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Histamine

Names
IUPAC name 2-(1H-imidazol-4-yl)ethanamine
Identifiers
CAS Number	51-45-6
3D model (JSmol)	Interactive image
ChEBI	CHEBI:18295
ChEMBL	ChEMBL90
ChemSpider	753
ECHA InfoCard	100.000.092
IUPHAR/BPS	1204
KEGG	D08040
MeSH	Histamine
PubChem CID	774
UNII	820484N8I3
CompTox Dashboard (EPA)	DTXSID4023125
InChI InChI=1S/C5H9N3/c6-2-1-5-3-7-4-8-5/h3-4H,1-2,6H2,(H,7,8)Key: NTYJJOPFIAHURM-UHFFFAOYSA-N InChI=1/C5H9N3/c6-2-1-5-3-7-4-8-5/h3-4H,1-2,6H2,(H,7,8)Key: NTYJJOPFIAHURM-UHFFFAOYAP
SMILES n1cc(nc1)CCN
Properties
Chemical formula	C5H9N3
Molar mass	111.145
Melting point	83.5 °C (182.3 °F)
Boiling point	209.5 °C (409.1 °F)
Solubility in water	Easily soluble in cold water, hot water
Solubility	Easily soluble in methanol. Very slightly soluble in diethyl ether. Easily soluble in ethanol.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.

Properties

Histamine forms colorless hygroscopic crystals that melt at 84°C, and are easily dissolved in water or ethanol, but not in ether. In aqueous solution histamine exists in two tautomeric forms, N-H-histamine and N-H-histamine.

Histamine has two basic centres, namely the aliphatic amino group and whichever nitrogen atom of the imidazole ring does not already have a proton. Under physiological conditions, the aliphatic amino group (having a pK_a around 9.4) will be protonated, whereas the second nitrogen of the imidazole ring (pK_a ≈ 5.8) will not be protonated. Thus, histamine is normally protonated to a singly charged cation.

Synthesis and metabolism

Histamine is derived from the decarboxylation of the amino acid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase. It is a hydrophilic vasoactive amine.

Once formed, histamine is either stored or rapidly inactivated by its primary degradative enzymes, histamine-N-methyltransferase or diamine oxidase. In the central nervous system, histamine released into the synapses is primarily broken down by histamine-N-methyltransferase, while in other tissues both enzymes may play a role. Several other enzymes, including MAO-B and ALDH2, further process the immediate metabolites of histamine for excretion or recycling.

Bacteria also are capable of producing histamine using histidine decarboxylase enzymes unrelated to those found in animals. A non-infectious form of foodborne disease, scombroid poisoning, is due to histamine production by bacteria in spoiled food, particularly fish. Fermented foods and beverages naturally contain small quantities of histamine due to a similar conversion performed by fermenting bacteria or yeasts. Sake contains histamine in the 20–40 mg/L range; wines contain it in the 2–10 mg/L range.

Storage and release

Most histamine in the body is generated in granules in mast cells or in white blood cells called basophils. Mast cells are especially numerous at sites of potential injury - the nose, mouth, and feet, internal body surfaces, and blood vessels. Non-mast cell histamine is found in several tissues, including the brain, where it functions as a neurotransmitter. Another important site of histamine storage and release is the enterochromaffin-like (ECL) cell of the stomach.

The most important pathophysiologic mechanism of mast cell and basophil histamine release is immunologic. These cells, if sensitized by IgE antibodies attached to their membranes, degranulate when exposed to the appropriate antigen. Certain amines and alkaloids, including such drugs as morphine, and curare alkaloids, can displace histamine in granules and cause its release. Antibiotics like polymyxin are also found to stimulate histamine release.

Histamine release occurs when allergens bind to mast-cell-bound 1gE antibodies. Reduction of 1gE overproduction may lower the likelihood of allergens finding sufficent free 1gH to trigger a mast-cell-release of histimine.

Mechanism of action

Histamine exerts its actions by combining with specific cellular histamine receptors. The four histamine receptors that have been discovered in humans are designated H1 through H4, and are all G protein-coupled receptors (GPCR). Histamine receptors in insects, like Drosophila melanogaster, are histamine-gated chloride channels that function in inhibition of neurons. Histamine-gated chloride channels are implicated in neurotransmission of peripheral sensory information in insects, especially in photoreception/vision. Two receptors subtypes have been identified in Drosophila, HClA and HClB. There are no known GPCRs for histamine in insects.

Effects on nasal mucous membrane

Increased vascular permeability causes fluid to escape from capillaries into the tissues, which leads to the classic symptoms of an allergic reaction: a runny nose and watery eyes. Allergens can bind to IgE-loaded mast cells in the nasal cavity's mucous membranes. This can lead to three clinical responses:

• sneezing due to histamine-associated sensory neural stimulation;

• hyper-secretion from glandular tissue; and

• nasal congestion due to vascular engorgement associated with vasodilation and increased capillary permeability.

