Gastrin-17: the stomach's acid-release hormone

What this is

Gastrin-17 (G-17) is the short, active form of gastrin — a hormone made by specialised "G cells" lining the antral (lower) region of the stomach. When a meal arrives, G cells release gastrin-17 into the bloodstream; it travels to the stomach wall and triggers the secretion of hydrochloric acid needed for digestion. It is the predominant bioactive gastrin form in the antrum, accounting for approximately 80–90% of the total postprandial gastrin bioactivity (Zeng and colleagues 2020). The 16-residue sequence stored here is the core backbone; the biologically active hormone also carries a C-terminal amide group (–NH₂) on the terminal phenylalanine — a post-translational modification absent from the raw sequence but essential for high potency at the gastrin receptor (Zeng and colleagues 2020).

History

The existence of a gastric secretagogue hormone was first proposed by John Sydney Edkins in 1905, who found that extracts of the antral mucosa could stimulate acid secretion. The molecular identity of the hormone remained uncertain for decades. In 1964, Roderic Alfred Gregory and Hilda Tracy at the University of Liverpool purified and sequenced gastrin from porcine antral mucosa, identifying it as a 17-amino-acid peptide. George Kenner, also at Liverpool, contributed to its chemical synthesis and characterisation. These studies established the molecular basis of gastric acid control and launched the broader field of gut hormone biology. Gregory and Tracy also characterised the longer G-34 form ("big gastrin") predominant in the duodenum; "gastrin-17" or "little gastrin" became the name for this shorter antral variant (Zeng and colleagues 2020). The evolutionary antiquity of the gastrin/CCK peptide family was later illustrated by the identification of CCK- and gastrin-like peptides in cartilaginous fish, placing the lineage at least 350 million years back (Johnsen and colleagues 1997, PNAS).

What it does

Gastrin-17 is the body's principal hormonal signal for post-meal gastric acid production. It acts primarily by binding the cholecystokinin-2 receptor (CCK2R, also called the gastrin receptor or CCK-B receptor) on two cell types in the stomach lining: enterochromaffin-like (ECL) cells and parietal cells. When ECL cells are stimulated, they release histamine, which then drives adjacent acid-secreting parietal cells — this indirect ECL-cell route is the dominant pathway for postprandial acid secretion. Gastrin-17 can also act directly on parietal cells via CCK2R, generating an intracellular calcium signal rather than the cAMP signal used by histamine (Zeng and colleagues 2020). Beyond acid control, gastrin-17 exerts trophic effects on the gastric epithelium, particularly promoting ECL cell proliferation and overall mucosal maintenance. Exogenous gastrin-17 infusion in healthy volunteers also raised lower esophageal sphincter pressure at physiological dose levels through a mechanism independent of acid secretion.

Serum gastrin-17 levels rise markedly after eating and return toward baseline within approximately two hours. Helicobacter pylori infection selectively elevates both fasting and postprandial G-17 — but not G-34 — because the bacterium predominantly colonises the antrum (the main source of G-17) and disrupts the acid-feedback mechanism that normally limits gastrin release.

Evidence

• Human: Gastrin-17 has been extensively studied as an endogenous hormone and as a non-invasive serum biomarker. Postprandial G-17 measurement, combined with pepsinogen-I and anti-H. pylori antibodies, forms the basis of serological gastric atrophy screening panels (GastroPanel); low fasting G-17 indicates antral atrophy, while elevated G-17 with low pepsinogen-I indicates corpus atrophy. Multiple clinical studies have evaluated these combinations for risk stratification of early gastric cancer. The anti-gastrin-17 immunogen G17DT (Gastrimmune), which induces antibodies that neutralise circulating G-17, was assessed in Phase II studies in advanced gastric and pancreatic cancer; in the pancreatic cancer cohort, patients who mounted an antibody response showed greater survival than non-responders.
• Animal: Transgenic mice overexpressing progastrin (the G-17 precursor) showed increased predisposition to colonic neoplasia, establishing a causal link between sustained gastrin signalling and gastrointestinal carcinogenesis (Zeng and colleagues 2020). CCK2R-knockout mice display gastric mucosal phenotypes consistent with loss of trophic gastrin tone.
• In vitro: Gastrin/CCK2R signalling has been mapped across dozens of cell lines, with downstream networks involving MAPK, PI3K/AKT, PKC, and EGFR transactivation documented in detail (Zeng and colleagues 2020). Cryo-EM structures of CCK2R–Gq signalling complexes bound to gastrin-17 revealed the structural basis for the receptor's preference for gastrin over CCK, and showed that CCK2R couples primarily to Gq (Ding and colleagues, Cell Discovery 2022).

Known effects

• Gastric acid secretion — Principal physiological role; operates through ECL-cell histamine release and direct parietal cell stimulation via CCK2R (Zeng and colleagues 2020)
• Gastric mucosal trophic effects — ECL cell proliferation and epithelial maintenance; supported by animal knockout models and clinical hypergastrinaemia observations
• Lower esophageal sphincter tone — Increases lower esophageal sphincter pressure in humans at physiological doses via an acid-independent mechanism
• Serum biomarker for gastric atrophy — Fasting and postprandial G-17 levels serve as indirect indicators of antral G-cell mass and mucosal integrity
• ECL hyperplasia under chronic hypergastrinaemia — Prolonged G-17 elevation (e.g., from long-term proton pump inhibitor use or autoimmune atrophic gastritis) can drive ECL hyperplasia; gastric carcinoid formation is rare in humans even at sustained high levels

Safety signals

Gastrin-17 is an endogenous hormone; published safety signals relate to pathological excess rather than to the administered peptide.

