human gene encoding it.-Gene:The gene is intronless...
and β3Beta-3 adrenergic receptorThe beta-3 adrenergic receptor , also known as ADRB3, is an beta-adrenergic receptor, and also denotes the human gene encoding it.-Function:Actions of the β3 receptor include:*Enhancement of lipolysis in adipose tissue....
. All three are linked to Gs proteins (although β2Beta-2 adrenergic receptorThe beta-2 adrenergic receptor , also known as ADRB2, is a beta-adrenergic receptor, and also denotes the human gene encoding it.-Gene:The gene is intronless...
also couples to Gi), which in turn are linked to adenylate cyclaseAdenylate cyclaseAdenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
. Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP. Downstream effectors of cAMP include cAMP-dependent protein kinaseCAMP-dependent protein kinaseIn cell biology, Protein kinase A refers to a family of enzymes whose activity is dependent on cellular levels of cyclic AMP . PKA is also known as cAMP-dependent protein kinase...
(PKA), which mediates some of the intracellular events following hormone binding. Isoprenaline is a selective agonist.
Roles in circulation
Adrenaline reacts with both α- and β-adrenoreceptors, causing vasoconstriction and vasodilation, respectively. Although α receptors are less sensitive to epinephrine, when activated, they override the vasodilation mediated by β-adrenoreceptors. The result is that high levels of circulating epinephrine cause vasoconstriction. At lower levels of circulating epinephrine, β-adrenoreceptor stimulation dominates, producing an overall vasodilation.Comparison
Smooth muscle behavior is variable depending on anatomical location. Smooth muscle contraction/relaxation is generalized below. One important note is the differential effects of increased cAMP in smooth muscle compared to cardiac muscle. Increased cAMP will promote relaxation in smooth muscle, while promoting increased contractility and pulse rate in cardiac muscle.| Receptor | Agonist potency order | Selected action of agonist Agonist An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance... |
Mechanism Second messenger system Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus. They relay the signals of hormones like epinephrine , growth factors, and others, and cause some kind of change in the activity of the cell... |
Agonists | Antagonists Adrenergic antagonist An Adrenergic antagonist is a pharmaceutical substance that acts to inhibit the action of the adrenergic receptors. It is thus a type of sympatholytic.It has the opposite effect as adrenergic agonists.More specifically, they can be divided into:... |
|---|---|---|---|---|---|
| α1 Alpha-1 adrenergic receptor The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic... : A Alpha-1A adrenergic receptor The alpha-1A adrenergic receptor , also known as ADRA1A, formerly known as the alpha-1C adrenergic receptor, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it.-Agonists:... , B Alpha-1B adrenergic receptor The alpha-1B adrenergic receptor , also known as ADRA1B, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it.-Interactions:... , D Alpha-1D adrenergic receptor The alpha-1D adrenergic receptor , also known as ADRA1D, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it.-Further reading:... † |
Norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... > epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... >> isoprenaline |
Smooth muscle Smooth muscle Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by... contraction |
Gq Gq alpha subunit Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway... : phospholipase C Phospholipase C Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in... (PLC) activated, IP3,and DAG, rise in calcium Calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust... |
(Alpha-1 agonists)
|
(Alpha-1 blockers)
Alfuzosin Alfuzosin is an α1 receptor antagonist used to treat benign prostatic hyperplasia . It works by relaxing the muscles in the prostate and bladder neck, making it easier to urinate.... Doxazosin Doxazosin mesylate, a quinazoline compound sold by Pfizer under the brand names Cardura and Carduran, is an α1a-selective alpha blocker used to treat high blood pressure and urinary retention associated with benign prostatic hyperplasia .... Phenoxybenzamine Phenoxybenzamine is a non-selective, irreversible alpha antagonist.-Uses:It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma... Phentolamine Phentolamine is a reversible nonselective alpha-adrenergic antagonist. -Mechanism:Its primary action is vasodilation due to α1 blockade.... Prazosin Prazosin, trade names Minipress, Vasoflex, Pressin and Hypovase, is a sympatholytic drug used to treat high blood pressure and Anxiety, PTSD and Panic Disorder. It belongs to the class of alpha-adrenergic blockers. Specifically, prazosin is selective for the alpha-1 receptors on vascular smooth... Tamsulosin Tamsulosin is an α1a-selective alpha blocker used in the symptomatic treatment of benign prostatic hyperplasia . Tamsulosin was developed by Yamanouchi Pharmaceuticals and is marketed by various companies under licence, including Boehringer-Ingelheim and CSL... Terazosin Terazosin is a selective alpha 1 antagonist used for treatment of symptoms of an enlarged prostate... (TCA:s Tricyclic antidepressant Tricyclic antidepressants are heterocyclic chemical compounds used primarily as antidepressants. The TCAs were first discovered in the early 1950s and were subsequently introduced later in the decade; they are named after their chemical structure, which contains three rings of atoms... )
