Gastrin, also known as pepsin, is a gastrointestinal hormone mainly secreted by G cells of gastric antrum and duodenum and plays an important role in regulating digestive tract function and maintaining intact structure of digestive tract. Gastrin can promote gastric acid secretion, facilitate growth of gastrointestinal mucosal cells, and improve nutrition and blood supply of mucosa. In human body, more than 95% of biologically active gastrin is α-amidated gastrin, which mainly contains two isomers: G-17 and G-34. G-17 shows the highest content in human body (about 80%~90%). Secretion of G-17 is strictly controlled by pH value of gastric antrum and shows negative feedback mechanism that relative to gastric acid.