Since the discovery of histamine in 1910 there has been growing evidence that this biogenic amine, which is mainly synthesized by mast cells and basophils, is released
in inflammatory processes, and plays a fundamental role in the pathogenesis of allergic rhinitis.
Histamine is a biogenic amine found in many body tissues and cells. It is synthesized from the amino acid L-histidine through mediation of the enzyme L-histidine decarboxylase, while its metabolism is mediated by the enzyme histamine N-methyltransferase, or alternatively by diamino-oxidase. Histamine is an important chemical messenger with stimulatory action (agonism) upon at least four types of receptors, and with multiple regulatory functions in the nervous system, gastrointestinal tract and immune system. All histamine receptors transmit the corresponding extracellular signals via protein G systems coupled to intracellular second messengers. The activation of one of these messengers, specifically guanosine triphosphate (GTP) – binding protein, triggers a cascade of events at intracytoplasmic level that ultimately induce activation of the kappa nuclear factor (NF-κ). The latter is an important proinflammatory transcription factor that exerts its function by binding to the promoter regions of genes – thereby stimulating the synthesis of a large number of mediators

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