Alpha-2 blockers (or α₂ blockers) are a subset of the alpha blocker class of drugs and are antagonists to the α₂ adrenergic receptor. They are mainly used in research, having found limited clinical application in human medicine. Alpha-2 blockers increase

noradrenaline Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...

release.

Uses

Yohimbine Yohimbine (), also known as quebrachine, is an indole alkaloid derived from the bark of the African tree '' Pausinystalia johimbe''; also from the bark of the unrelated South American tree ''Aspidosperma quebracho-blanco''. Yohimbine is an α2 ...

, historically used as an

aphrodisiac An aphrodisiac is a substance that increases sexual desire, sexual attraction, sexual pleasure, or sexual behavior. Substances range from a variety of plants, spices, foods, and synthetic chemicals. Natural aphrodisiacs like cannabis or cocai ...

, is sometimes used in veterinary medicine (although now largely replaced by

atipamezole Atipamezole (brand name Antisedan, also available in generic forms as Revertidine, is a synthetic α2 adrenergic receptor antagonist indicated for the reversal of the sedative and analgesic effects of dexmedetomidine and medetomidine in dogs. ...

) for reversing the effects of α₂s such as

medetomidine Medetomidine is a synthetic drug used as both a surgical anesthetic and analgesic. It is often used as the hydrochloride salt, medetomidine hydrochloride, a crystalline white solid. It is an α2 adrenergic agonist that can be administered as a ...

that are used as sedatives during surgery. The

tetracyclic antidepressant Tetracyclic antidepressants (TeCAs) are a class of antidepressants that were first introduced in the 1970s. They are named after their tetracyclic chemical structure, containing four rings of atoms, and are closely related to the tricyclic ant ...

s mianserin and mirtazapine are α₂ blockers, although their efficacy as antidepressants may come from their activity at other receptor sites. Mechanistically, α₂ blockers increase

adrenergic Adrenergic means "working on adrenaline (epinephrine) or noradrenaline (norepinephrine)" (or on their receptors). When not further qualified, it is usually used in the sense of enhancing or mimicking the effects of epinephrine and norepinephrine ...

, dopaminergic and

serotonergic Serotonergic () or serotoninergic () means "pertaining to or affecting serotonin". Serotonin is a neurotransmitter. A synapse is serotonergic if it uses serotonin as its neurotransmitter. A serotonergic neuron ''produces'' serotonin. A substance is ...

neurotransmitters and induce insulin secretion, decreasing blood sugar levels. Withdrawal from α₂ blockers can be difficult or dangerous as the global downregulation of neurotransmitters may cause symptoms of depression and other neurological problems, and increased blood sugar levels together with decreased insulin sensitivity can cause diabetes. Moreover, reduced

microcirculation The microcirculation is the circulation of the blood in the smallest blood vessels, the microvessels of the microvasculature present within organ tissues. The microvessels include terminal arterioles, metarterioles, capillaries, and venules. ...

together with adrenaline supersensitivity in organs such as liver can occur.

Examples

Examples include

efaroxan Efaroxan is an α2-adrenergic receptor antagonist and antagonist of the imidazoline receptor. Synthesis The Darzens reaction between 2-fluorobenzaldehyde 7848-46-1(1) and Ethyl 2-bromobutyrate 33-68-6(2) gives ethyl 2-ethyl-3-(2-fluorophenyl ...

idazoxan Idazoxan ( INN) 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 d ...

yohimbine Yohimbine (), also known as quebrachine, is an indole alkaloid derived from the bark of the African tree '' Pausinystalia johimbe''; also from the bark of the unrelated South American tree ''Aspidosperma quebracho-blanco''. Yohimbine is an α2 ...

, and

rauwolscine Rauwolscine, also known as isoyohimbine, α-yohimbine, and corynanthidine, is an alkaloid found in various species within the genera ''Rauvolfia'' and ''Corynanthe'' (including ''Pausinystalia''). It is a stereoisomer of yohimbine. Rauwolscine is ...

phentolamine Phentolamine, sold under the brand name Regitine among others, is a reversible nonselective α- adrenergic antagonist. Mechanism Its primary action is vasodilation due to α1 blockade. Non-selective α-blockers can cause a much more pronounced ...

References

External links

* {{antihypertensive-stub