Histamine (HIST)

Histamine is an organic nitrogenous compound that acts as a neurotransmitter and mediates local immune responses. It is synthesized from L-histidine and stored mainly in mast cells and basophils. Histamine is released in response to allergens or injury and exerts its effects by binding to four types of G protein-coupled receptors (H1, H2, H3, and H4). It plays key roles in inflammation, vasodilation, gastric acid secretion, and neurotransmission. Overproduction or inappropriate release of histamine underlies conditions like allergies, anaphylaxis, and foodborne illnesses. Therapeutic targeting involves antihistamines and epinephrine.

Histamine itself is not a drug, but drugs target its receptors to modulate its effects. Antihistamines block histamine receptors (primarily H1) to alleviate allergy symptoms or H2 receptors to reduce gastric acid secretion.