Duodenal substance

Duodenal Substance

Duodenal substance is a historical and contemporary term encompassing the biologically active secretions and tissue-derived extracts of the duodenal mucosa. In pharmacological and supplement contexts, the term most precisely refers to preparations—crude or refined—of the duodenal lining or its principal hormonal product, secretin, which was identified from this tissue. As a dietary supplement, "duodenal substance" appears most commonly within the tradition of glandular therapy, where freeze-dried or lyophilized duodenal tissue is orally administered. In clinical medicine, the active principle, secretin, is used diagnostically and, historically, therapeutically, always by parenteral injection rather than oral ingestion.

Identity: Nomenclature, Source, and Forms

Botanical and Chemical Names

"Duodenal substance" is not a single chemical entity but a category of preparations. The primary identified active principal is secretin, a peptide hormone whose systematic chemical identity has been established. Secretin is a 27-amino acid linear peptide hormone produced by enteroendocrine S cells of the duodenal and proximal jejunal mucosa. Human secretin is synthesized as a pre-propeptide of 121 amino acid residues, containing a signal peptide, propeptide, and the secretin sequence itself; this pre-propeptide is cleaved from both ends to achieve the active peptide of 27 amino acid residues. In humans, the secretin peptide is encoded by the SCT gene.

In older literature—particularly pre-1920 biomedical writing—"the secretin of Bayliss and Starling," "acid extract of duodenal mucous membrane," and the proprietary preparation "Antiglucosine" were all used as synonyms or closely related preparations. The preparation described as "Antiglucosine" is an acid extract of duodenal mucous membrane, and differs from a solution of secretin in being made freshly every other day.

Natural Sources

Secretin is predominantly synthesized by the S-cells in the crypts of Lieberkühn of the duodenal epithelium. It is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. In supplement manufacturing, most glandular products are from a bovine source, since it is easier to collect tissue from larger animals. Pharmaceutical-grade secretin has also been derived from porcine (pig) duodenal mucosa, and a fully synthetic human sequence is now available. Secretin used pharmaceutically is prepared from the duodenal mucosa of pigs.

Common Forms and Preparations

Duodenal substance appears in commerce in the following forms:

• Freeze-dried (lyophilized) glandular powder: Bovine duodenal tissue that has been freeze-dried and encapsulated. This is the form most common in the dietary supplement market under glandular therapy frameworks.
• Acid extracts of duodenal mucosa: The earliest pharmaceutical preparation, produced by scraping mucosal tissue, grinding it with sand in weak hydrochloric acid, and filtering the resulting solution for injection. This was the original experimental preparation of Bayliss and Starling.
• Porcine-derived injectable secretin: A purified extract formerly widely used in clinical diagnostics, now largely replaced by the synthetic form.
• Synthetic human secretin: A recombinant, sequence-identical synthetic peptide (commercially available under the brand name SecreFlo), used in parenteral diagnostic procedures. This is the pharmaceutical standard.

Two dosage forms have been available for secretin used as a medicine: it is either placed under the tongue or given intravenously.

Traditional and Historical Use

Ancient and Pre-Scientific Traditions: Glandular Eating

The broader tradition underlying duodenal substance as a supplement is organotherapy—the use of animal organs as food or medicine. Animal glands have been valued as food and as medicine for millennia. In the late 1800s, treatment with thyroid extract caused dramatic improvement in patients with myxedema. Shortly thereafter, multiple other glandular extracts became available, both individually and in combinations, but their use gradually fell into disfavor, partly due to overpromotion by the manufacturers.

Early Scientific-Era Use: 1902–1910

The specific medical application of duodenal substance is inseparable from the landmark discovery of secretin. In collaboration with physiologist W. M. Bayliss, English physician E. H. Starling discovered secretin in 1902. In 1902, Bayliss and Starling were studying how the nervous system controls the process of digestion; it was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered—by cutting all the nerves to the pancreas in their experimental animals—that this process was not governed by the nervous system, and determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion secretin.

The experimental procedure that produced the first crude "duodenal substance" used therapeutically was described in vivid contemporary accounts: Bayliss and Starling scraped some mucosa from the duodenum, added acid to it, ground it up with sand, filtered it, and injected it intravenously into an anesthetized dog—pancreatic secretion followed a few seconds later. This type of "chemical messenger" substance is now called a hormone, a term coined by Starling in 1905.

