Alpha-2 adrenergic receptor
Encyclopedia
The alpha-2 adrenergic receptor (or adrenoceptor) 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. Catecholamine
s like norepinephrine
(noradrenaline) and epinephrine
(adrenaline) signal through the α2-adrenergic receptor in the central
and peripheral nervous system
s.
and epinephrine (adrenaline) released by the adrenal medulla
, binding epinephrine with slightly higher affinity. It has several general functions in common with the α1-adrenergic receptor
, but also has specific effects of its own.
- 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
, so proteins such as phosphorylase kinase
cannot be phosphorylated by PKA. In particular, phosphorylase kinase is responsible for the phosphorylation and activation of glycogen phosphorylase
, an enzyme necessary for glycogen breakdown. Thus in this pathway, the downstream effect of adenyl cyclase inactivation is decreased breakdown of glycogen.
The relaxation of gastrointestinal tract motility is by presynaptic inhibition, where transmitters inhibit further release by homotropic effects.
Antagonists
has higher affinity for the α-2 receptor than has epinephrine
. Nonselective agonists include the antihypertensive
drug clonidine
, used to lower blood pressure and hot flashes associated with menopausal symptoms. Clonidine has also been successfully used in indications that exceed what would be expected from a simple blood-pressure lowering drug: it has recently shown positive results in children with ADHD who suffer from tics resulting from the treatment with a CNS stimulant drug, such as Adderall XR or methylphenidate
; clonidine also helps alleviate symptoms of opioid withdrawal. The hypotensive effect of clonidine was initially attributed through its agonist action on presynaptic α-2 receptors, which act as a down-regulator on the amount of norepinephrine released in the synaptic cleft, an example of autoreceptor
. However, it is now known that clonidine binds to imidazoline receptor
s with a much greater affinity than α-2 receptors, which would account for its applications outside the field of hypertension alone. Imidazoline receptors occur in the Nucleus Tractus Solitarii
and also the Ventrolateral Medulla
. Clonidine is now thought to decrease BP via this central mechanism. Other nonselective agonists include dexmedetomidine
, lofexidine
(another antihypertensive), TDIQ
(partial agonist), tizanidine
(in spasms
, cramping), UK-14,304 and xylazine
. Xylazine has veterinary use; in non-human species this is an immobilizing and anesthetic drug, presumptively also mediated by α-2 adrenergic receptors because it is reversed by yohimbine, an α-2 antagonist.
α2A selective agonists include guanfacine
(an antihypertensive) and octopamine
, which is also a β3 agonist.
(R)-3-Nitrobiphenyline
is an α2C selective agonist.
s include, A-80426, atipamezole
, phenoxybenzamine
, efaroxan
, idazoxan
*(experimental), mirtazapine
(a tetracyclic antidepressant
), mianserin
(a tetracyclic antidepressant
), SB-269,970
and yohimbine
* (a purported aphrodisiac
).
α2A selective alpha blockers include BRL-44408
and RX-821,002, while α2B selective alpha blockers include ARC-239 and imiloxan
.
α2C selective alpha blockers include JP-1302 and spiroxatrine
, the latter also being a serotonin 5-HT1A antagonist.
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...
(GPCR) associated with the 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...
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. 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 like norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
(noradrenaline) and 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...
(adrenaline) signal through the α2-adrenergic receptor in the central
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
and peripheral nervous system
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
s.
Effects
The α2-adrenergic receptor binds both norepinephrine released by sympathetic postganglionic fibersSympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
and epinephrine (adrenaline) released by the adrenal medulla
Adrenal medulla
The adrenal medulla is part of the adrenal gland. It is located at the center of the gland, being surrounded by the adrenal cortex. It is the innermost part of the adrenal gland, consisting of cells that secrete epinephrine , norepinephrine , and a small amount of dopamine in response to...
, binding epinephrine with slightly higher affinity. It has several general functions in common with the α1-adrenergic receptor
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...
, but also has specific effects of its own.
General
Common (or still unspecified) effects include:- VasodilationVasodilationVasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
of arteries - Vasoconstriction 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) however the extent of this effect may be limited and may be negated by the vasodilatory effect from β₂ receptors - Constriction of some vascular smooth muscle
- 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. .... - Contraction of male genitalia during ejaculationEjaculationEjaculation is the ejecting of semen from the male reproductory tract, and is usually accompanied by orgasm. It is usually the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. In rare cases ejaculation occurs because of prostatic disease...
- Inhibition of lipolysis
Individual
Individual actions of the α2 receptor include:- Mediates synaptic transmission in pre- and postsynaptic nerve terminalsSynapseIn the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
- Decrease release of acetylcholineAcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
- Decrease release of norepinephrineNorepinephrineNorepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
- Inhibit norepinephrine system in brain
- Decrease release of acetylcholine
- Inhibition 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... - 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 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 pancreas - platelet aggregation
- 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. .... - ↓ Secretion 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...
