Agonists •
4-NEMD •
7-Me-marsanidine (also
I1 agonist) •
Agmatine (also
I agonist,
NMDA,
5-HT3,
nicotinic antagonist and
NOS inhibitor) •
Apraclonidine •
Brimonidine •
Cannabigerol (also acts as a moderate affinity
5-HT1A receptor antagonist, and low affinity
CB1 receptor antagonist). •
Clonidine (also
I1 agonist) •
Detomidine •
Dexmedetomidine •
Fadolmidine •
Guanabenz •
Guanfacine •
Lofexidine •
Marsanidine •
Medetomidine •
Methyldopa •
Mivazerol •
Oxymetazoline (also
α1 agonist) •
Tiamenidine •
Tizanidine •
Tolonidine •
Xylazine •
Xylometazoline Norepinephrine has higher affinity for the α2 receptor than
epinephrine does, and therefore relates less to the latter's functions. clonidine also helps alleviate symptoms of
opioid withdrawal. 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. However, it is now known that clonidine binds to
imidazoline receptors with a much greater affinity than α2 receptors, which would account for its applications outside the field of hypertension alone. Imidazoline receptors occur in the
nucleus tractus solitarii and also the
centrolateral medulla. Clonidine is now thought to decrease blood pressure via this central mechanism. Other nonselective agonists include
dexmedetomidine,
lofexidine (another antihypertensive),
TDIQ (partial agonist),
tizanidine (in
spasms,
cramping) and
xylazine. Xylazine has
veterinary use. In the European Union, dexmedetomidine received a marketing authorization from the
European Medicines Agency (EMA) on August 10, 2012, under the brand name of
Dexdor. It is indicated for sedation in the
ICU for patients needing mechanical ventilation. 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. α2A selective agonists include
guanfacine (an antihypertensive) and brimonidine (UK 14,304).
(R)-3-nitrobiphenyline is an α2C selective agonist as well as being a weak
antagonist at the α and α subtypes.
Antagonists •
1-PP (active metabolite of
buspirone and
gepirone) •
Aripiprazole •
Asenapine •
Atipamezole •
Cirazoline •
Clozapine •
Efaroxan •
Fipamezole •
Idazoxan •
Lurasidone •
Melperone •
Mianserin •
Mirtazapine •
Napitane •
Olanzapine •
Paliperidone (also primary active metabolite of
risperidone) •
Phenoxybenzamine •
Phentolamine •
Piribedil •
Rauwolscine •
Risperidone •
Rotigotine (
α2B antagonist, non-selective) •
Quetiapine •
Norquetiapine (primary active metabolite of
quetiapine) •
Setiptiline •
Tolazoline •
Yohimbine •
Ziprasidone •
Zotepine (discontinued) Non-selective
α blockers include, A-80426,
atipamezole,
phenoxybenzamine,
efaroxan,
idazoxan and
SB-269,970.
Yohimbine is a relatively selective α2 blocker that has been investigated as a treatment for erectile dysfunction.
Tetracyclic antidepressants
mirtazapine and
mianserin are also potent α antagonists with mirtazapine being more selective for α2 subtype (~30-fold selective over α1) than mianserin (~17-fold). α2A selective blockers include
BRL-44408 and RX-821,002. α2B selective blockers include ARC-239 and
imiloxan. α2C selective blockers include JP-1302 and
spiroxatrine, the latter also being a
serotonin 5-HT1A antagonist. == See also ==