Within years of this discovery, physicians attempted therapeutic use of duodenal extracts. Dr. John Hill Abram reported a therapeutic experiment—the use of an acid extract of the duodenal mucous membrane in the treatment of diabetes mellitus. The procedure was based on the work of Bayliss and Starling, who had shown that the contact of hydrochloric acid with the duodenal epithelium causes in the latter the production of a substance which stimulates the pancreas to secretion. With this increased activity of the pancreas there was an added flow of lymph in the vessels passing from the gland, and it was thus anticipated—though not proved—that there is an increase in the internal secretion of the pancreas; since the pancreas plays an important part in the assimilation of carbohydrates, an agent which stimulates its activity might reasonably be expected to exert some influence in cases of diabetes.

Bayliss and Starling demonstrated that when hydrochloric acid comes into contact with the epithelial cells of the duodenum and upper part of the jejunum, a substance is found therein to which they gave the name secretin; this substance is carried by the blood stream to the pancreas, on the external secretion of which gland it acts as a specific stimulant; the secretin is only formed in health when free hydrochloric acid is passing along the duodenum, which only occurs in the presence of food.

Early clinical use of duodenal extracts as treatment for diabetes mellitus was attempted in the first decade of the twentieth century, well before the isolation of insulin. However, the results were inconsistent. Solutions of secretin were known to become inert on keeping, and early practitioners noted that negative results may have been due to instability of the preparation; the treatment was at times discontinued because the solution was liable to undergo decomposition on very hot days.

Glandular Therapy in the Twentieth Century

The history of the use of thyroid, pancreatic, adrenal, thymus, and liver extracts suggests that glandular extracts can be beneficial, especially when potential mechanisms of action and methods of preparation are considered. Duodenal glandular preparations became one item in the broader catalogue of organotherapy supplements. In this tradition, duodenal tissue was used primarily as a digestive aid and mucosal support agent. Contemporary supplement labeling in this tradition has described duodenal glandular as enhancing digestion, healing and protecting the digestive tract from ulcers, and enhancing absorption of vitamin B12—though these claims are not substantiated by controlled human clinical trials.

Key Constituents and Active Compounds

Secretin

Secretin helps regulate the pH of the duodenum by inhibiting the secretion of gastric acid from the parietal cells of the stomach and stimulating the production of bicarbonate from the ductal cells of the pancreas. Secretin also increases water and bicarbonate secretion from duodenal Brunner's glands to buffer the incoming protons of the acidic chyme, and reduces acid secretion by parietal cells of the stomach through at least three mechanisms: by stimulating release of somatostatin, by inhibiting release of gastrin in the pyloric antrum, and by direct downregulation of the parietal cell acid secretory mechanics.

Secretin counteracts blood glucose concentration spikes by triggering increased insulin release from the pancreas following oral glucose intake, and modulates water and electrolyte transport in pancreatic duct cells, liver cholangiocytes, and epididymis epithelial cells.

Secretin also stimulates the secretion of bicarbonate and water by cholangiocytes in the bile duct, protecting it from bile acids by controlling the pH and promoting the flow in the duct.

In 2007, secretin was discovered to play a role in osmoregulation by acting on the hypothalamus, pituitary gland, and kidney.

Cholecystokinin (CCK) and Other Duodenal Hormones

Crude duodenal substance preparations necessarily contain not only secretin but the full array of duodenal mucosal hormones and peptides, most notably cholecystokinin. Cholecystokinin (CCK) is a gastrointestinal hormone secreted from the duodenal mucosal cells by ingestion of lipid, protein, or other nutrients; this hormone is known to accelerate enzyme secretion from the pancreas, to contract the gallbladder, and to delay the transfer of gastric contents to the duodenum by closing the pylorus of the stomach. CCK also directly acts on the central nervous system to suppress appetite, having the physiological function of inducing a feeling of fullness.

The crude extract that Bayliss and Starling used in their original experiment caused the pancreas to secrete enzymes as well as water and bicarbonates; because purified secretin seemed to stimulate only the output of water and bicarbonate, researchers began to look for the material in the extract that stimulated secretion of the enzymes. Secretin and cholecystokinin (CCK) work together to manage digestion.

Other Constituents of Glandular Preparations

Beyond the hormonal content, glandular products of duodenal origin contain structural peptides, enzymes, and other tissue components native to the intestinal mucosa. Glandulars contain nutritional peptides, enzymes, and substances believed to be hormone precursors; however, it is unclear precisely how these substances may affect energy levels, health, and/or mental function. The mucosal lining of the duodenum is also rich in Brunner's gland secretions, mucins, immunoglobulins (particularly secretory IgA), and digestive enzyme precursors—all present in tissue-derived extracts to varying degrees depending on preparation method.