- Relax gastrointestinal tractGastrointestinal tractThe human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
(presynaptic effect) - Decreased aqueous humor fluid production from the ciliary body
Signaling cascade
The alpha subunit of an inhibitory G proteinG protein
G 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...
- 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...
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
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...
produced from ATP. This leads to a decrease of intracellular cAMP. Protein Kinase A is not able to be activated by cAMP
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...
, so proteins such as phosphorylase kinase
Phosphorylase kinase
Phosphorylase kinase is a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen...
cannot be phosphorylated by PKA. In particular, phosphorylase kinase is responsible for the phosphorylation and activation of glycogen phosphorylase
Glycogen phosphorylase
Glycogen phosphorylase is one of the phosphorylase enzymes . Glycogen phosphorylase catalyzes the rate-limiting step in the degradation of glycogen in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond...
, an enzyme necessary for glycogen breakdown. Thus in this pathway, the downstream effect of adenyl cyclase inactivation is decreased breakdown of glycogen.
The relaxation of gastrointestinal tract motility is by presynaptic inhibition, where transmitters inhibit further release by homotropic effects.
Ligands
Agonists- ApraclonidineApraclonidineApraclonidine , also known as Iopidine, is a sympathomimetic used in glaucoma therapy. It is an α2-adrenergic agonist and a weak alpha-1 adrenergic receptor agonist....
- BrimonidineBrimonidineBrimonidine is a drug used to treat open-angle glaucoma or ocular hypertension.It acts via decreasing synthesis of aqueous humor, and increasing the amount that drains from the eye through uveoscleral outflow.As a treatment for glaucoma, it is usually given in eyedrop form.Brimonidine is an...
- ClonidineClonidineClonidine is a sympatholytic medication used to treat medical conditions, such as high blood pressure, some pain conditions, ADHD and anxiety/panic disorder...
- DetomidineDetomidineDetomidine is an imidazole derivative and α2-adrenergic agonist, used as a large animal sedative, primarily used in horses. It is usually available as the salt detomidine hydrochloride...
- DexmedetomidineDexmedetomidineDexmedetomidine is a sedative medication used by intensive care units and anesthetists. It is relatively unique in its ability to provide sedation without causing respiratory depression...
- GuanabenzGuanabenzGuanabenz is an alpha agonist of the alpha-2 type that is used as an antihypertensive drug. It is used to treat high blood pressure ....
- GuanfacineGuanfacineGuanfacine is a sympatholytic. It is an agonist of the α2A subtype of norepinephrine receptors. These receptors are concentrated heavily in the prefrontal cortex and the locus coeruleus, with the potential to improve attention abilities via modulating post-synaptic α2A receptors in the prefrontal...
- LofexidineLofexidineLofexidine is an alpha2-adrenergic receptor agonist, historically used as a short-acting anti-hypertensive, but more commonly used to alleviate physical symptoms of heroin and opiate withdrawal.-Indication:...
- MedetomidineMedetomidineMedetomidine is a synthetic drug used as both a surgical anesthetic and analgesic often used as the hydrochloride salt medetomidine hydrochloride. It is a crystalline white alpha-two adrenergic agonist that can be administered as an intravenous drug solution with sterile water...
- RomifidineRomifidineRomifidine is a drug that is used in veterinary medicine as a sedative mainly in large animals such as horses, although it may be used in a wide variety of species. It is not used in humans, but is closely related in structure to the commonly used drug clonidine.Romifidine acts as an agonist at the...
- TizanidineTizanidineTizanidine is a drug that is used as a muscle relaxant. It is a centrally acting α2 adrenergic agonist. It is used to treat the spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, spastic diplegia, back pain, or certain other injuries to the spine or...
- TolonidineTolonidineTolonidine is an antihypertensive....
- XylazineXylazineXylazine is a drug that is used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle and other non-human mammals. An analogue of clonidine, it is an agonist at the α2 class of adrenergic receptor....
- Fadolmidine
- XylometazolineXylometazolineXylometazoline is a drug which is used as a topical nasal decongestant. It is applied directly into the nose, either as a spray or as drops....
- OxymetazolineOxymetazolineOxymetazoline is a selective alpha-1 agonist and partial alpha-2 agonist topical decongestant, used in the form of Oxymetazoline hydrochloride, in products such as Afrin, Dristan, Nasivin, Logicin, Vicks Sinex, Visine L.R., Sudafed OM, and Zicam. It was developed from Xylometazoline at E.Merck...
Antagonists
- AtipamezoleAtipamezoleAtipamezole 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:*...
