Secretin: digestive hormone & FDA-approved diagnostic drug
A natural gut hormone that tells the pancreas to release fluid that neutralizes stomach acid; also used as an FDA-approved diagnostic to test how well the pancreas works.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
What this is
Secretin is a 27-amino-acid hormone made in the small intestine that coordinates the digestive system's response to a meal. When partially digested food and acid arrive from the stomach into the duodenum, S cells lining the intestinal wall release secretin into the bloodstream. The hormone then travels to the pancreas, where it triggers a flood of bicarbonate-rich fluid that neutralizes the acid and creates the alkaline environment needed for digestive enzymes to work. Secretin holds a unique place in medical history: its discovery in 1902 by William Bayliss and Ernest Starling at University College London was the moment the concept of a "hormone" — a chemical messenger carried by the blood — was born. Synthetic human secretin (brand name ChiRhoStim) is FDA-approved as a diagnostic agent.
History
Bayliss and Starling made the discovery in a series of experiments on anesthetized dogs, showing that dilute hydrochloric acid instilled into a denervated loop of duodenum still caused the pancreas to secrete — proof that chemical, not neural, signaling was driving the response. They extracted the active substance from duodenal mucosa, called it secretin, and published their findings in the Journal of Physiology in 1902. Starling formally coined the word "hormone" (from the Greek hormaein, "to set in motion") three years later, in his 1905 Croonian Lectures to the Royal Society.
The molecular structure of secretin remained unknown for decades. Viktor Mutt and J. Erik Jorpes at the Karolinska Institutet spent years processing enormous quantities of porcine small intestine — reportedly ten kilometers of intestine to obtain the first milligram — and presented the amino acid sequence of porcine secretin at an IUPAC congress in Stockholm in 1966, with the full structural paper published in the European Journal of Biochemistry in 1970. The human secretin gene was subsequently cloned; it encodes a 120-amino-acid pre-prohormone from which the 27-residue active peptide is cleaved.
Regulatory recognition came more than a century after the discovery. The FDA approved SecreFlo (synthetic porcine secretin, manufactured by Repligen/ChiRhoClin) in April 2002 for pancreatic exocrine function testing. Synthetic human secretin — ChiRhoStim — received FDA approval in August 2004, adding gastrinoma diagnosis and ERCP papilla identification to the approved indications.
What it does
Secretin's central job is to neutralize the acid that enters the duodenum after a meal. It triggers pancreatic ductal cells to secrete large volumes of bicarbonate-rich fluid into the intestinal lumen, raising pH from the acidic range toward the neutral-to-alkaline range that digestive enzymes require. It also stimulates bicarbonate secretion from bile duct cells (cholangiocytes) in the liver, contributing to bile flow. At the same time, secretin inhibits gastric acid secretion and suppresses gastrin release, acting as a brake on the stomach once the small intestine signals that it has received enough acidic load.
Beyond the gut, secretin has roles in kidney water handling, where it promotes urinary bicarbonate and water excretion, and in the brain — secretin is expressed in the hypothalamus, hippocampus, cerebellum, and central amygdala. Research in mice lacking secretin or its receptor showed impaired hippocampal synaptic plasticity and social behavior. Work published in PNAS (2009) identified a role for secretin released from the posterior pituitary in regulating vasopressin expression and release under high-osmolality conditions, placing it at a control point for whole-body water homeostasis (Chey and colleagues, Pancreas 2014; Mavrych and colleagues, Frontiers in Aging 2026).
Evidence
- Human: FDA approval of ChiRhoStim rests on a clinical program covering 531 patients and 24 healthy volunteers, in which secretin stimulation was used diagnostically for pancreatic exocrine function, gastrinoma, and ERCP. Secretin-enhanced MR cholangiopancreatography (MRCP) is an established non-invasive imaging technique with sensitivity of 73–100% and specificity approaching 100% for pancreas divisum. For gastrinoma (Zollinger-Ellison syndrome), the secretin stimulation test reports approximately 85–90% sensitivity. Secretin for treatment of autism spectrum disorder was investigated in multiple randomized controlled trials; a Cochrane review encompassing 16 placebo-controlled RCTs with more than 900 children found no evidence of efficacy for autism symptoms, communication, or cognition.
- Animal: Secretin-knockout and secretin-receptor-knockout mice display impaired pancreatic bicarbonate secretion, abnormal hippocampal synaptic plasticity, altered social behavior, and dysregulation of water homeostasis, confirming the hormone's physiological roles across multiple organ systems (Chey and colleagues, Pancreas 2014).
- In vitro: Secretin activates cAMP production in pancreatic ductal cells and cholangiocytes through its cognate GPCR (SCTR), a well-characterized signaling response that underpins all approved diagnostic applications.