|
| α2 Alpha-2 adrenergic receptor The alpha-2 adrenergic receptor is a G protein-coupled receptor 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... : A Alpha-2A adrenergic receptor The alpha-2A adrenergic receptor , also known as ADRA2A, is an alpha-2 adrenergic receptor, and also denotes the human gene encoding it.-Role in Central Nervous System:... , B Alpha-2B adrenergic receptor The alpha-2B adrenergic receptor , is a G-protein coupled receptor. It is a subtype of the adrenergic receptor family. The human gene encoding this receptor has the symbol ADRA2B.ADRA2B orthologs have been identified in several mammals.... , C Alpha-2C adrenergic receptor The alpha-2C adrenergic receptor , also known as ADRA2C, is an alpha-2 adrenergic receptor, and also denotes the human gene encoding it.-Agonists:* -3-Nitrobiphenyline -Antagonists:... |
Epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... ≥ norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... >> isoprenaline |
Smooth muscle Smooth muscle Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by... mixed effects and neurotransmitter inhibition & Cardiac muscle Cardiac muscle Cardiac muscle is a type of involuntary striated muscle found in the walls and histologic foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle... relaxation platelet Platelet Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days... activation |
Gi Gi alpha subunit Gi alpha subunit is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.- Receptors :The following G protein-coupled receptors couple to the Gi subunit:* Acetylcholine M2 & M4 receptors... : adenylate cyclase Adenylate cyclase Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell .... inactivated, cAMP Cyclic adenosine monophosphate Cyclic adenosine monophosphate is a second messenger important in many biological processes... down |
(Alpha-2 agonists)
|
(Alpha-2 blocker Alpha-2 blocker Although alpha blocker generally refers to α1-blockers, there are also α2-blockers, which are antagonists to the α2 adrenergic receptor. They are mainly used in research, finding little clinical application in human medicine, although yohimbine was previously used as an aphrodisiac, and is still... s) Phentolamine Phentolamine is a reversible nonselective alpha-adrenergic antagonist. -Mechanism:Its primary action is vasodilation due to α1 blockade.... Yohimbine Yohimbine is an alkaloid with stimulant and aphrodisiac effects found naturally in Pausinystalia yohimbe . It is also found naturally in Rauwolfia serpentina , Alchornea floribunda , along with several other active alkaloids... Idazoxan Idazoxan is a drug which is used in scientific research. It acts as both a selective α2 adrenergic receptor antagonist, and an antagonist for the imidazoline receptor. Idazoxan has been under investigation as an antidepressant, but it did not reach the market as such. More recently, it is under... Atipamezole Atipamezole is a synthetic alpha2-adrenergic antagonist, indicated for the reversal of the sedative and analgesic effects of dexmedetomidine and medetomidine in dogs. It has also been researched in humans as a potential anti-Parkinsonian drug.-External links:*... |
| β1 Beta-1 adrenergic receptor The beta-1 adrenergic receptor , also known as ADRB1, is a beta-adrenergic receptor, and also denotes the human gene encoding it... |
Isoprenaline > epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... = norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... |
Heart muscle contraction | Gs Gs alpha subunit The Gs alpha subunit is a heterotrimeric G protein subunit that activates the cAMP-dependent pathway by activating adenylate cyclase.-Receptors:The G protein-coupled receptors that couple to this kind of G-protein include:... : adenylate cyclase Adenylate cyclase Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell .... activated, cAMP Cyclic adenosine monophosphate Cyclic adenosine monophosphate is a second messenger important in many biological processes... up |
Dobutamine Dobutamine is a sympathomimetic drug used in the treatment of heart failure and cardiogenic shock. Its primary mechanism is direct stimulation of β1 receptors of the sympathetic nervous system. Dobutamine was developed by a laboratory led by Drs... |
(Beta blocker Beta blocker Beta blockers or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications. They are particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction ,... s)
|
| β2 Beta-2 adrenergic receptor The beta-2 adrenergic receptor , also known as ADRB2, is a beta-adrenergic receptor, and also denotes the human gene encoding it.-Gene:The gene is intronless... |
Isoprenaline > epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... >> norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... |
Smooth muscle Smooth muscle Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by... relaxation |