Roles in the body

Sleep regulation

Histamine is released as a neurotransmitter. The cell bodies of histaminergics, the neurons which release histamine, are found in the posterior hypothalamus, in various tuberomammillary nuclei. From here, these neurons project throughout the brain, to the cortex through the medial forebrain bundle. Histaminergic action is known to modulate sleep. Classically, antihistamines (H1 histamine receptor antagonists) produce sleep. Likewise, destruction of histamine releasing neurons, or inhibition of histamine synthesis leads to an inability to maintain vigilance. Finally, H3 receptor antagonists increase wakefulness.

It has been shown that histaminergic cells have the most wakefulness-related firing pattern of any neuronal type thus far recorded. They fire rapidly during waking, fire more slowly during periods of relaxation/tiredness and completely stop firing during REM and NREM (non-REM) sleep. Histaminergic cells can be recorded firing just before an animal shows signs of waking.

Suppressive effects

While histamine has stimulatory effects upon neurons, it also has suppressive ones that protect against the susceptibility to convulsion, drug sensitization, denervation supersensitivity, ischemic lesions and stress. It has also been suggested that histamine controls the mechanisms by which memories and learning are forgotten.

Erection and sexual function

Libido loss and erectile failure can occur following histamine (H2) antagonists such as cimetidine and ranitidine. The injection of histamine into the corpus cavernosum in men with psychogenic impotence produces full or partial erections in 74% of them. It has been suggested that H2 antagonists may cause sexual difficulties by reducing the uptake of testosterone.

Schizophrenia

Metabolites of histamine are increased in the cerebrospinal fluid of people with schizophrenia, while the efficiency of H(1) receptor binding sites is decreased. Many atypical antipsychotic medications have the effect of increasing histamine turnover.

Disorders

As an integral part of the immune system, histamine may be involved in immune system disorders and allergies.

Nomenclature

"H substance" or "substance H" are occasionally used in medical literature for histamine or a hypothetical histamine-like diffusible substance released in allergic reactions of skin and in the responses of tissue to inflammation.

See also

• Scombroid food poisoning
• Histamine antagonist

References

1. ^ http://www.sciencelab.com/msds.php?msdsId=9924264
2. Marieb, E. (2001). Human anatomy & physiology. San Francisco: Benjamin Cummings. p. 414. ISBN 0-8053-4989-8.
3. Di Giuseppe, M.; et al. (2003). Nelson Biology 12. Toronto: Thomson Canada Ltd. p. 473. ISBN 0-17-625987-2. {{cite book}}: Explicit use of et al. in: |author= (help)
4. Paiva, T. B.; Tominaga, M.; Paiva, A. C. M. (1970). "Ionization of histamine, N-acetylhistamine, and their iodinated derivatives". Journal of Medicinal Chemistry. 13 (4): 689–692. doi:10.1021/jm00298a025. PMID 5452432.
5. http://astrobiology.berkeley.edu/PDFs_articles/WineAnalysisAnalChem.pdf
6. Hardie RC 1989 A histamine-activated chloride channel involved in neurotransmission at a photoreceptor synapse. Nature
7. Pantazis et al. 2008 Distinct Roles for Two Histamine Receptors (hclA and hclB) at the Drosophila Photoreceptor Synapse. Journal of Neuroscience
8. Monroe, E., Daly, A., and Shalhoub, R. 1997. "Appraisal of the validity of histamine-induced wheal and flare to predict the clinical efficacy of antihistamines". Journal of Allergy and Clinical Immunology 99(2): S789-806.
9. Yanai, K; Tashiro, M (2007). "The physiological and pathophysiological roles of neuronal histamine: an insight from human positron emission tomography studies". Pharmacology & therapeutics. 113 (1): 1–15. doi:10.1016/j.pharmthera.2006.06.008. PMID 16890992.
10. Alvarez, EO (2009). "The role of histamine on cognition". Behavioural brain research. 199 (2): 183–9. doi:10.1016/j.bbr.2008.12.010. PMID 19126417.
11. ^ White, JM; Rumbold, GR (1988). "Behavioural effects of histamine and its antagonists: a review". Psychopharmacology. 95 (1): 1–14. PMID 3133686.
12. Cará, AM; Lopes-Martins, RA; Antunes, E; Nahoum, CR; De Nucci, G (1995). "The role of histamine in human penile erection". British journal of urology. 75 (2): 220–4. PMID 7850330.
13. Ito, C (2004). "The role of the central histaminergic system on schizophrenia". Drug news & perspectives. 17 (6): 383–7. PMID 15334189.

External links

• DrugBank EXPT01785

• Histamine and Histamine intolerance

• Biogenic amines
• Ethylamines
• Imidazoles
• Immune system
• Vasodilators
• Immunostimulants
• Neurotransmitters