Gastrin is a 17-residue polypeptide isolated from the antralmucosa. It was isolated originally in two different forms. Inone of the forms, the tyrosine residue in position 12 is sulfated.Both forms are biologically active. Cholinergic responseto the presence of food in the gastrointestinal tract providesthe stimulus for gastrin secretion. The lowering of pHin the stomach inhibits the secretion of gastrin. The effects ofstructural modification of gastrin on gastric acid secretionhave been reviewed. These studies revealed that the fourresidues at the COOH terminus retain significant biologicalactivity and that the aspartate residue is the most critical foractivity. The most important action of gastrin is to stimulatethe secretion of gastric acid and pepsin. Other actions of gastrininclude increased secretion of pancreatic enzymes; contractionof smooth muscles; water and electrolyte secretion bythe stomach and pancreas; water and electrolyte absorption bythe small intestine; and secretion of insulin, glucagon, and somatostatin.A synthetic pentapeptide derivative, pentagastrin,is currently used as a gastric acid secretagogue.
Clinical Use
The plasma concentration of gastrin is measured by
RIA or ELISA,11 and can be used to diagnose gastrinsecreting tumors, atrophic gastritis, gastric ulcers, and
pernicious anemia. The gastrin test is performed to estimate acid secretory capacity and assess the extent of surgical vagotomy. It is also used to stimulate bioactive
neuropeptide secretion in patients with neuroendocrine
tumors such as vasoactive intestinal polypeptide secreting tumors.
