By Dr Ananya Mandal, MD
Histamine is an autacoid, which means it acts similarly to a local hormone, near its site of synthesis. It is produced as part of the local immune response to invading bodies and triggers inflammation.
It also acts as a neurotransmitter or chemical messenger that carries signals from one nerve to another, as well as performing several important functions in the bowel.
Histamine exerts its effects by acting on specific histamine receptors. These receptors were characterized in 1966. There are four basic types of histamine receptor that have been discovered and these are described below.
- The H1 histamine receptor is found on the smooth muscle, central nervous system tissue and the endothelium. The binding of histamine to this receptor causes blood vessel dilation, bronchoconstriction and contraction of smooth muscle. In addition, endothelial cells separate which causes hives and pain and itching occur. The H1 receptor is the main receptor involved in allergic rhinitis and also motion sickness.
- The H2 receptor is found on the parietal cells within the stomach. These cells normally help produce the gastric acids required for digestion. Stimulation of these receptors leads to acid production in the stomach.
- The H3 histamine receptor is found in the central nervous system and to a lesser degree in the tissue of the peripheral nervous system. The binding of histamine to this receptors leads to a decrease in the release of the neurotransmitters histamine acetylcholine, serotonin and norepinephrine.
- The H4 histamine receptor is mainly found in basophils and in bone marrow. It is also present in the small intestine, colon, spleen and thymus. Stimulation of this receptor plays a role in chemotaxis.
Reviewed by Sally Robertson, BSc
Last Updated: Aug 19, 2014