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, (NISCH or IRAS, imidazoline receptor antisera selected)
 * I2 receptor – an allosteric binding site of monoamine oxidase and is involved in pain modulation and neuroprotection.
 * I3 receptor – regulates insulin secretion from pancreatic beta cells

Activated I1-imidazoline receptors trigger the hydrolysis of phosphatidylcholine into DAG. Elevated DAG levels in turn trigger the synthesis of second messengers arachidonic acid and downstream eicosanoids. In addition, the sodium-hydrogen antiporter is inhibited, and enzymes of catecholamine synthesis is induced. The I1-imidazoline receptor may belong to the neurocytokine receptor family, since its signaling pathways are similar to those of interleukins.

Agonists

 * Agmatine (endogenous agonist, non-selective, also binds to NMDA, nicotinic, and α2 adrenoceptors)
 * Apraclonidine (I1 selective)
 * Moxonidine
 * S-23515
 * S-23757
 * LNP-509
 * 2-BFI (selective I2 receptor agonist)
 * BU224 (selective I2 receptor agonist, low efficacy)
 * LNP-911

Antagonists
Imidazoline I2 receptor antagonists reversibly block NMDA receptor-mediated Ca2+ influx and thus may inhibit excitotoxicity.
 * Idazoxan (non-selective, binds to I2 receptor and α2 adrenoceptor)
 * BU99006 (alkylating agent, inactivates I2 receptors)