The H2 subclass of histamine receptors mediates gastric acid secretion. Also appears to regulate gastrointestinal motility and intestinal secretion. Possible role in regulating cell growth and differentiation. The activity of this receptor is mediated by G proteins which activate adenylyl cyclase and, through a separate G protein-dependent mechanism, the phosphoinositide/protein kinase (PKC) signaling pathway (By similarity). Antagonists for this receptor have proven to be effective therapy for acid peptic disorders of the gastrointestinal tract. Certain antagonists are used in the treatment of neuropsychiatric and neurological diseases such as schizophrenia, Alzheimer disease and Parkinson disease. Belongs to the G-protein coupled receptor 1 family. H2 receptor entry