Mechanism of Secretin Release in Vivo

Secretin is secreted in response to acidification of the duodenum, which occurs most commonly when liquified ingesta from the stomach are released. Many materials other than hydrochloric acid stimulate the release of secretin by the duodenal mucosa; water, alcohol, fatty acids, partially hydrolyzed protein, and certain amino acids are all effective. The receptor through which secretin acts is well characterized: the secretin receptor has seven membrane-spanning domains and characteristics typical of a G protein-coupled receptor.

Scientific Evidence by Area of Use

1. Digestive and Pancreatic Function (Established Physiology)

The role of duodenal-derived secretin in regulating pancreatic and biliary secretion is established physiological fact, not a supplement claim. Human secretin is a synthetic peptide hormone produced by cells in the duodenum in response to acidification; it stimulates pancreatic ductal cells to secrete pancreas fluid in large volumes that contain bicarbonate; it may also work through vagal-vagal neural pathways since stimulation of the efferent vagus nerve stimulates bicarbonate secretion. Secretin primarily functions to neutralize the pH in the duodenum, allowing digestive enzymes from the pancreas—such as pancreatic amylase and pancreatic lipase—to function optimally.

Evidence strength: Extremely strong for endogenous physiology. These mechanisms were established by classical physiological experimentation beginning in 1902 and have been repeatedly confirmed. There is no controlled clinical evidence that oral duodenal glandular supplements exert measurable pharmacological effects through these mechanisms in humans (see Bioavailability Limitations below).

2. Diagnostic Use: Pancreatic Exocrine Dysfunction

Secretin administered parenterally has an established diagnostic role. Stimulation of pancreatic secretions, including bicarbonate, by secretin aids in the diagnosis of pancreatic exocrine dysfunction. Stimulation of pancreatic secretions also facilitates identification of the ampulla of Vater and accessory papilla during endoscopic retrograde cholangiopancreatography (ERCP).

Evidence strength: Well-established in clinical gastroenterology practice. This use is restricted to parenteral (injectable) secretin, not oral glandular supplements.

3. Diagnostic Use: Zollinger–Ellison Syndrome

Intravenous secretin is used in the secretin stimulation test for the diagnosis of Zollinger–Ellison syndrome (ZES), a condition caused by gastrin-secreting tumors. Secretin inhibits gastrin release in normal subjects but, on the contrary, stimulates gastrin secretion in Zollinger–Ellison syndrome patients; the secretin provocation test has been reported to have high sensitivity (80–94%) and specificity (81–100%) for Zollinger–Ellison syndrome. The standard dosing protocol used in clinical studies has been reported as follows: the secretin stimulation test involves rapid intravenous infusion of 2 units/kg secretin over approximately one minute. An independent dose-comparison study found that the 0.26 microg/kg secretin stimulation test has the best diagnostic efficacy for ZES, and that higher gastrin increases after 0.78 microg/kg compared to 0.26 microg/kg secretin contributed to a slightly more sensitive (82.9% vs. 80.5%) but less specific (68.8% vs. 81.3%) test.

Evidence strength: Strong for parenteral use in a supervised clinical setting. Not applicable to oral supplementation.

4. Diabetes Mellitus (Historical; No Current Evidence)

As noted above, the earliest therapeutic application of acid extracts of duodenal mucosa was the attempt to treat diabetes mellitus in 1905–1906. These were anecdotal case reports conducted before the discovery of insulin, based on the hypothesis that stimulating the pancreas might increase its internal secretion. It was recognized that in different cases there may well be disturbances in different parts of the carbohydrate-assimilation mechanism, and thus it was not improbable that a remedy which succeeds in some cases may altogether fail in others. These historical attempts involved injected preparations. No modern controlled clinical trials have investigated oral duodenal substance for diabetes.

Evidence strength: Anecdotal case reports only, from 1905–1906; pre-insulin era; not applicable to contemporary practice or supplementation.

5. Autism Spectrum Disorder (Thoroughly Investigated; Negative Findings)

Beginning in the late 1990s, case reports suggested that intravenous secretin might improve symptoms of autism spectrum disorder (ASD), generating significant public and clinical interest. This led to an extensive programme of randomized controlled trials. Manuscripts published based on non-controlled case reports suggested that intravenous therapy with secretin was a useful treatment for autism spectrum disorder; these reports generated a great deal of interest from parents of autistic children and autism support groups.

