World Library  
Flag as Inappropriate
Email this Article

Secretin

Article Id: WHEBN0000222183
Reproduction Date:

Title: Secretin  
Author: World Heritage Encyclopedia
Language: English
Subject: Somatostatin, Gastrin, Gastrointestinal physiology, Digestive enzyme, Cholecystokinin
Collection: Autism, Digestive System, Intestinal Hormones, Peptide Hormones
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Secretin

Secretin
Identifiers
Symbol
External IDs GeneCards:
Orthologs
Species Human Mouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)
RefSeq (protein)
Location (UCSC)
PubMed search

Secretin is a peptide hormone that regulates water homeostasis throughout the body, and influences the environment of the duodenum by regulating secretions in the stomach and pancreas. Secretin is produced in the S cells of the duodenum, which are located in the intestinal glands.[1] In humans, the secretin peptide is encoded by the SCT gene.[2] Secretin was the first hormone to be identified.[3]

Secretin also 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 centroacinar cells and intercalated ducts of the pancreas.[4]

In 2007, secretin was discovered to play a role in osmoregulation by acting on the hypothalamus, pituitary, and kidney.[5][6]

Contents

  • Discovery 1
  • Structure 2
  • Physiology 3
    • Production 3.1
    • Stimulus 3.2
    • Function 3.3
  • Uses 4
  • Osmoregulation 5
  • Food intake 6
  • See also 7
  • References 8
  • Further reading 9
  • External links 10

Discovery

In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion.[7] 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, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion secretin. Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.

Structure

Secretin is initially synthesized as a 120 amino acid precursor protein known as prosecretin. This precursor contains an N-terminal signal peptide, spacer, secretin itself (residues 28–54), and a 72-amino acid C-terminal peptide.[2]

The mature secretin peptide is a linear peptide hormone, which is composed of 27 amino acids and has a molecular weight of 3055. A helix is formed in the amino acids between positions 5 and 13. The amino acids sequences of secretin have some similarities to that of glucagon, vasoactive intestinal peptide (VIP), and gastric inhibitory peptide (GIP). Fourteen of 27 amino acids of secretin reside in the same positions as in glucagon, 7 the same as in VIP, and 10 the same as in GIP.[8]

Secretin also has an amidated carboxyl-terminal amino acid which is valine.[9] The sequence of amino acids in secretin is H–His-Ser-Asp-Gly-Thr-Phe-Thr-Ser-Glu-Leu-Ser-Arg-Leu-Arg-Asp-Ser-Ala-Arg-Leu-Gln-Arg-Leu-Leu-Gln-Gly-Leu-Val–NH2.[9]

Physiology

Production

Secretin is synthesized in cytoplasmic secretory granules of S-cells, which are found mainly in the mucosa of the duodenum, and in smaller numbers in the jejunum of the small intestine.[10]

Stimulus

Secretin is released into circulation and/or intestinal lumen in response to low duodenal pH that ranges between 2 and 4.5 depending on species.[11] Also, the secretion of secretin is increased by the products of protein digestion bathing the mucosa of the upper small intestine.[12]

The acidity is due to intestine. Bicarbonate is a base that neutralizes the acid, thus establishing a pH favorable to the action of other digestive enzymes in the small intestine and preventing acid burns.[13] Other factors are involved in the release of secretin such as bile salts and fatty acids, which result in additional bicarbonates being added to the small intestine.[14] Secretin release is inhibited by H2 antagonists, which reduce gastric acid secretion. As a result, if the pH in the duodenum increases above 4.5, secretin cannot be released.[15]

Function

Secretin stimulates the release of a watery bicarbonate solution from the pancreatic and bile duct epithelium. Pancreatic centroacinar cells have secretin receptors in their plasma membrane. As secretin binds to these receptors, it stimulates adenylate cyclase activity and converts ATP to cyclic AMP.[16] Cyclic AMP acts as second messenger in intracellular signal transduction and leads to an increase in the release of watery bicarbonate. It is known to promote the normal growth and maintenance of the pancreas.

Secretin increases water and bicarbonate secretion from duodenal Brunner's glands to buffer the incoming protons of the acidic chyme.[17] It also enhances the effects of cholecystokinin to induce the secretion of digestive enzymes and bile from pancreas and gallbladder, respectively.

