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Histamine and its agonists Histamine antagonists H1 receptor antagonists H2 receptor antagonists Histamine ?Introduction Histamine is biologically active amine that is found in many tissue (such as mast cells or basophils ),has plex physiologic and pathologic effects, and is often released locally. Together with endogenous peptides, prostaglandins and leukotrienes, and cytokines, they are sometimes called autacoids or local hormones Histamine receptor subtypes Receptor Subtype Distribution Postreceptor Mechanism H1 Smooth muscle, endothelium, brain ↑ IP3,DAG H2 Gastric mucosa, cardiac muscle, mast cells, brain ↑ cAMP H3 Presynaptic: brain, myenteric plexus, other neurons G proteincoupled Histamine receptor subtypes Receptor Subtype Effects after being activated H1 bronchoconstriction and contraction of intestinal . Expand blood vessel Permeability↑ stimulate sensory nerve endings H2 Cause gastric acid, gastric pepsin and intrinsic factor production. Cause a dec