Secretin

Secretin is a 27-amino acid gastrointestinal hormone produced by S-cells of the duodenum in response to acidic chyme. As the first hormone ever discovered (1902), it stimulates pancreatic bicarbonate secretion and bile flow. ChiRhoStim is the FDA-approved synthetic human secretin used diagnostically for exocrine pancreatic function testing, ERCP facilitation, and Zollinger-Ellison syndrome diagnosis.

Secretin binds the secretin receptor (SCTR), a class B GPCR expressed on pancreatic ductal cells, bile duct cells, and gastric mucosa. Receptor activation increases intracellular cAMP via Gs coupling, stimulating pancreatic acinar cells to secrete bicarbonate-rich fluid into the duodenum to neutralize gastric acid. Secretin also inhibits gastrin release, reducing gastric acid secretion. In the liver, it promotes bile bicarbonate secretion. Central actions include modulating satiety and water homeostasis.

Secretin has over a century of clinical use as a diagnostic agent. The FDA approved ChiRhoStim (synthetic human secretin) for exocrine pancreatic function testing, ERCP facilitation, and Zollinger-Ellison syndrome diagnosis. Exploratory research has investigated secretin in autism spectrum disorder, though results from randomized trials have been inconsistent and it is not approved for this indication. Animal studies suggest roles in neurogenesis and neuroprotection.