Histamine H4 receptor

The histamine H4 receptor is, like the other three histamine receptors, a member of the G protein-coupled receptor superfamily.

Location
H4 is highly expressed in bone marrow and white blood cells and regulates zymosan-induced neutrophil release from bone marrow and subsequent infiltration in the pleurisy model along with L-selectin. It is also expressed in the colon, liver, lung, small intestine, spleen, testes, thymus, tonsils, and trachea.

Functions
They have been shown to mediate mast cell chemotaxis. It seems to do this by the mechanism of Gi-coupled decrease in cAMP.

Pharmacologic potential
By inhibiting the H4 receptor, asthma and allergy may be treated.

High affinity substances
The following substances have been found to bind with high affinity to this receptor:
 * amitriptyline
 * chlorpromazine
 * doxepin
 * promethazine
 * cinnarizine

Moderate affinity substances
The following substances have been found to bind with moderate affinity to this receptor:
 * cyproheptadine
 * clemizole
 * mianserin
 * clozapine
 * chlorpheniramine
 * histamine

Weak affinity substances
The following substances have been found to bind with weak affinity to this receptor:
 * imetit
 * pheniramine
 * dimaprit