Gastrin, is a hormone that normally formed by mucosal cells in the gastric antrum and by the D cells of the pancreatic islets. Its primary function is to stimulate secretion of HCl by the gastric mucosa. HCl, in turn, inhibits gastrin formation. It also responsible for stimulating smooth muscle contraction and increasing blood circulation and water secretion in the stomach and intestine. Gastrin is regulated by epidermal growth factor in both mice and humans. Gastrin is excreted in excess by pancreatic tumors in the Zollinger-Ellison syndrome. Gastrin-Releasing Peptide (GRP) stimulates the release of gastrin as well as other gastrointestinal hormones and also acts as an autocrine growth factor for certain cell types. High levels of GRP are found in the human lung just after birth and levels decrease thereafter in parallel with the observed disease in a number of pulmonary neuroendocrine cells. GRP is known to promote lung tumorigenesis in model systems.