Known effects
- Pancreatic bicarbonate secretion — established physiological role; the basis of all approved diagnostic uses
- Inhibition of gastric acid secretion — documented endogenous function
- Bile flow stimulation — via large cholangiocytes; clinical use in secretin-enhanced MRCP
- Gastrinoma detection — FDA-approved diagnostic (secretin stimulation test; ~85–90% sensitivity)
- Pancreatic exocrine dysfunction assessment — FDA-approved diagnostic
- ERCP visualization — FDA-approved (papilla of Vater and accessory papilla identification)
- Autism spectrum disorder treatment — Investigated; no benefit demonstrated in 16 RCTs (Cochrane review)
- Water homeostasis / vasopressin modulation — Preclinical and mechanistic evidence; not a clinical indication
Safety signals
Secretin administered intravenously as a diagnostic agent has a very favorable safety record. In the ChiRhoStim clinical program (531 patients, 24 healthy volunteers), the most commonly reported adverse reactions were nausea, vomiting, flushing, and upset stomach, each occurring in fewer than 10 patients. Overall adverse event frequency across intravenous secretin use is reported below 5%. Acute pancreatitis following secretin administration during MRI has been observed at a rate of approximately 0.02% (2 per 10,000 patients); the FDA removed the requirement for a test dose in 2017 given the very low observed reaction rate. No allergic reactions were observed in clinical trials of the synthetic human form (ChiRhoStim), in contrast to earlier porcine-derived secretin products where allergic reactions were a theoretical concern. Secretin is prescription-only and administered intravenously in supervised clinical settings.
Regulatory status
- US: Prescription-only. FDA-approved as a diagnostic agent:
- SecreFlo (synthetic porcine secretin) — approved April 2002 for pancreatic exocrine dysfunction diagnosis - ChiRhoStim (synthetic human secretin) — approved August 2004; indications: pancreatic exocrine dysfunction, gastrinoma diagnosis, and ERCP papilla visualization
- EU: No centralized EMA approval on record for ChiRhoStim; secretin-based diagnostic preparations have been used in European clinical practice for pancreatic function testing, but regulatory status varies by member state
- WADA: Not listed on the WADA prohibited list; has no performance-enhancement application
Mechanism
Secretin is a member of the secretin-glucagon-VIP superfamily, a group of structurally related peptide hormones that includes glucagon, GLP-1, GIP, VIP, PACAP, and growth hormone-releasing hormone — all of which signal through Class B (secretin-family) GPCRs and act predominantly through cAMP. Secretin binds to the secretin receptor (SCTR), a seven-transmembrane Class B GPCR expressed on pancreatic ductal cells, cholangiocytes, gastric parietal cells, kidney tubules, and multiple brain regions. Binding activates Gαs, increasing intracellular cAMP and activating protein kinase A (PKA). In pancreatic ductal cells, PKA phosphorylates CFTR (the cystic fibrosis transmembrane conductance regulator), opening apical chloride channels; the resulting electrochemical gradient drives the Cl⁻/HCO₃⁻ exchanger AE2 to export bicarbonate into the ductal lumen, with water following osmotically (Chey and colleagues, Pancreas 2014). The stored 27-amino-acid sequence (HSDGTFTSELSRLREGARLQRLLQGLV) represents the mature active peptide; the C-terminal valine of native secretin carries an amide group (–NH₂) that is not encoded in the standard one-letter sequence shown here.
Related peptides
Secretin is the founding member of the secretin-glucagon superfamily. Closely related peptides that signal through Class B GPCRs include vasoactive intestinal peptide (VIP), which shares receptor-family architecture and a similar cAMP-driven signaling profile; glucagon-like peptide-1 (GLP-1), the basis of modern obesity and diabetes pharmacology; and glucose-dependent insulinotropic polypeptide (GIP). See also GLP-1 analogs on this platform.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Does secretin exist as a floppy, unstructured molecule in the bloodstream and only fold into its active shape at the moment it touches its receptor?
If true, this could explain why small pieces of secretin fail as drugs and would guide chemists toward making more stable versions that fold correctly on arrival. People needing SCTR-targeting treatments, such as those with pancreatic disease, could benefit from better-designed analogs.
Could chemically connecting two points in the middle of secretin's structure make it survive in the bloodstream long enough to be a real medicine?
Secretin currently breaks down in minutes, confining it to hospital-use diagnostics. If a stapled version lasted hours, it could become a daily or weekly treatment for patients with chronic pancreatic disease or short bowel syndrome, diseases with very limited drug options today.
Could secretin, released into the bloodstream after eating, also help prevent the immune cell accumulation that drives liver scarring diseases?
If true, an already-approved and well-tolerated hormone could be tested quickly in patients with fatty liver disease or early liver fibrosis, conditions affecting hundreds of millions of people worldwide with very few treatment options.
Could giving secretin, or a drug that mimics it, reduce the persistent low-level gut inflammation seen in older people?
Chronic gut inflammation in aging is linked to diabetes, heart disease, and cognitive decline. If secretin could reduce that inflammation, it might offer a simple gut-hormone-based way to support healthy aging for millions of older adults.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.8775342106819153 | boltz-2 |
| ranking score | 0.6502120494842529 | boltz-2 |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | colabfold_local |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-22 |
▸citationbibtex
@peptide{pep10752,
sequence = {HSDGTFTSELSRLREGARLQRLLQGLV},
target = {sctr},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}