Alpha-2 adrenergic receptor

[1] Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α2-adrenergic receptor in the central and peripheral nervous systems.

[3] It is also located on the vascular smooth muscle cells of certain blood vessels, such as those found in skin arterioles or on veins, where it sits alongside the more plentiful α1-adrenergic receptor.

Agonists (activators) of the α2-adrenergic receptor are frequently used in anaesthesia where they affect sedation, muscle relaxation and analgesia through effects on the central nervous system (CNS).

[16] Nonselective α2 agonists include the antihypertensive drug clonidine,[16] which can be used to lower blood pressure and to reduce hot flashes associated with menopause.

Clonidine has also been successfully used in indications that exceed what would be expected from a simple blood-pressure lowering drug: it has shown positive results in children with ADHD who have tics resulting from the treatment with a CNS stimulant drug, such as Adderall XR or methylphenidate;[25] clonidine also helps alleviate symptoms of opioid withdrawal.

[26] The hypotensive effect of clonidine was initially attributed through its agonist action on presynaptic α2 receptors, which act as a down-regulator on the amount of norepinephrine released in the synaptic cleft, an example of autoreceptor.

In non-human species this is an immobilizing and anesthetic drug, presumptively also mediated by α2 adrenergic receptors because it is reversed by yohimbine, an α2 antagonist.