It counteracts blood glucose concentration spikes by triggering increased insulin release from pancreas, following oral glucose intake.[18]

Although secretin releases gastrin from gastrinomas, it inhibits gastrin release from the normal stomach. It reduces acid secretion by parietal cells of the stomach.[19]:844 It does this through at least three mechanisms: 1) By stimulating release of somatostatin, 2) By inhibiting release of gastrin in the pyloric antrum, and 3) By direct downregulation of the parietal cell acid secretory mechanics.[20] This helps neutralize the pH of the digestive products entering the duodenum from the stomach, as digestive enzymes from the pancreas (e.g., pancreatic amylase and pancreatic lipase) function optimally at slightly basic pH.[17]

In addition, secretin stimulates pepsinogen secretion from chief cells, which can help break down proteins in food digestion. It stimulates release of glucagon, pancreatic polypeptide and somatostatin.[11]

Uses

Secretin has been widely used in medical field especially in pancreatic functioning test because it increases pancreatic secretions. Secretin is either injected[21] or given through a tube that is inserted through nose, stomach then duodenum.[22] This test can provide information about whether there are any abnormalities in the pancreas which can include gastrinoma, pancreatitis or pancreatic cancer.

Secretin has been proposed as a possible treatment for autism based on a hypothetical gut-brain connection; as yet there is no evidence to support it as effective.[23][24]

Osmoregulation

Secretin modulates water and electrolyte transport in pancreatic duct cells,[25] liver cholangiocytes,[26] and epididymis epithelial cells.[27] It is found[28] to play a role in the vasopressin-independent regulation of renal water reabsorption.[5]

Secretin is found in the magnocellular neurons of the paraventricular and supraoptic nuclei of the hypothalamus and along the neurohypophysial tract to neurohypophysis. During increased osmolality, it is released from the posterior pituitary. In the hypothalamus, it activates vasopressin release.[6] It is also needed to carry out the central effects of angiotensin II. In the absence of secretin or its receptor in the gene knockout animals, central injection of angiotensin II was unable to stimulate water intake and vasopressin release.[29]

It has been suggested that abnormalities in such secretin release could explain the abnormalities underlying type D syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH).[6] In these individuals, vasopressin release and response are normal, although abnormal renal expression, translocation of aquaporin 2, or both are found.[6] It has been suggested that "Secretin as a neurosecretory hormone from the posterior pituitary, therefore, could be the long-sought vasopressin independent mechanism to solve the riddle that has puzzled clinicians and physiologists for decades."[6]

Food intake

Secretin and its receptor are found in discrete nuclei of the hypothalamus, including the paraventricular nucleus and the arcuate nucleus, which are the primary brain sites for regulating body energy homeostasis. It was found that both central and peripheral injection of Sct reduce food intake in mouse, indicating an anorectic role of the peptide. This function of the peptide is mediated by the central melanocortin system.[30]

