Alpha-2 blocker
Encyclopedia
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 sometimes used in veterinary medicine (although now largely replaced by atipamezole
) for reversing the effects of alpha-2 agonists such as medetomidine
which are used as sedatives during surgery.
One area where alpha-2 blockers are medically useful is in treating depression
; the tetracyclic antidepressants mianserin
and mirtazapine
are alpha-2 blockers, though their efficacy as antidepressants may come from their activity at other receptor sites.
Alpha-2 blockers increases significantly adrenergic, dopaminergic and serotonergic neurotransmitters, increases insulin secretion and decreases blood sugar levels.
Withdrawal from alpha2 blockers can be difficult or too dangerous as the global downregulation of neurotransmitters can cause symptoms of depression and other neurological problems and increased blood sugar levels together with decreased insulin sensitivity can cause diabetes. Reduced microcirculation
together with adrenaline supersensitivity in organs such as liver can also be difficult problem when withdrawing from adrenergic blockers.
, idazoxan
, yohimbine
, and rauwolscine
.
Alpha blocker
Alpha-1 blockers constitute a variety of drugs which block α1-adrenergic receptors in arteries and smooth muscles.-Pharmacology:...
generally refers to α1-blockers, there are also α2-blockers, which are antagonists
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
to the α2 adrenergic receptor
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...
. They are mainly used in research, finding little clinical application in human medicine, although 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...
was previously used as an 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...
, and is still sometimes used in veterinary medicine (although now largely replaced by 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:*...
) for reversing the effects of alpha-2 agonists such as medetomidine
Medetomidine
Medetomidine 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...
which are used as sedatives during surgery.
One area where alpha-2 blockers are medically useful is in treating depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
; the tetracyclic antidepressants 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...
and 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...
are alpha-2 blockers, though their efficacy as antidepressants may come from their activity at other receptor sites.
Alpha-2 blockers increases significantly adrenergic, dopaminergic and serotonergic neurotransmitters, increases insulin secretion and decreases blood sugar levels.
Withdrawal from alpha2 blockers can be difficult or too dangerous as the global downregulation of neurotransmitters can cause symptoms of depression and other neurological problems and increased blood sugar levels together with decreased insulin sensitivity can cause diabetes. Reduced microcirculation
Microcirculation
The microcirculation is a term used to describe the small vessels in the vasculature which are embedded within organs and are responsible for the distribution of blood within tissues; as opposed to larger vessels in the macrocirculation which transport blood to and from the organs...
together with adrenaline supersensitivity in organs such as liver can also be difficult problem when withdrawing from adrenergic blockers.
Examples
Examples include atipamezole, efaroxanEfaroxan
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...
, 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...
, and rauwolscine
Rauwolscine
Rauwolscine, 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...
.