Pharmacology of Histamine

Histamine has a wide spectrum of actions involving many organs and organ systems. These effects include actions on smooth muscle vascular endothelium afferent nerve terminals heart gastrointestinal tract and CNS. On smooth muscle histamine causes some muscle fibers to contract and others to relax. Histamine plays a major role in the pathophysiology of allergic diseases including rhinitis urticaria asthma and anaphylaxis. Histamine exerts its effects through its interaction with one of four distinct receptors (H1 H2 H3 H4). In a localized allergic reaction an allergen (antigen) first penetrates an epithelial surface (e.g. skin nasal mucosa). The allergen can also be delivered systemically as in the case of an allergic response to penicillin. With the aid of T-helper (T H ) cells the allergen stimulates B lymphocytes to produce IgE antibodies that are specific for that allergen.