- CirazolineCirazolineCirazoline is a nonselective agonist of the alpha-1 adrenergic receptor , and an antagonist to the alpha-2 adrenergic receptor. It is believed that this combination of properties could make cirazoline an effective vasoconstricting agent....
- EfaroxanEfaroxanEfaroxan is an α2-adrenergic receptor antagonist....
- IdazoxanIdazoxanIdazoxan 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...
- MianserinMianserinMianserin is a psychoactive drug of the tetracyclic antidepressant chemical class which is classified as a noradrenergic and specific serotonergic antidepressant and has antidepressant, anxiolytic, hypnotic, antiemetic, orexigenic, and antihistamine effects...
- MirtazapineMirtazapineMirtazapine is a tetracyclic antidepressant used primarily in the treatment of depression. It is also sometimes used as a hypnotic, antiemetic, and appetite stimulant, and for the treatment of anxiety, among other indications...
- Napitane
- PhenoxybenzaminePhenoxybenzaminePhenoxybenzamine is a non-selective, irreversible alpha antagonist.-Uses:It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma...
- PhentolaminePhentolaminePhentolamine is a reversible nonselective alpha-adrenergic antagonist. -Mechanism:Its primary action is vasodilation due to α1 blockade....
- RauwolscineRauwolscineRauwolscine, also known as isoyohimbine, α-yohimbine, and corynanthidine, is an alkaloid found in various species within the genera Rauwolfia and Pausinystalia . It is a stereoisomer of yohimbine...
- SetiptilineSetiptilineSetiptiline , also known as teciptiline, is a tetracyclic antidepressant which acts as a noradrenergic and specific serotonergic antidepressant...
- TolazolineTolazolineTolazoline is a non-selective competitive α-adrenergic receptor antagonist. It is a vasodilator that is used to treat spasms of peripheral blood vessels...
- YohimbineYohimbineYohimbine 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...
Agonists
NorepinephrineNorepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
has higher affinity for the α-2 receptor than has 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...
. Nonselective agonists include the antihypertensive
Antihypertensive
The antihypertensives are a class of drugs that are used to treat hypertension . Evidence suggests that reduction of the blood pressure by 5 mmHg can decrease the risk of stroke by 34%, of ischaemic heart disease by 21%, and reduce the likelihood of dementia, heart failure, and mortality from...
drug clonidine
Clonidine
Clonidine is a sympatholytic medication used to treat medical conditions, such as high blood pressure, some pain conditions, ADHD and anxiety/panic disorder...
, used to lower blood pressure and hot flashes associated with menopausal symptoms. Clonidine has also been successfully used in indications that exceed what would be expected from a simple blood-pressure lowering drug: it has recently shown positive results in children with ADHD who suffer from tics resulting from the treatment with a CNS stimulant drug, such as Adderall XR or methylphenidate
Methylphenidate
Methylphenidate is a psychostimulant drug approved for treatment of attention-deficit hyperactivity disorder, postural orthostatic tachycardia syndrome and narcolepsy. It may also be prescribed for off-label use in treatment-resistant cases of lethargy, depression, neural insult and obesity...
; clonidine also helps alleviate symptoms of opioid withdrawal. The hypotensive effect of clonidine was initially attributed through its agonist action on presynaptic α-2 receptors, which act as a down-regulator on the amount of norepinephrine released in the synaptic cleft, an example of autoreceptor
Autoreceptor
An autoreceptor is a receptor located on presynaptic nerve cell membranes and serves as a part of a feedback loop in signal transduction. It is sensitive only to those neurotransmitters or hormones that are released by the neuron in whose membrane the autoreceptor sits.Canonically, a presynaptic...
. However, it is now known that clonidine binds to imidazoline receptor
Imidazoline receptor
Imidazoline receptors are receptors for clonidine and other imidazolines.-Classes:There are three classes of imidazoline receptors:* I1 receptor – mediates the sympatho-inhibitory actions of imidazolines to lower blood pressure, * I2 receptor – an allosteric binding site of monoamine oxidase and is...
s with a much greater affinity than α-2 receptors, which would account for its applications outside the field of hypertension alone. Imidazoline receptors occur in the Nucleus Tractus Solitarii
Solitary nucleus
The solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...
and also the Ventrolateral Medulla
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
. Clonidine is now thought to decrease BP via this central mechanism. Other nonselective agonists include dexmedetomidine
Dexmedetomidine
Dexmedetomidine is a sedative medication used by intensive care units and anesthetists. It is relatively unique in its ability to provide sedation without causing respiratory depression...
, lofexidine
Lofexidine
Lofexidine is an alpha2-adrenergic receptor agonist, historically used as a short-acting anti-hypertensive, but more commonly used to alleviate physical symptoms of heroin and opiate withdrawal.-Indication:...
(another antihypertensive), TDIQ
TDIQ
TDIQ is a drug used in scientific research, which has anxiolytic and anorectic effects in animals...
