About cimetidinehistamine h2-receptor antagonist, antiulcer.mechanism of action of cimetidinecimetidine is a h2 (histamine) receptor antagonist.histamine is the most potent stimulus of acid secretion and acts as the common mediator. h2 receptor is a g-protein coupled receptor. it induces adenylate cyclase which converts atp to cyclic amp. this cyclic amp acts on proton pump and exchange extracellular potassium ion for intracellular hydrogen ion across the parietal cell membrane. cimetidine reversibly competes with histamine for binding to h2 receptors on the basolateral membrane of parietal cells and predominantly inhibits basal acid secretion.