Gastrin is a peptide hormone coded at 7q12-q21 with two active forms in man:
- Gastrin I
- Seventeen amino acids Glp-Gly-Pro-Trp-Leu-Glu-Glu-Glu-Glu-Glu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2
- Gastrin II
- sulfate ester group on tyrosine in the 12th position of gastrin I
It is produced by the gastric antral mucosal G cells and to a lesser extent by the D cells of the pancreatic islets. Release is stimulated by gastrin-releasing polypeptide(GRP), a secretagogue from the neurons in the antral mucosa, which also stimulates the release of pancreatic polypeptide, glucagon, gastric inhibitory peptide and insulin.
Its main function is to stimulate H+ ion excretion by the oxyntic gastric mucosa, which in turn inhibits gastrin secretion by mucosal cells of the antrum.
A number of synthetic active analogues exist including:
Somatostatin, which is secreted by D cells, including those of the oxyntic mucosa, controls G cell gastrin secretion by modification of its gene transcription.