Histamine, one of the most important mediators of allergy and inflammation. Histamine is synthesized in a restricted population of neurons located in the tuberomammillary nucleus of the posterior hypothalamus implicated in many brain functions (e.g. sleep/wakefulness, hormonal secretion, cardiovascular control, thermoregulation, food intake, and memory formation). In peripheral tissues histamine is stored in mast cells, basophils, enterochromaffin cells. Histamine release leads to various well-known symptoms of allergic conditions in the skin and the airway system. Histamine effects are mediated by four pharmacologically distinct receptors, the H1R, H2R , H3R and H4R receptors. Histamine receptors display 7 TM domains, an extracellular N-terminus, and a cytoplasmic C-terminus of variable length. H1R (mouse 488 aa; rat 486 aa; human 487 aa, chromosome 3p21-p14; ~75-85% interspecies homology) is distributed in the brain, most smooth muscle cells, endothelial cells, adrenal medulla, and heart. H1R plays roles in smooth muscle contraction, stimulation of nitric oxide formation, endothelial cell contraction, and increasing vascular permeability, all of which have close relationships with allergic conditions. H1R preferentially couples to the Gq/11 family of G-proteins and causes mobilization of intracellular Ca 2+ in a pertussis toxin-insensitive fashion. Compounds such as mepyramine (pyrilamine) and triprolidine are highly potent H1 antagonists, and easily penetrate the brain causing sedation. Many new non-sedating H1 antagonists (e.g. cetirizine, etc), are used to treat allergic conditions).
Intended for research use only. Not for use in human, therapeutic, or diagnostic applications.