Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. Its various actions are mediated by histamine receptors H1, H2, H3, and H4. Specifically, the histamine receptor H2 belongs to the rhodopsin-like family of G protein-coupled receptors. As an integral membrane protein, it stimulates gastric acid secretion and regulates gastrointestinal motility and intestinal secretion and is thought to be involved in regulating cell growth and differentiation.