See also

References

  1. ^ Häcki WH (September 1980). "Secretin". Clin Gastroenterol 9 (3): 609–32.  
  2. ^ a b Kopin AS, Wheeler MB, Leiter AB (March 1990). "Secretin: structure of the precursor and tissue distribution of the mRNA". Proc. Natl. Acad. Sci. U.S.A. 87 (6): 2299–2303.  
  3. ^ http://www.ncbi.nlm.nih.gov/pubmed/11816326
  4. ^ Whitmore TE, Holloway JL, Lofton-Day CE, Maurer MF, Chen L, Quinton TJ, Vincent JB, Scherer SW, Lok S (2000). "Human secretin (SCT): gene structure, chromosome location, and distribution of mRNA". Cytogenet. Cell Genet. 90 (1–2): 47–52.  
  5. ^ a b Chu JY, Chung SC, Lam AK, Tam S, Chung SK, Chow BK (April 2007). "Phenotypes developed in secretin receptor-null mice indicated a role for secretin in regulating renal water reabsorption". Mol. Cell. Biol. 27 (7): 2499–2511.  
  6. ^ a b c d e Chu JY, Lee LT, Lai CH, Vaudry H, Chan YS, Yung WH, Chow BK (September 2009). "Secretin as a neurohypophysial factor regulating body water homeostasis". Proc. Natl. Acad. Sci. U.S.A. 106 (37): 15961–15966.  
  7. ^ Bayliss W, Starling EH (Sep 12, 1902). "The mechanism of pancreatic secretion" (PDF). J. Physiol. (London) 28 (5): 325–353.  
  8. ^ Williams, Robert L. (1981). Textbook of Endocrinology. Philadelphia: Saunders. p. 697.  
  9. ^ a b DeGroot, Leslie Jacob (1989). J. E. McGuigan, ed. Endocrinology. Philadelphia: Saunders. p. 2748.  
  10. ^ Polak JM, Coulling I, Bloom S, Pearse AG (1971). "Immunofluorescent localization of secretin and enteroglucagon in human intestinal mucosa". Scandinavian Journal of Gastroenterology 6 (8): 739–744.  
  11. ^ a b Frohman, Lawrence A.; Felig, Philip (2001). "Gastrointestinal Hormones and Carcinoid Syndrome". In P. K. Ghosh and T. M. O’Dorisio. Endocrinology & metabolism. New York: McGraw-Hill, Medical Pub. Div. p. 1326.  
  12. ^ William F. Ganong, MD (2003). "26. Regulation of Gastrointestinal Function". Review of Medical Physiology (Twenty-First ed.). New York: McGraw-Hill, Medical Pub. Div.  
  13. ^ http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/secretin.html
  14. ^ Osnes M, Hanssen LE, Flaten O, Myren J (March 1978). "Exocrine pancreatic secretion and immunoreactive secretin (IRS) release after intraduodenal instillation of bile in man". Gut 19 (3): 180–184.  
  15. ^ Rominger JM, Chey WY, Chang TM (July 1981). "Plasma secretin concentrations and gastric pH in healthy subjects and patients with digestive diseases". Digestive diseases and sciences 26 (7): 591–597.  
  16. ^ Gardner JD (1978). "Receptors and gastrointestinal hormones". In Sleisenger MH, Fordtran JS. Gastrointestinal Disease (2nd ed.). Philadelphia: WB Saunders Company. 
  17. ^ a b Hall, John E.; Guyton, Arthur C. (2006). Textbook of medical physiology. St. Louis, Mo: Elsevier Saunders. pp. 800–801.  
  18. ^ Kraegen EW, Chisholm DJ, Young JD, Lazarus L (March 1970). "The gastrointestinal stimulus to insulin release. II. A dual action of secretin". J. Clin. Invest. 49 (3): 524–529.  
  19. ^ Palmer KR, Penman ID (2010). "Alimentary track and pancreatic disease". In Colledge NR, Walker BR, Ralston SH. Davidson's Principles and Practice of Medicine (20th ed.). Edinburgh: Churchill Livingstone.  
  20. ^ Boron, Walter F. & Boulpaep, Emile L. (2012). "Acid secretion". Medical Physiology, 2e Updated Edition, 2nd Edition (2nd ed.). Philadelphia, PA: Saunders. p. 1352.  
  21. ^ "Human Secretin". Patient Information Sheets. United States Food and Drug Administration. 2004-07-13. Retrieved 2008-11-01. 
  22. ^ "Secretin stimulation test". MedlinePlus Medical Encyclopedia. United States National Library of Medicine. Retrieved 2008-11-01. 
  23. ^ "The Use of Secretin to Treat Autism". NIH News Alert. United States National Institutes of Health. 1998-10-16. Retrieved 2008-11-30. 
  24. ^ Sandler, A. D.; Sutton, K. A.; Deweese, J.; Girardi, M. A.; Sheppard, V.; Bodfish, J. W. (1999). "Lack of Benefit of a Single Dose of Synthetic Human Secretin in the Treatment of Autism and Pervasive Developmental Disorder". New England Journal of Medicine 341 (24): 1801–1806.  
  25. ^ Villanger O, Veel T, Raeder MG (March 1995). "Secretin causes H+/HCO3- secretion from pig pancreatic ductules by vacuolar-type H(+)-adenosine triphosphatase". Gastroenterology 108 (3): 850–859.  
  26. ^ Marinelli RA, Pham L, Agre P, LaRusso NF (May 1997). "Secretin promotes osmotic water transport in rat cholangiocytes by increasing aquaporin-1 water channels in plasma membrane. Evidence for a secretin-induced vesicular translocation of aquaporin-1" (PDF). J. Biol. Chem. 272 (20): 12984–12988.  
  27. ^ Chow BK, Cheung KH, Tsang EM, Leung MC, Lee SM, Wong PY (June 2004). "Secretin controls anion secretion in the rat epididymis in an autocrine/paracrine fashion". Biol. Reprod. 70 (6): 1594–1599.  
  28. ^ Cheng CY, Chu JY, Chow BK (September 2009). "Vasopressin-independent mechanisms in controlling water homeostasis". J. Mol. Endocrinol. 43 (3): 81–92.  
  29. ^ Lee VH, Lee LT, Chu JY, Lam IP, Siu FK, Vaudry H, Chow BK (December 2010). "An indispensable role of secretin in mediating the osmoregulatory functions of angiotensin II". FASEB J. 24 (12): 5024–32.  
  30. ^ Cheng CY, Chu JY, Chow BK (January 2011). "Central and peripheral administration of secretin inhibits food intake in mice through the activation of the melanocortin system". Neuropsychopharmacology 36 (2): 459–71.  

