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histamine

  (hĭs'tə-mēn', -mĭn)

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A physiologically active amine, C₅H₉N₃, found in plant and animal tissue and released from mast cells as part of an allergic reaction in humans. It stimulates gastric secretion and causes dilation of capillaries, constriction of bronchial smooth muscle, and decreased blood pressure.

[HIST(IDINE) + AMINE.]

A biologically active amine that is formed by the decarboxylation of the amino acid histidine. It is widely distributed in nature and is found in plant and animal tissues as well as in insect venoms. In humans, histamine is a mediator of inflammatory reactions, and it functions as a stimulant of hydrochloric acid secretion in the stomach.

Most tissue histamine is found stored in mast cells, where it can be released by a variety of stimuli. Once released, it can cause many effects, including constriction of bronchiolar, gastrointestinal, uterine smooth muscle, and lowering of blood pressure. If histamine is released in the skin, itching, a flare (area of redness) due to vasodilation, and a wheal due to leaking of fluid into the tissue are observed. The increase in vascular permeability that permits this leakage is due to an action on the endothelial cells of postcapillary venules.

All of these actions of histamine are mediated by the activation of histamine receptors, designated either H-1 or H-2. Antihistamine drugs exert their effects by blocking the combination of histamine with these receptors. See also Antihistamine.

Histamine release can be caused by tissue injury, by physical stimuli such as cold or pressure, by drugs such as heroin, and most importantly by immunologic mechanisms. Mast cells in the skin, the lung, the nasal passages, or other sites may become sensitized to antigens such as ragweed or other pollens, and then release histamine and other biologically active substances upon exposure to them. The released histamine may then cause the effects commonly associated with allergic responses. If the allergic reaction becomes generalized and severe, life-threatening anaphylactic shock may ensue. The prompt administration of epinephrine, which exerts effects opposite to those of histamine, can be life-saving in such cases. See also Allergy; Antigen; Epinephrine; Hypersensitivity; Immunology.

The amine formed by decarboxylation of the amino acid histidine in the body, also found in small amounts in cheeses, beer, chocolate, sauerkraut, and wines. Excessive release of histamine from mast cells is responsible for many of the symptoms of allergic reactions. It also stimulates secretion of gastric acid, and administration of histamine provides a test for achlorhydria.

Histamine, a chemical derived from the amino acid histidine, has been implicated in a number of disorders. It is a transmitter of nerve impulses secreted by the hypothalamus in the brain. In addition to its function in the nervous system, it is released from body tissues during allergic reactions. Release into the skin causes nettle rash; release in the lungs contributes to asthma. Certain foods, such as chocolate, fish, and strawberries may stimulate immune cells (mast cells) to secrete histamine in sensitized individuals. This may be responsible for some cases of food intolerance.

A compound found in all cells that is produced by the breakdown of histidine. Histamine is released in allergic, inflammatory reactions and causes dilation of capillaries, decreased blood pressure, increased secretion of gastric juice, and constriction of smooth muscles of the bronchi and uterus.

For more information on histamine, visit Britannica.com.

An endogenous substance responsible for some allergic responses in the eyes, nose, and skin (e.g. during a bout of hay fever). It is formed in the body from histidine. Histamine is released by mast cells in most tissues during inflammation. It is also secreted by some areas of the hypothalamus and functions as a metabotropic neurotransmitter belonging to the biogenic amines. It acts as a powerful vasodilator and increases the permeability of blood vessels.

An amine, C₅H₉N₃, produced by decarboxylation of histidine, found in all body tissues.
It induces capillary dilatation, which increases capillary permeability and lowers blood pressure; contraction of most smooth muscle tissue; increased gastric acid secretion; and acceleration of the heart rate. It is also a mediator of immediate hypersensitivity. There are two types of cellular receptors of histamine: H₁-receptors, which mediate contraction of smooth muscle and capillary dilatation; and H₂-receptors, which mediate acceleration of heart rate and promotion of gastric acid secretion. Both H₁- and H₂-receptors mediate the contraction of vascular smooth muscle. Histamine may also be a neurotransmitter in the central nervous system. It is used as a diagnostic aid in testing gastric secretion and in the diagnosis of pheochromocytoma.
There are two types of histamine antagonists that act at either the H₁- or the H₂-receptors. Drugs such as diphenhydramine and chlorpheniramine are referred to as antihistamines or H₁-blockers; they block the effects of histamine on vascular, bronchial and gastrointestinal smooth muscle and on capillary permeability. They are used for relief of allergic and gastrointestinal disorders. Drugs such as cimetidine (Tagamet) are referred to as H₂-blockers; they block the stimulation of gastric acid secretion and are used to treat gastrointestinal ulceration.

