Secretin: The First Hormone
| Category | Research |
|---|---|
| Also known as | secretin history, Bayliss Starling, first hormone discovered |
| Last updated | 2026-04-14 |
| Reading time | 3 min read |
| Tags | historysecretinfirst-hormonebayliss-starlinggut-peptides |
Overview
Secretin, a 27-amino-acid peptide produced by intestinal S-cells, occupies a unique place in medical history as the first molecule ever shown to act as a "hormone." In 1902, the British physiologists William Bayliss and Ernest Starling, working at University College London, demonstrated that acidified extracts of duodenal mucosa, when injected into the bloodstream, stimulated pancreatic secretion. Because the effect persisted even when all nerves to the pancreas were cut, Bayliss and Starling concluded that a chemical messenger carried in the blood — not a nerve — coordinated the response.
Three years later, in 1905, Starling coined the word "hormone," from the Greek "hormao" (to urge on), in a Croonian lecture at the Royal College of Physicians. The term has named the field of endocrinology ever since.
Secretin was eventually purified and sequenced, revealing it as a member of the secretin/glucagon family that also includes glucagon, VIP, GIP, PACAP, and GLP-1. All of these peptides share a common ancestral gene, an N-terminal histidine in several cases, and similar G protein-coupled receptors.
Key People
- William Maddock Bayliss (1860–1924): British physiologist who co-discovered secretin.
- Ernest Henry Starling (1866–1927): British physiologist who coined the word "hormone."
- Viktor Mutt and Erik Jorpes: Karolinska biochemists who later purified and sequenced secretin.
- Claude Bernard (1813–1878): Nineteenth-century French physiologist whose "internal secretion" concept anticipated the hormone idea.
Timeline
- 1825: Claude Bernard begins work on the "internal secretion" of the pancreas.
- 1902: Bayliss and Starling demonstrate the chemical nature of the duodeno-pancreatic reflex.
- 1905: Starling introduces the word "hormone."
- 1961: Jorpes and Mutt report purification of secretin.
- 1965: Secretin's amino acid sequence is established.
- 1975: Secretin becomes a clinical test agent for pancreatic function.
- 1991: Secretin receptor is cloned.
Background
The historical significance of the Bayliss-Starling experiment is that it settled a long-running debate about how the body coordinates physiological responses. Ivan Pavlov and other prominent physiologists of the era favored a purely neural explanation, while some French and German investigators suspected chemical messengers. Bayliss and Starling's elegant demonstration that denervated intestines could still signal the pancreas through the blood established the hormonal concept and, with it, the modern field of endocrinology.
Mechanistically, secretin is released from S-cells in response to acidic chyme entering the duodenum. It stimulates the pancreatic ductal cells to secrete bicarbonate-rich fluid, neutralizing the acid and protecting the duodenal mucosa. It also inhibits gastric acid secretion, creating a classical negative-feedback loop.
Modern Relevance
Synthetic secretin (ChiRhoStim) is used clinically as a diagnostic tool. It is injected to provoke pancreatic enzyme and bicarbonate secretion during magnetic resonance cholangiopancreatography, to stimulate gastrin release in the evaluation of Zollinger-Ellison syndrome, and as part of certain pancreatic function tests. Its diagnostic niche is narrow but well established.
Research on secretin continues in several directions. The secretin/glucagon/VIP receptor family is a fertile area for drug discovery, as illustrated by the success of GLP-1 receptor agonists and dual agonists such as tirzepatide. Secretin itself has been studied for conditions ranging from autism (claims that were ultimately not supported by controlled trials) to heart failure, reflecting an ongoing search for new indications. For the broader story of gut peptides, see cck-discovery and gastrin-discovery.
Related Compounds
Related entries
- The Discovery of Cholecystokinin— Cholecystokinin, the gut peptide that triggers gallbladder contraction and pancreatic enzyme release, was identified by Ivy and Oldberg in 1928.
- Ernest Starling— Ernest Starling was the British physiologist who coined the word 'hormone' in 1905 and, with William Bayliss, discovered secretin.
- The Discovery of Gastrin— Gastrin, the stomach hormone that drives gastric acid secretion, was proposed by Edkins in 1905 and purified by Gregory and Tracy in the 1960s.