Secretin (ChiRhoStim)

Prescription

Secretin holds a special place in medical history: identified in 1902 by Bayliss and Starling, it was the very first substance shown to act as a hormone — a chemical messenger released into the blood by one organ to act on another. It is a 27-amino-acid peptide released by cells of the duodenum when acidic chyme arrives from the stomach. Its natural job is to signal the pancreas and biliary system to release a watery, bicarbonate-rich fluid that neutralizes stomach acid and creates the right environment for digestive enzymes. Today synthetic human secretin (brand name ChiRhoStim) is used as a diagnostic agent. In pancreatic function testing, secretin is given intravenously and the resulting pancreatic secretions are collected (traditionally via a duodenal tube, or assessed with secretin-enhanced MRCP imaging) to measure bicarbonate output — a direct readout of exocrine pancreatic function useful in evaluating chronic pancreatitis and unexplained pancreatic insufficiency. A second important use is in the diagnosis of gastrinoma (Zollinger-Ellison syndrome), a gastrin-secreting tumor that causes severe acid-related ulcers. Paradoxically, in patients with gastrinoma, injected secretin causes a sharp rise in serum gastrin (whereas in normal individuals it suppresses or minimally changes gastrin). This 'secretin stimulation test' — measuring gastrin before and after secretin — is a well-established way to confirm the diagnosis. Mechanistically secretin binds the secretin receptor (a class B G-protein-coupled receptor) on pancreatic duct cells and, in gastrinomas, on the tumor cells. It is given as a single intravenous dose for testing and is generally well tolerated; transient flushing or nausea can occur. The tests and their interpretation are performed by gastroenterologists as part of a targeted workup.