istamina

Istamina, or histamina in Italian, is a biogenic amine that participates in local immune responses, regulation of stomach acid, and neurotransmission. It is synthesized from the amino acid histidine by the enzyme histidine decarboxylase and is stored primarily in granules of mast cells and basophils, and in enterochromaffin-like cells in the stomach.

Upon release, histamine acts through four receptor subtypes—H1, H2, H3, and H4. Activation of H1 receptors on vascular endothelium and smooth muscle causes vasodilation, increased vascular permeability, itch, and bronchoconstriction. H2 receptors on gastric parietal cells stimulate acid secretion. H3 receptors, mainly in the brain and central nervous system, modulate neurotransmitter release and neuronal excitability. H4 receptors on immune cells influence chemotaxis and cytokine production.

Histamine is inactivated by enzymatic degradation, principally by diamine oxidase (DAO) in the gut and liver and by histamine-N-methyltransferase (HNMT) in various tissues. Metabolites are excreted in urine. Histamine intolerance can arise when degradation is reduced or intake exceeds capacity; symptoms can include flushing, headaches, gastrointestinal discomfort, and palpitations.

Clinical relevance and management: In allergic reactions and anaphylaxis histamine contributes to edema, itching, and bronchospasm. Antihistamines block H1 receptors; H2 blockers reduce gastric acid secretion. Research on H3 and H4 antagonists focuses on central nervous system disorders and inflammatory diseases. Dietary considerations may involve avoiding histamine-rich foods and agents that inhibit DAO for susceptible individuals.