Chronic hypergastrinaemia — from Zollinger-Ellison syndrome, atrophic gastritis, or long-term PPI use — produces ECL hyperplasia and, rarely, gastric carcinoid tumours. In human atrophic gastritis, sustained hypergastrinaemia typically leads to hyperplasia without malignant progression, though risk is not zero.

Gastrin and CCK2R are overexpressed in multiple adenocarcinomas (gastric, pancreatic, colorectal, esophageal), where autocrine/paracrine gastrin signalling has been implicated in proliferation and resistance to apoptosis (Zeng and colleagues 2020). Whether circulating G-17 is causal in cancer initiation or is merely co-expressed in tumour tissue remains under investigation.

The G17DT immunogen (Phase II clinical studies in gastric and pancreatic cancer) was generally well tolerated; significant adverse reactions including injection-site pain and abscess formation were reported in a small number of gastric cancer patients.

Regulatory status

• US / EU: Gastrin-17 itself is not approved as a therapeutic agent. As an endogenous hormone it is used as a research reagent and diagnostic reference standard.
• G17DT (Gastrimmune): Anti-gastrin-17 immunogen. Received FDA orphan drug designation for adenocarcinoma of the pancreas in 2002 and fast-track designation in combination with gemcitabine. Development by Aphton Corporation was not continued to approval.
• Diagnostic assays: Serum G-17 immunoassays are commercially available in several markets (particularly Europe and East Asia) as part of gastric cancer risk screening panels.
• Radiolabeled analogs: DOTA-conjugated minigastrin derivatives targeting CCK2R (e.g., for imaging and therapy of medullary thyroid carcinoma and other CCK2R-expressing tumours) are under Phase I clinical investigation. None have received regulatory approval (Roosenburg and colleagues 2011).
• WADA: Not listed; gastrin-17 is not a prohibited substance.

Mechanism

Gastrin-17 is produced by post-translational processing of the 101-residue precursor preprogastrin. The biologically active mature form is C-terminally amidated (–Phe-NH₂ at the C-terminus); this amidation is required for full agonist activity at CCK2R. Tyrosine sulfation occurs in a subset of G-17 molecules but has negligible effect on CCK2R binding affinity — in contrast to CCK1R, where sulfation of the equivalent tyrosine is required for high-affinity engagement. Sulfated and non-sulfated G-17 therefore bind CCK2R with comparable sub-nanomolar affinity (Zeng and colleagues 2020).

CCK2R is a class A GPCR that couples primarily to Gq, activating phospholipase C → inositol trisphosphate → intracellular calcium release → protein kinase C. Downstream consequences include MAPK/ERK activation, EGFR transactivation via MMP-mediated heparin-binding EGF release, and — in parietal cells — stimulation of the H⁺/K⁺-ATPase (proton pump). Cryo-EM structures of CCK1R–Gs and CCK2R–Gq complexes demonstrated that CCK2R can also engage Gs in some cellular contexts, and revealed how five residues in the second extracellular loop of CCK2R create a binding pocket that accommodates the C-terminal tetrapeptide common to gastrin and CCK without requiring the sulfated tyrosine that CCK1R demands — providing the structural explanation for gastrin's selectivity for CCK2R over CCK1R (Ding and colleagues 2022).

In ECL cells, CCK2R activation induces histidine decarboxylase expression and calcium-dependent histamine release. This histamine acts on H2 receptors on parietal cells, elevating cAMP and activating the proton pump — the dominant route for meal-stimulated acid production. Direct parietal cell stimulation by gastrin-17 through CCK2R operates via a calcium-based mechanism distinct from the histamine/cAMP pathway (Zeng and colleagues 2020).

Trophic effects on the gastric mucosa involve mTOR-mediated protein synthesis, cyclin D1 transcription, and PI3K/AKT-mediated suppression of apoptosis. Sustained hypergastrinaemia amplifies these proliferative signals in ECL cells, accounting for the hyperplasia and occasional carcinoid tumour formation observed in chronic hypergastrinaemic states.

Related peptides

• Gastrin-34 (Big Gastrin) — the 34-residue gastrin form, predominant in the duodenum; shares the same C-terminal active tetrapeptide as G-17 and activates CCK2R with comparable potency, but with a longer circulating half-life. Postprandial levels change less markedly than G-17. Not yet assigned a separate platform card.
• CCK-8 — the biologically active C-terminal octapeptide of cholecystokinin; shares the C-terminal pentapeptide with gastrin but binds CCK1R with 500–1,000-fold higher affinity than G-17 (Zeng and colleagues 2020). Not yet assigned a separate platform card.
• Minigastrin analogs — synthetic truncated gastrin derivatives (e.g., DOTA-MGS5) developed for CCK2R-targeted radionuclide imaging and therapy of neuroendocrine tumours; structurally derived from G-17's C-terminal active region (Roosenburg and colleagues 2011).