(partial agonist), tizanidine
Tizanidine
Tizanidine is a drug that is used as a muscle relaxant. It is a centrally acting α2 adrenergic agonist. It is used to treat the spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, spastic diplegia, back pain, or certain other injuries to the spine or...
(in spasms
Spasms
-Plot:Jason Kincaid has this massive serpent captured and brought to the US because it killed his brother and he now shares some kind of psychic link with it...
, cramping), UK-14,304 and xylazine
Xylazine
Xylazine is a drug that is used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle and other non-human mammals. An analogue of clonidine, it is an agonist at the α2 class of adrenergic receptor....
. Xylazine has veterinary use; in non-human species this is an immobilizing and anesthetic drug, presumptively also mediated by α-2 adrenergic receptors because it is reversed by yohimbine, an α-2 antagonist.
α2A selective agonists include guanfacine
Guanfacine
Guanfacine is a sympatholytic. It is an agonist of the α2A subtype of norepinephrine receptors. These receptors are concentrated heavily in the prefrontal cortex and the locus coeruleus, with the potential to improve attention abilities via modulating post-synaptic α2A receptors in the prefrontal...
(an antihypertensive) and octopamine
Octopamine
Octopamine is an endogenous biogenic amine that is closely related to norepinephrine, and has effects on the adrenergic and dopaminergic systems. It is also found naturally in numerous plants, including bitter orange. Biosynthesis of the D--enantiomer of octopamine is by β-hydroxylation of...
, which is also a β3 agonist.
(R)-3-Nitrobiphenyline
(R)-3-Nitrobiphenyline
-3-Nitrobiphenyline is a drug which acts as an α2-adrenergic agonist, selective for the α2C subtype, as well as being a weak antagonist at the α2A and α2B subtypes....
is an α2C selective agonist.
Antagonists
Nonselective alpha blockerAlpha blocker
Alpha-1 blockers constitute a variety of drugs which block α1-adrenergic receptors in arteries and smooth muscles.-Pharmacology:...
s include, A-80426, atipamezole
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:*...
, phenoxybenzamine
Phenoxybenzamine
Phenoxybenzamine is a non-selective, irreversible alpha antagonist.-Uses:It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma...
, efaroxan
Efaroxan
Efaroxan is an α2-adrenergic receptor antagonist....
, idazoxan
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...
*(experimental), mirtazapine
Mirtazapine
Mirtazapine is a tetracyclic antidepressant used primarily in the treatment of depression. It is also sometimes used as a hypnotic, antiemetic, and appetite stimulant, and for the treatment of anxiety, among other indications...
(a tetracyclic antidepressant
Tetracyclic antidepressant
Tetracyclic antidepressants are a class of drugs used primarily as antidepressants that were first introduced in the 1970s. They are named after their chemical structure which contains four rings of atoms and are closely related to the tricyclic antidepressants which contain three rings of...
), mianserin
Mianserin
Mianserin is a psychoactive drug of the tetracyclic antidepressant chemical class which is classified as a noradrenergic and specific serotonergic antidepressant and has antidepressant, anxiolytic, hypnotic, antiemetic, orexigenic, and antihistamine effects...
(a tetracyclic antidepressant
Tetracyclic antidepressant
Tetracyclic antidepressants are a class of drugs used primarily as antidepressants that were first introduced in the 1970s. They are named after their chemical structure which contains four rings of atoms and are closely related to the tricyclic antidepressants which contain three rings of...
), SB-269,970
SB-269,970
SB-269,970 is a drug and research chemical developed by GlaxoSmithKline used in scientific studies. It was previously believed to act as a selective 5-HT7 receptor antagonist , but a subsequent discovery showed that it also potently blocks the α2-adrenergic receptor...
and yohimbine
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...
* (a purported aphrodisiac
Aphrodisiac
An aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...
).
α2A selective alpha blockers include BRL-44408
BRL-44408
BRL-44408 is a drug used in scientific research which acts as a selective antagonist for the α2A adrenoreceptor. It has been suggested as having potential therapeutic application in the treatment of extrapyramidal side effects produced by some antipsychotic medications....
and RX-821,002, while α2B selective alpha blockers include ARC-239 and imiloxan
Imiloxan
Imiloxan is a drug which is used in scientific research. It acts as a selective antagonist for the α2B adrenergic receptor, and has been useful for distinguishing the actions of the different α2 adrenergic subtypes.-Chemistry:...
.
α2C selective alpha blockers include JP-1302 and spiroxatrine
Spiroxatrine
Spiroxatrine is drug which acts as a selective antagonist at both the 5-HT1A receptor and the α2C adrenergic receptor. It is an analogue of spiperone, and also has some dopamine antagonist effects....
, the latter also being a serotonin 5-HT1A antagonist.