White to slightly yellow powder
Histamine is an important protein involved in many allergic reactions. Allergies are caused by an immune response to a normally innocuous substance (i.e. pollen, dust) that comes in contact with lymphocytes specific for that substance, or antigen. The history of histamine and the development of antihistamines have been reviewed in [Drugs of Today (1986) and the Journal of Allergy & Clinical Immunology]. Histamine was the first to be characterized of a series of biogenic amines that are released in the inflammatory process. As early as 1910, it was shown that histamine caused constriction of isolated guinea pig ileum and, subsequently, it was found that histamine induced a shock-like syndrome. In 1927 the presence of histamine in normal tissues was demonstrated. Attempts to reduce histamine manifestations led to the report, in 1933, that certain phenolic ethers inhibited histamine action. Toxicity precluded clinical use. In 1942 phenbenzamine (Antergan), C17H22N2, was the first antihistamine to be successfully used in humans.
In 1966, the name H1 was proposed for receptors blocked by the at that time known antihistamines. It was also speculated that the other actions of histamine were likely to be mediated by other histamine receptors. The existence of the H2 receptor was accepted in 1972 and the H3 receptor was recognized in rat brain in 1983. H3 receptors in the brain appear to be involved in the feedback control of both histamine synthesis and release, whereas release of various other neurotransmitters, eg, serotinin (5-HT), dopamine, noradrenaline, and acetylcholine, is also modulated. H3 receptor effects have also been demonstrated in various peripheral tissues and H3 agonists and antagonists are undergoing intensive study for therapeutic applications.
H1&2 agonist, edema induction, gastric secretion stimulant
Histamine inhibits the synthesis of IL-2 and γ-IFN in peripheral blood mononuclear cells and lipopolysaccharide-induced synthesis of TNF-α in monocytes via H2?receptor activation. It is a powerful stimulant of gastric secretion, a constrictor of bronchial smooth muscle, a vasodilator, and also a centrally acting neurotransmitter.
Sinus problems, hay fever, bronchial asthma, hives,
eczema, contact dermatitis, food allergies, and reactions
to drugs are all allergic reactions associated with the release
of histamine and other autocoids, such as serotonin,
leukotrienes, and prostaglandins. Histamine release
is frequently associated with various inflammatory
states and may be increased in urticarial reactions, mastocytosis,
and basophilia. Histamine also acts as a neurotransmitter
in the central nervous system (CNS).
Upon release from its storage sites, histamine exerts effects
ranging from mild irritation and itching to anaphylactic
shock and eventual death.
ChEBI: A member of the class of imidazoles that is 1H-imidazole substituted at position C-4 by a 2-aminoethyl group.
Virtually all of the histamine found in individual organs
and tissues is synthesized locally and stored in subcellular
secretory granules. Within the tissues, the mast cells
are the principal sites of storage; in the blood, the basophils serve this function. Histamine is also present in
neurons of the CNS, where it acts as a neurotransmitter.
Histamine is synthesized from the amino acid histidine
by an action of the enzyme histidine decarboxylase. Following synthesis, histamine is either rapidly
inactivated or stored in the secretory granules of
mast cells and basophils as an inactive complex with
proteases and heparin sulfate or chondroitin sulfate.
Histamine occurs in the brain, particularly in certain
hypothalamic neurons, and evidence is strong that histamine
is a neurotransmitter. Distribution of histamine,
its synthetic enzyme (histidine decarboxylase), and
methyl histamine (the major brain metabolite) is not
uniform. Possible roles for histamine in the regulation
of food and water intake, thermoregulation, hormone
release, and sleep have been suggested.
Histamine is a neurotransmitter produced by neurons of the posterior hypothalamus. In the brain, histamine is predominantly present in the gray matter.
Histamine participates in innate and acquired immune response, mediating allergy and inflammation. It helps in intestinal muscle contraction. During anaphylactic shock histamine causes bronchial constriction. Histamine is also involved in gastric acid secretion, epithelial and endothelial barrier control.
Non–Antigen-Mediated Release of Histamine
Histamine may be released from mast cells by mechanisms
that do not require prior sensitization of the immune
system. Drugs, high-molecular-weight proteins,
venoms, and other substances that damage or disrupt
cell membranes can induce the release of histamine.
Any thermal or mechanical stress of sufficient intensity
also will result in histamine release. Cytotoxic compounds,
may release histamine as the result of disruption
of cell membranes.
Histamine is found in animal tissues and venoms and
in many bacteria and plants.Within the human body, the
largest histamine concentrations are in the skin, lungs,
and gastrointestinal mucosa, while concentrations are
smaller in almost all other organs and tissues.Histamine
is present in human plasma at relatively low concentrations
(usually less than 0.5 ng/mL); in contrast, wholeblood
levels can be as high as 30-fold greater. Substantial
quantities of histamine are present in urine, with excretion
rates varying from 10 to 40μg per 24 hours.
Histamine has only minor uses in clinical medicine. In
the past it was used to diagnose pernicious anemia, in
which histamine fails to evoke the usual secretion of
gastric acid. Histamine has been used to assess
bronchial hyperreactivity, although this test may be
quite hazardous for asthmatics. Today the main clinical
use of histamine is as a positive control injection for allergy
skin testing.
Sedation is the most frequent adverse reaction to the
first-generation antihistamines. An additive effect on
alertness and motor skills will result if alcohol or another
depressant is taken with these drugs. Antimuscarinic
effects caused by these drugs include dry
mouth and respiratory passages, urinary retention, and
dysuria. Nausea, vomiting, constipation or diarrhea,
dizziness, insomnia, nervousness, and fatigue also have
been reported. Drug allergy, especially after topical application,
is fairly common.Tolerance to certain antihistamines
may develop after prolonged administration.
Teratogenic effects of the piperazine antihistamines
have been shown in animal studies. Epidemiological studies have not shown such an association in humans.
The effects of toxic doses of first-generation antihistamines,
similar to those seen following atropine administration,
include excitement, hallucinations, dry mouth,
dilated pupils, flushing, convulsions, urinary retention,
sinus tachycardia, coma, and death.
The second-generation H1-antagonists are often referred
to as nonsedating antihistamines; however, doses
above the usual therapeutic level can cause sleepiness
in certain individuals.A more serious adverse effect of
some earlier second-generation antihistamines is cardiotoxicity.
Histamine is synthesized in tissues by decarboxylation of amino acid L-histidine, a process
catalyzed by the pyridoxalphosphate-dependent enzyme L-histidinedecarboxylase.
Histamine can enter the organism with food; it also can be generated by bacteria of the gastrointestinal tract.
It crystallises from *benzene or chloroform. [Beilstein 25 I 628, 25 II 302, 25 III/IV 2049.]