The subsequent evidence base is now large and consistently negative. A Cochrane systematic review included 16 randomised trials with a placebo control group, with over 900 children involved; the review found no evidence that single or multiple dose intravenous secretin is effective in improving the main problems seen in ASD, namely a lack of social interaction and communication and restrictive, repetitive behaviours and routines, and as such it should not currently be recommended or administered as a treatment for ASD.

Participant numbers in the treatment arms of the randomized controlled trials ranged from 21 to 47 subjects; no studies revealed significantly greater improvements in measures of language, cognition, or autistic symptoms when compared with placebo; study authors who reported improvement over time did so equally for both intervention and placebo groups; there was also no benefit demonstrated according to type of secretin (porcine or synthetic); overall, the studies uniformly point to a lack of significant impact of secretin in the treatment of autism symptoms—a conclusion confirmed by a Cochrane review of 13 randomized studies showing clear evidence that secretin lacks benefit for treating children with ASDs.

Further experimental assessment of secretin's effectiveness for ASD can only be justified if there is convincing new evidence that secretin can influence brain function in a way that could benefit children with ASD or a link is proven between secretin and the known cause of ASD.

Evidence strength: High-quality evidence (multiple RCTs, Cochrane meta-analysis) consistently shows no benefit for ASD. The question is thoroughly investigated and effectively closed.

6. Obesity, Satiety, and Brown Adipose Tissue Activation (Emerging; Preliminary Human Data)

A newer and scientifically active area of investigation concerns secretin's role in energy homeostasis—specifically, its ability to activate brown adipose tissue (BAT) and induce satiation. Apart from the well-established exocrine functions of secretin, it also has a mild incretin effect, induces appetite suppression and brown adipose tissue (BAT) activation, and during prolonged fasting it enhances lipolysis.

When endogenous secretin was neutralized by an antibody in animal studies, meal size and duration were significantly increased compared to controls; these results confirmed that the satiation effect is induced by secretin and BAT thermogenesis.

In human studies, secretin increased subjective satiety compared to placebo in fasting conditions and during early feeding, but this effect was no longer significant in the postprandial evaluation. A placebo-controlled PET-fMRI study in humans reported: the study used brain metabolic and BOLD measures to dissect the modulatory effects of secretin on brain functions associated with satiation; findings showed that secretin modulates caudate glucose metabolism via the BAT-brain axis, enhances BOLD response in inhibitory control, and reduces reward-related BOLD response; further evidence showed these measured effects are tightly linked via secretin-mediated brain neurometabolic coupling; the study highlights the potential role of secretin in treating eating disorders and obesity.

Secretin's BAT activation and satiation effects were shown to translate to humans; these results highlight that secretin has a rare dual role on energy homeostasis, potentially both increasing energy expenditure and decreasing energy intake.

The investigation of potential effects of secretin in hedonic-driven food intake, bariatric surgery, and chronic treatment using suitable application strategies to overcome pharmacokinetic limitations will provide further insight into its potential to influence energy balance.

Evidence strength: Preliminary and emerging. Mechanistic studies in mice and small human imaging studies support the hypothesis, but there are no large-scale or long-term RCTs establishing secretin as an effective weight-management intervention. All human studies have used parenteral (intravenous) delivery, not oral supplements.

7. Peptic and Duodenal Ulcers (Historical; No Controlled Clinical Evidence for Supplementation)

Secretin is sometimes used to treat peptic ulcers. This use, when it occurs, is by parenteral administration based on secretin's known ability to inhibit gastric acid secretion. There are no peer-reviewed, controlled clinical trials demonstrating that oral duodenal glandular supplements treat or prevent duodenal ulcers in humans.

Evidence strength: No high-quality clinical evidence for oral supplementation. Mechanistic plausibility exists for parenterally delivered secretin, but this does not translate to the supplement context.

