Histamina

Histamine is an organic amine that functions as both a neurotransmitter in the central nervous system and a mediator of inflammatory and immune responses in peripheral tissues. It is synthesized from the amino acid histidine by the enzyme histidine decarboxylase and stored in granules of mast cells, basophils, and certain enterochromaffin-like cells in the gut.

Histamine exerts its effects through four G protein–coupled receptors, designated H1, H2, H3, and H4. H1 receptors are involved in vasodilation, increased vascular permeability, bronchoconstriction, and allergic symptoms. H2 receptors regulate gastric acid secretion by parietal cells and influence heart rate and vascular tone. H3 receptors act as presynaptic autoreceptors and modulate neurotransmitter release in the brain, while H4 receptors are expressed on various immune cells and participate in inflammatory responses. Histamine release is triggered by physical injury, allergens that cross-link IgE on mast cells, or other stimuli, leading to symptoms such as redness, swelling, itching, and, in severe cases, anaphylaxis.

Metabolism of histamine occurs primarily through diamine oxidase (DAO) and histamine N-methyltransferase (HNMT). DAO degrades extracellular histamine, especially in the gut and placenta, while HNMT acts intracellularly in many tissues. Impaired breakdown can lead to histamine accumulation, contributing to histamine intolerance in some individuals.

Clinical relevance includes allergic reactions, rhinitis, urticaria, gastric ulcers, and certain inflammatory conditions. Treatments often target histamine receptors using antihistamines (H1 blockers) or, for gastric acid reduction, H2 receptor antagonists. Diet and gut health can influence histamine levels, as ferments and aged foods may contain or release histamine.