Gs Gs alpha subunit The Gs alpha subunit is a heterotrimeric G protein subunit that activates the cAMP-dependent pathway by activating adenylate cyclase.-Receptors:The G protein-coupled receptors that couple to this kind of G-protein include:... : adenylate cyclase Adenylate cyclase Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell .... activated, cAMP Cyclic adenosine monophosphate Cyclic adenosine monophosphate is a second messenger important in many biological processes... up (also Gi Gi alpha subunit Gi alpha subunit is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.- Receptors :The following G protein-coupled receptors couple to the Gi subunit:* Acetylcholine M2 & M4 receptors... , see β2 Beta-2 adrenergic receptor The beta-2 adrenergic receptor , also known as ADRB2, is a beta-adrenergic receptor, and also denotes the human gene encoding it.-Gene:The gene is intronless... ) |
(Short/long Beta2-adrenergic receptor agonist β2-adrenergic agonists, also known as β2-adrenergic receptor agonists, are a class of drugs used to treat asthma and other pulmonary disease states.-Uses:... ) Salbutamol Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names.... (Albuterol in USA) Formoterol Formoterol or eformoterol is a long-acting β2-agonist used in the management of asthma and/or chronic obstructive pulmonary disease... Levalbuterol Levosalbutamol or levalbuterol , trade name Xopenex, is the R-enantiomer of the short-acting β2-adrenergic receptor agonist salbutamol. It is marketed by Cipla as Levolin, & by axa named Axazest.-Uses:... Salmeterol Salmeterol is a long-acting beta2-adrenergic receptor agonist drug that is currently prescribed for the treatment of asthma and chronic obstructive pulmonary disease. It is currently available as a dry powder inhaler that releases a powdered form of the drug... Terbutaline Terbutaline is a β2-adrenergic receptor agonist.Terbutaline is currently on the World Anti-Doping Agency's list of prohibited drugs for Olympic athletes, except when administered by inhalation and a Therapeutic Use Exemption has been obtained in advance.Terbutaline is currently used to delay... Ritodrine Ritodrine is a tocolytic drug, was used to stop premature labor. It is available in oral tablets or as an injection, and is typically used as the hydrochloride salt, ritodrine hydrochloride... |
(Beta blocker Beta blocker Beta blockers or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications. They are particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction ,... s) |
| β3 Beta-3 adrenergic receptor The beta-3 adrenergic receptor , also known as ADRB3, is an beta-adrenergic receptor, and also denotes the human gene encoding it.-Function:Actions of the β3 receptor include:*Enhancement of lipolysis in adipose tissue.... |
Isoprenaline = norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... > epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... |
Enhance lipolysis Lipolysis Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver... , promotes relaxation of detrusor muscle in the bladder Bladder Bladder usually refers to an anatomical hollow organBladder may also refer to:-Biology:* Urinary bladder in humans** Urinary bladder ** Bladder control; see Urinary incontinence** Artificial urinary bladder, in humans... |
Gs Gs alpha subunit The Gs alpha subunit is a heterotrimeric G protein subunit that activates the cAMP-dependent pathway by activating adenylate cyclase.-Receptors:The G protein-coupled receptors that couple to this kind of G-protein include:... : adenylate cyclase Adenylate cyclase Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell .... activated, cAMP Cyclic adenosine monophosphate Cyclic adenosine monophosphate is a second messenger important in many biological processes... up |
Amibegron Amibegron is a drug developed by Sanofi-Aventis which acts as a selective agonist for the β3 adrenergic receptor. It is the first orally active β3 agonist developed that is capable of entering the Central Nervous System, and has antidepressant and anxiolytic effects.On July 31, 2008,... Solabegron Solabegron is a drug which acts as a selective agonist for the β3 adrenergic receptor. It is being developed for the treatment of overactive bladder and irritable bowel syndrome.,, It has been shown to produce visceral analgesia by releasing somatostatin from adipocytes. ,-Synthesis:K.H.... |
SR 59230A SR 59230A is a selective antagonist of the beta-3 adrenergic receptor, but subsequently shown to also act at α1 adrenoceptors at high doses. It has been shown to block the hyperthermia produced by MDMA in animal studies.... |
†There is no α1C receptor. At one time, there was a subtype known as C, but was found to be identical to one of the previously discovered subtypes. To avoid confusion, naming was continued with the letter D.
α receptors
α receptors have several functions in common, but also individual effects. Common (or still unspecified) effects include:- VasoconstrictionVasoconstrictionVasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
of arteries to heartHeartThe heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
(coronary artery). - Vasoconstriction of veins
- Decrease motility of smooth muscleSmooth muscleSmooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
in gastrointestinal tractGastrointestinal tractThe human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
α1 receptor
Alpha1-adrenergic receptors are members of the G protein-coupled receptor superfamily. Upon activation, a heterotrimeric G protein, Gq, activates phospholipase C (PLCPhospholipase C
Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in...
). The PLC cleaves phosphatidylinositol 4,5-bisphosphate
Phosphatidylinositol 4,5-bisphosphate
Phosphatidylinositol 4,5-bisphosphate or PtdInsP2, also known simply as PIP2, is a minor phospholipid component of cell membranes...