Body Systems and Health Areas Associated with Duodenal Substance

• Gastrointestinal system: The primary domain. Secretin and duodenal-derived hormones regulate acid–base balance in the duodenum, stimulate pancreatic bicarbonate and water secretion, modulate gastric motility, and protect the mucosal lining. Secretin helps regulate the pH of the duodenum by inhibiting gastric acid secretion from parietal cells of the stomach and stimulating production of bicarbonate from pancreatic ductal cells.
• Pancreas: Secretin targets the pancreas; pancreatic centroacinar cells have secretin receptors in their plasma membrane.
• Hepatobiliary system: Secretin stimulates the secretion of bicarbonate and water by cholangiocytes in the bile duct, protecting it from bile acids by controlling pH and promoting flow in the duct.
• Metabolic/endocrine system: Secretin counteracts blood glucose concentration spikes by triggering increased insulin release from the pancreas following oral glucose intake.
• Renal/hypothalamic (osmoregulation): In 2007, secretin was discovered to play a role in osmoregulation by acting on the hypothalamus, pituitary gland, and kidney.
• Central nervous system / appetite regulation: Emerging evidence, as detailed above, identifies a gut–BAT–brain axis through which secretin influences satiety signalling and food reward processing.

Dosage Forms and Dosages Reported in Studies

Because the pharmacologically active principle (secretin) is a peptide that is degraded in the gastrointestinal tract when taken orally, all dosages reported in peer-reviewed clinical studies refer to parenteral (intravenous) administration. No peer-reviewed clinical dose-ranging studies for oral duodenal glandular supplements have been identified in the authoritative literature searched for this article.

Parenteral Secretin: Dosages from Clinical Studies

• Zollinger–Ellison syndrome diagnosis: The secretin stimulation test involves rapid intravenous infusion of 2 units/kg secretin over approximately one minute. A comparative dosing study reported: intra-individual comparison using both 0.26 microg/kg and 0.78 microg/kg secretin performed in 13 ZES patients and 12 controls was analyzed.
• Autism spectrum disorder trials: In an open-label trial, subjects received one injection of secretin at 2 IU/kg.
• Pancreatic exocrine function testing: Secretin stimulates pancreatic secretions, including bicarbonate, to aid in the diagnosis of pancreatic exocrine dysfunction by intravenous bolus administration; the specific dose varies by protocol and manufacturer.

Oral Bioavailability: A Critical Limitation

A fundamental pharmacological limitation applies to all oral preparations of duodenal substance containing secretin or other peptide hormones: peptides face profound barriers to oral bioavailability. Oral administration of peptides and proteins is often limited by inherent biopharmaceutical limitations such as limited solubility in the intestinal environment, short half-life, high molecular weight, hydrophilicity, susceptibility to enzymatic degradation, low permeability across the intestinal epithelium, and low stability in the gastrointestinal tract—all of which ultimately lead to poor oral bioavailability. Peptide and protein therapeutics are highly specific and potent biomolecules, but their oral delivery is significantly hindered by enzymatic degradation, instability, and poor permeability through the gastrointestinal epithelium, resulting in low bioavailability.

This is a central scientific concern for oral duodenal glandular supplements: the secretin and other peptide hormones they contain would be expected to be digested in the stomach and upper intestine rather than absorbed intact and delivered to target receptors. No published peer-reviewed human studies have measured bioavailability of intact secretin or other duodenal peptide hormones from oral glandular supplements.

Safety Considerations and Interactions

Allergic and Anaphylactic Reactions (Parenteral Use)

Although allergic reactions were a concern with porcine-derived secretin products, no allergic reactions were observed after test dose or full dose of the synthetic human secretin product (SecreFlo) in clinical trials; nevertheless, the prescribing information recommends having resuscitation equipment available. Porcine secretin carries a higher risk of anaphylactoid reactions due to potential immunogenicity of the non-human peptide. These risks pertain to injectable preparations used in clinical settings, not oral glandular supplements.

Drug Interactions (Parenteral Secretin)

Anticholinergic agents may blunt the pancreatic response to secretin, potentially causing false-negative results on pancreatic function testing; conversely, proton pump inhibitors and H2 receptor antagonists can elevate baseline gastrin levels, potentially causing false-positive results on the secretin stimulation test for gastrinoma; PPIs should be stopped at least one to two weeks (ideally two weeks) and H2 blockers at least 48–72 hours before secretin-based diagnostic testing. Additionally, anticholinergic agents may diminish the therapeutic effect of secretin.

Bovine Spongiform Encephalopathy (BSE) and Prion Risk

For glandular supplements derived from bovine tissue, a documented safety concern relates to prion contamination. It is critically important to use good-quality materials to avoid the prions that cause bovine spongiform encephalopathy (BSE); even before the advent of BSE, Australia and New Zealand had strict restrictions on the importation of animals and animal products, and no cases of BSE have occurred in these countries. Supplement purchasers and manufacturers should therefore verify the country of origin of bovine-source glandular products as a quality and safety consideration.

