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Biosynthesis, function and effect
histamine is a widespread biogenic amine in the animal and plant kingdom. In the human body, it acts both as a hormone and as a neurotransmitter.
In its function as a hormone histamine is very versatile: it is the main messenger in natural defense reactions of the body, e.g. at the onset of itching, allergies and inflammatory reactions. The effect of histamine as a neurotransmitter, on the other hand, has not yet been completely clarified. However, histamine involvement has been shown to be beneficial in controlling the day-night rhythm and inducing vomiting. Furthermore, by its inhibitory (inhibitory) action, histamine also indirectly affects nerve cells of acetylcholine, dopamine, glutamine, norepinephrine and serotonin by decreasing the release of other neurotransmitters.
The biosynthesis of histamine (C5H9N3) is made from the essential amino acid histidine (C6H9N3O2). The catalyst used here is the enzyme histidine decarboxylase. Within this one-step reaction process, the histidine becomes a CO2Molecule split off (decarboxylation). Because histamine is a tissue hormone, histamine synthesis occurs in virtually all body tissue, including the histaminergic nerve cells in the brain.
In animals and plants, histamine is often produced as an antidote to predators: thus injecting e.g. Honey bees and stinging nettles give their "attacker" a liquid containing histamine (maximum 0.5-1% histamine), which causes an inflammatory reaction in the attacker. In addition, additional enzymes in the liquid promote the release of the body's own histamine. Anti-allergenic drugs, called antihistamines, can block the release by blocking histamine receptors.