• h.-containing foods — some food sources, particularly some species of fish, have high levels of histamine; increased levels can also occur from improper storage which permits conversion of histidine to histamine, and an excessive carbohydrate content may promote bacterial growth, fermentation and production of histamine.
• h.-releasing foods — some foods can cause release of histamine from mast cells; these include egg white, shellfish and fish.
• h. shock — manipulation and particularly surgical trauma to large mast cell tumors may lead to decreased blood pressure and persistant bleeding caused by the release of histamine and vasoactive amines.

Histamine
IUPAC name	2-(3H-imidazol-4-yl)ethanamine
Identifiers
CAS number	51-45-6
PubChem	774
MeSH	Histamine
SMILES	C1=C(NC=N1)CCN
Properties
Molecular formula	C5H9N3
Molar mass	111.145
Melting point	83.5 °C (182.3 °F)
Boiling point	209.5 °C (409.1 °F)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Histamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter.^[1] New evidence also indicates that histamine plays a role in chemotaxis of white blood cells.

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.

Conversion of histidine to histamine by histidine decarboxylase

Once formed, histamine is either stored or rapidly inactivated. Histamine released into the synapses is broken down by acetaldehyde dehydrogenase. It is the deficiency of this enzyme that triggers an allergic reaction as histamines pool in the synapses. Histamine is broken down by histamine-N-methyltransferase and diamine oxidase. Some forms of foodborne disease, so-called "food poisonings," are due to conversion of histidine into histamine in spoiled food, such as fish.

Storage and release

Mast cells

Most histamine in body tissue is found in granules in mast cells (see figure) or 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, including such drugs as morphine and tubocurarine, can displace histamine in granules and cause its release.

Mechanism of action

Histamine exerts its actions by combining with specific cellular receptors located on cells. The four histamine receptors that have been discovered are designated H1 through H4.

Type	Location	Function
H1 histamine receptor	Found on smooth muscle, endothelium, and central nervous system tissue	Causes vasodilation, bronchoconstriction, smooth muscle activation, separation of endothelial cells (responsible for hives), and pain and itching due to insect stings; the primary receptors involved in allergic rhinitis symptoms and motion sickness.
H2 histamine receptor	Located on parietal cells	Primarily regulate gastric acid secretion
H3 histamine receptor	-	Decreased neurotransmitter release: histamine, acetylcholine, norepinephrine, serotonin
H4 histamine receptor	Found primarily in the thymus, small intestine, spleen, and colon. It is also found on basophils and in the bone marrow.	Unknown physiological role.

Roles in the body

Sleep regulation

Histamine is released as a neurotransmitter. The cell bodies of neurons which release histamine are found in the posterior hypothalamus, in various tuberomammillary nuclei. From here, these histaminergic 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 (which stimulate histamine release) 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.

Sexual response

Research has shown that histamine is released as part of the human orgasm from mast cells in the genitals. If this response is lacking this may be a sign of histapenia (histamine deficiency). In such cases, a doctor may prescribe diet supplements with folic acid and niacin (which used in conjunction can increase blood histamine levels and histamine release), or L-histidine. Conversely, men with high histamine levels may suffer from premature ejaculations.

Schizophrenia

It has been found that about half the patients classified as suffering from schizophrenia have low histamine levels in the blood.^[2] This may be because of antipsychotics that have unwanted effect on histamine, such as Quetiapine. Although, in these cases, as histamine levels were increased, their health improved.

Disorders

High or low histamine levels are considered by some of the alternative medicine community to be health issues; this is not accepted by the mainstream medical community. However, as an integral part of the immune system it 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

• Antihistamine
• Basophil
• Mast cell
• Allergy
• Atopy

References

1. ^ Marieb, E. (2001). Human anatomy & physiology. San Francisco: Benjamin Cummings, 414. ISBN 0-8053-4989-8. 
2. ^ What is Schizophrenia?

External links

• DrugBank EXPT01785

Autacoids
Angiotensin - Eicosanoid - Histamine - Kinin - Platelet-activating factor - Serotonin

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - histamin

Nederlands (Dutch)
histamine (medicijn)

Français (French)
n. - histamine

Deutsch (German)
n. - Histamin

Ελληνική (Greek)
n. - (βιολ.) ισταμίνη

Italiano (Italian)
istamina

Português (Portuguese)
n. - histamina (f) (Quím.)

Русский (Russian)
гистамин

Español (Spanish)
n. - histamina

Svenska (Swedish)
n. - histamin (hormon i kroppens vävnader som frigörs vid överkänslighetsreaktioner)

中文（简体） (Chinese (Simplified))
组织胺

中文（繁體） (Chinese (Traditional))
n. - 組織胺

한국어 (Korean)
n. - 히스타민

日本語 (Japanese)
n. - ヒスタミン

العربيه (Arabic)
‏(الاسم) الهستامين, مركب يكون في الارغوت وفي كثير من الانسجه الحيوانيه‏

עברית (Hebrew)
n. - ‮תרכובת המכווצת שרירים ומרחיבה כלי-דם שמשחררים תאים בגוף בעת פציעה, היסטמין‬

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