Stability

Even in its pharmaceutical form, secretin is not a stable molecule under all conditions. Early-twentieth-century clinical experience noted this problem, and it remains relevant: solutions of secretin are known to become inert on keeping, and it was thought that negative results in early clinical trials might have been due to the fact that the solution had been kept too long. Modern freeze-dried glandular products are subject to similar quality-control issues regarding maintenance of bioactive constituents.

Lack of Evidence for Oral Efficacy and Standardization

There are no established regulatory standards for duodenal glandular dietary supplements in terms of potency, purity, or defined clinical indications. Diseases associated with excessive or deficient secretion of secretin are not recognized as established clinical entities, which further limits the ability to define appropriate supplementation targets. The absence of controlled human data on oral preparations means the benefit–risk profile for duodenal substance as an oral supplement is uncharacterized by peer-reviewed clinical science.

Summary of Evidence Quality

The evidence landscape for "duodenal substance" separates sharply into two domains:

• Endogenous physiology of secretin and related duodenal hormones: Exceptionally well-established by over a century of basic and clinical research. The mechanisms by which the duodenum and its hormonal secretions regulate digestion, gastric acid, pancreatic function, and hepatobiliary physiology are among the best-characterized in gastrointestinal medicine.
• Oral supplementation with duodenal glandular preparations: No peer-reviewed, controlled human clinical trials. The mechanistic basis for benefit via oral peptide absorption is highly questionable given the documented barriers to oral peptide bioavailability. Claims made in supplement marketing for oral duodenal products lack scientific substantiation from the types of sources reviewed for this article.
• Injectable (pharmaceutical) secretin: Well-evidenced for diagnostic use in pancreatic exocrine dysfunction and Zollinger–Ellison syndrome; definitively shown to be ineffective for autism spectrum disorder across 16+ RCTs and a Cochrane systematic review; emerging preliminary evidence for satiety modulation and BAT activation with promising but early-stage human data.

References

• StatPearls / NIH: Physiology, Secretin
• Wikipedia: Secretin (referenced for established scientific facts)
• PMC: Acid Extract of the Duodenal Mucous Membrane as a Remedy in Diabetes Mellitus (1906)
• PMC: On the Treatment of Diabetes with Secretin (1906)
• PMC: Secretin (1908, historical)
• PMC: Secretin and the exposition of hormonal control
• Journal of Endocrinology: Ernest Starling and 'Hormones': an historical commentary (2005)
• Hektoen International: Ernest Henry Starling and the birth of English Physiology
• Pancreapedia: Secretin
• Cochrane: Intravenous secretin for autism spectrum disorders (ASD)
• PMC: Intravenous secretin for autism spectrum disorders (ASD) – full Cochrane review text
• PMC: A Systematic Review of Secretin for Children With Autism Spectrum Disorders
• NIH/DARE: Secretin as a treatment for autism: a review of the evidence
• PMC: In children with autism, is intravenous secretin more effective than placebo?
• PMC: Pleiotropic Effects of Secretin: A Potential Drug Candidate in the Treatment of Obesity?
• Frontiers in Endocrinology: Pleiotropic Effects of Secretin (Laurila et al., 2021)
• PMC: Secretin modulates appetite via brown adipose tissue-brain axis
• Endocrinology (Oxford): Secretin as a Satiation Whisperer With the Potential to Turn into an Obesity-curbing Knight
• Drugs.com Professional: Secretin (mechanism, clinical uses, interactions)
• PeptideInsight: Secretin – Research Evidence and Safety Profile
• PMC: A Brief History of Glandular Therapy: More Than Just Thyroid
• PMC: Barriers and Strategies for Oral Peptide and Protein Therapeutics Delivery
• ScienceDirect: Zollinger–Ellison Syndrome – overview including secretin stimulation test
• PubMed: Diagnostic efficacy of the secretin stimulation test for Zollinger–Ellison syndrome (Kuiper et al., 2010)
• Annals of Internal Medicine: Secretin and Calcium Provocative Tests in the Zollinger–Ellison Syndrome
• Colorado State University Hypertexts for Biomedical Sciences: Secretin
• EBSCO Research Starters: Bayliss and Starling Establish the Role of Hormones