(PIP2), which in turn causes an increase in inositol triphosphate
Inositol triphosphate
Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell...
(IP3) and diacylglycerol (DAG). The former interacts with calcium channels of endoplasmic and sarcoplasmic reticulum, thus changing the calcium content in a cell. This triggers all other effects.
Specific actions of the α1 receptor mainly involve smooth muscle contraction. It causes vasoconstriction
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
in many blood vessels, including those of the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, gastrointestinal system, kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
(renal artery
Renal artery
The renal arteries normally arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle with the aorta....
) and brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. Other areas of smooth muscle contraction are:
- ureterUreterIn human anatomy, the ureters are muscular tubes that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually long and ~3-4 mm in diameter....
- vas deferensVas deferensThe vas deferens , also called ductus deferens, , is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation....
- hairHairHair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
(arrector pili muscles) - uterusUterusThe uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
(when pregnant) - urethral sphincterUrethral sphincterThe term urethral sphincter refers to one of two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are the external urethral sphincter and the internal urethral sphincter...
- bronchioles (although minor to the relaxing effect of β2 receptor on bronchioles)
- blood vessels of ciliary body (stimulation causes mydriasisMydriasisMydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
)
Further effects include glycogenolysis
Glycogenolysis
Glycogenolysis is the conversion of glycogen polymers to glucose monomers. Glycogen is catabolized by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate...
and gluconeogenesis
Gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....
from adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
and liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, as well as secretion from sweat gland
Sweat gland
Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...
s and Na+
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
reabsorption from kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
.
Antagonists may be used in hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
.
α2 receptor
There are 3 highly homologous subtypes of α2 receptors: α2A, α2Β, and α2C.Specific actions of the α2 receptor include:
- inhibition of insulinInsulinInsulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
release in the pancreasPancreasThe pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
. - induction of glucagonGlucagonGlucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...
release from the pancreas. - contraction of sphincterSphincterA sphincter is an anatomical structure, or a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning...
s of the gastrointestinal tractGastrointestinal tractThe human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. .... - negative feedback in the neuronal synapses - presynaptic inhibition of noradrenalin release in CNS
- increased thrombocyte aggregation
β1 receptor
Specific actions of the β1 receptor include:- Increase cardiac outputCardiac outputCardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
, by raising heart rate (positive chronotropic effect), increasing impulse conduction (positive dromotropic effect), and increasing contraction (positive inotropic effect), thus increasing the volume expelled with each beat (increased ejection fraction). - Increase reninReninRenin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
secretion from juxtaglomerular cellJuxtaglomerular cellThe juxtaglomerular cells are cells in the kidney that synthesize, store, and secrete the enzyme renin. They are specialized smooth muscle cells in the wall of the afferent arteriole that delivers blood to the glomerulus...
of kidney. - Increase ghrelinGhrelinGhrelin is a 28 amino acid peptide and hormone that is produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone...
secretion from the stomach
β2 receptor
Specific actions of the β2 receptor include the following:- Smooth muscleSmooth muscleSmooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
relaxation, e.g. in bronchi, GI tract (decreased motility). - LipolysisLipolysisLipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
in adipose tissueAdipose tissueIn histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
. - AnabolismAnabolismAnabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or as 'catabolic', which is the opposite...
in skeletal muscleSkeletal muscleSkeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
. - Relax non-pregnant uterusUterusThe uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
- Relax detrusor urinae muscle of bladderUrinary bladderThe urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
wall - Dilate arteries to skeletal muscleSkeletal muscleSkeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
- GlycogenolysisGlycogenolysisGlycogenolysis is the conversion of glycogen polymers to glucose monomers. Glycogen is catabolized by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate...
and gluconeogenesisGluconeogenesisGluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids.... - Stimulates insulinInsulinInsulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
secretion - Contract sphincters of GI tract
- Thickened secretions from salivary glandSalivary glandThe salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose...
s. - Inhibit histamineHistamineHistamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
-release from mast cells - Increase reninReninRenin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
secretion from kidneyKidneyThe kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and... - Relaxation of Bronchioles (salbutamolSalbutamolSalbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....
, a beta 2 agonist relieves bronchiole constriction) - Involved in brain - immune communication
β3 receptor
Specific actions of the β3 receptor include:- Enhancement of lipolysisLipolysisLipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
in adipose tissueAdipose tissueIn histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
. Beta-3 activating drugs could theoretically be used as weight-loss agents, but are limited by the side effect of tremors.
External links
- Alpha receptors illustrated
- The Adrenergic Receptors
- Basic Neurochemistry: α- and β-Adrenergic Receptors
- Brief overview of functions of the beta-3 receptor
- Theory of receptor activation
- Desensitization of beta-1-receptors - 3D structure of beta-2 adrenergic receptor in membrane