Imidazoline receptors are receptor

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

s for clonidine

Clonidine

Clonidine is a sympatholytic medication used to treat medical conditions, such as high blood pressure, some pain conditions, ADHD and anxiety/panic disorder...

 and other imidazoline

Imidazoline

Imidazoline is a nitrogen-containing heterocycle with formula C3H6N2, derived from imidazole. The ring contains an imine bond, and the carbons at the 4 and 5 positions are singly bonded, rather than doubly bonded for the case of imidazole...

s.

Classes

There are three classes of imidazoline receptors:

• I₁ receptor – mediates the sympatho-inhibitory actions of imidazolines to lower blood pressure, (NISCH
  NISCH
  Nischarin is a protein that in humans is encoded by the NISCH gene.-Further reading:...
  
   or IRAS, imidazoline receptor antisera selected)
• I₂ receptor – an allosteric
  Allosteric regulation
  In biochemistry, allosteric regulation is the regulation of an enzyme or other protein by binding an effector molecule at the protein's allosteric site . Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are...
  
   binding site of monoamine oxidase
  Monoamine oxidase
  L-Monoamine oxidases are a family of enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. The enzyme was originally discovered by Mary Bernheim in the liver and was named tyramine oxidase...
  
   and is involved in pain modulation and neuroprotection.
• I₃ receptor – regulates insulin
  Insulin
  Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
  
   secretion from pancreatic beta cell
  Beta cell
  Beta cells are a type of cell in the pancreas located in the so-called islets of Langerhans. They make up 65-80% of the cells in the islets.-Function:...
  
  s

Activated I₁-imidazoline receptors trigger the hydrolysis of phosphatidylcholine

Phosphatidylcholine

Phosphatidylcholines are a class of phospholipids that incorporate choline as a headgroup.They are a major component of biological membranes and can be easily obtained from a variety of readily available sources such as egg yolk or soy beans from which they are mechanically extracted or chemically...

 into DAG. Elevated DAG levels in turn trigger the synthesis of second messenger

Second messenger system

Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus. They relay the signals of hormones like epinephrine , growth factors, and others, and cause some kind of change in the activity of the cell...

s arachidonic acid

Arachidonic acid

Arachidonic acid is a polyunsaturated omega-6 fatty acid 20:4.It is the counterpart to the saturated arachidic acid found in peanut oil, Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6).It is the counterpart to the saturated arachidic acid found in peanut oil,...

 and downstream eicosanoids. In addition, the sodium-hydrogen antiporter

Sodium-hydrogen antiporter

The sodium–hydrogen antiporter or sodium–hydrogen exchanger is a membrane protein found in many cells, and especially in those of the nephron of the kidney...

 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 interleukin

Interleukin

Interleukins are a group of cytokines that were first seen to be expressed by white blood cells . The term interleukin derives from "as a means of communication", and "deriving from the fact that many of these proteins are produced by leukocytes and act on leukocytes"...

s.

Agonists

• Agmatine
  Agmatine
  Agmatine is the decarboxylation product of the amino acid arginine and is an intermediate in polyamine biosynthesis. It is discussed as a putative neurotransmitter. It is synthesized in the brain, stored in synaptic vesicles, accumulated by uptake, released by membrane depolarization, and...
  
   (endogenous agonist, non-selective, also binds to NMDA, nicotinic, and α₂ adrenoceptors)
• Apraclonidine
  Apraclonidine
  Apraclonidine , also known as Iopidine, is a sympathomimetic used in glaucoma therapy. It is an α2-adrenergic agonist and a weak alpha-1 adrenergic receptor agonist....
  
   (I₁ selective)
• Moxonidine
  Moxonidine
  Moxonidine is a new generation centrally acting antihypertensive drug licensed for the treatment of mild to moderate essential hypertension. It may have a role when thiazides, beta-blockers, ACE inhibitors and calcium channel blockers are not appropriate or have failed to control blood pressure...
  
  
• S-23515
• S-23757
• LNP-509
• 2-BFI (selective I₂ receptor agonist)
• BU224 (selective I₂ receptor agonist, low efficacy)
• LNP-911

Antagonists

• Idazoxan (non-selective, binds to I₂ receptor and α₂ adrenoceptor)
• BU99006 (alkylating agent, inactivates I₂ receptors)

Imidazoline I₂ receptor antagonists reversibly block NMDA receptor

NMDA receptor

The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....

-mediated Ca²⁺ influx and thus may inhibit excitotoxicity

Excitotoxicity

Excitotoxicity is the pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate such as the NMDA receptor and AMPA receptor are...

.