Gastrin is mainly known by its first described role as a gastric acid-hormone but the protein also has the ability to promote cellular growth. More recently, gastrin has been suggested to induce leukocyte-endothelial cell interactions and to have a pro-inflammatory effect. Gastrin has two biologically active peptide forms, G34 and G17 and they activate two different receptors: the CCK-1 receptor, which has low affinity for gastrin but high affinity for the related hormone cholecystokinin (CCK), and the CCK-2 receptor, which has high affinity for both gastrin and CCK and mediates the acid-secretory as well as the proliferative effects of gastrin.