Further reading

  • Saus E, Brunet A, Armengol L, Alonso P, Crespo JM, Fernández-Aranda F, Guitart M, Martín-Santos R, Menchón JM, Navinés R, Soria V, Torrens M, Urretavizcaya M, Vallès V, Gratacòs M, Estivill X (October 2010). "Comprehensive copy number variant (CNV) analysis of neuronal pathways genes in psychiatric disorders identifies rare variants within patients". J Psychiatr Res 44 (14): 971–8.  
  • Bertenshaw GP, Turk BE, Hubbard SJ, Matters GL, Bylander JE, Crisman JM, Cantley LC, Bond JS (April 2001). "Marked differences between metalloproteases meprin A and B in substrate and peptide bond specificity". J. Biol. Chem. 276 (16): 13248–55.  
  • Lee LT, Lam IP, Chow BK (2008). "A functional variable number of tandem repeats is located at the 5' flanking region of the human secretin gene plays a downregulatory role in expression". J. Mol. Neurosci. 36 (1–3): 125–131.  
  • Nussdorfer GG, Bahçelioglu M, Neri G, Malendowicz LK (2000). "Secretin, glucagon, gastric inhibitory polypeptide, parathyroid hormone, and related peptides in the regulation of the hypothalamus- pituitary-adrenal axis". Peptides 21 (2): 309–324.  
  • Lossi L, Bottarelli L, Candusso ME, Leiter AB, Rindi G, Merighi A (December 2004). "Transient expression of secretin in serotoninergic neurons of mouse brain during development". Eur. J. Neurosci. 20 (12): 3259–69.  
  • Lee SM, Yung WH, Chen L, Chow BK (2005). "Expression and spatial distribution of secretin and secretin receptor in human cerebellum". NeuroReport 16 (3): 219–222.  
  • Lam IP, Lee LT, Choi HS, Alpini G, Chow BK (July 2009). "Bile acids inhibit duodenal secretin expression via orphan nuclear receptor small heterodimer partner (SHP)". Am. J. Physiol. Gastrointest. Liver Physiol. 297 (1): G90–7.  
  • Yamagata T, Aradhya S, Mori M, Inoue K, Momoi MY, Nelson DL (August 2002). "The human secretin gene: fine structure in 11p15.5 and sequence variation in patients with autism". Genomics 80 (2): 185–94.  
  • Lee LT, Tan-Un KC, Chow BK (2006). "Retinoic acid-induced human secretin gene expression in neuronal cells is mediated by cyclin-dependent kinase 1". Ann. N. Y. Acad. Sci. 1070 (1): 393–398.  
  • Onori P, Wise C, Gaudio E, Franchitto A, Francis H, Carpino G, Lee V, Lam I, Miller T, Dostal DE, Glaser SS (July 2010). "Secretin inhibits cholangiocarcinoma growth via dysregulation of the cAMP-dependent signaling mechanisms of secretin receptor". Int. J. Cancer 127 (1): 43–54.  
  • Lee LT, Tan-Un KC, Pang RT, Lam DT, Chow BK (July 2004). "Regulation of the human secretin gene is controlled by the combined effects of CpG methylation, Sp1/Sp3 ratio, and the E-box element". Mol. Endocrinol. 18 (7): 1740–55.  
  • Lu Y, Owyang C (2009). "Secretin-induced gastric relaxation is mediated by vasoactive intestinal polypeptide and prostaglandin pathways". Neurogastroenterol. Motil. 21 (7): 754–e47.  
  • Gandhi S, Rubinstein I, Tsueshita T, Onyuksel H (2002). "Secretin self-assembles and interacts spontaneously with phospholipids in vitro". Peptides 23 (1): 201–204.  
  • Love JW (2008). "Peptic ulceration may be a hormonal deficiency disease". Med. Hypotheses 70 (6): 1103–1107.  
  • Lam IP, Lee LT, Choi HS, Chow BK (2006). "Localization of small heterodimer partner (SHP) and secretin in mouse duodenal cells". Ann. N. Y. Acad. Sci. 1070 (1): 371–375.  
  • Luttrell LM (2008). "Reviews in molecular biology and biotechnology: transmembrane signaling by G protein-coupled receptors". Mol. Biotechnol. 39 (3): 239–264.  
  • Du K, Couvineau A, Rouyer-Fessard C, et al. (2002). "Human VPAC1 receptor selectivity filter. Identification of a critical domain for restricting secretin binding". J. Biol. Chem. 277 (40): 37016–37022.  
  • Portela-Gomes GM, Johansson H, Olding L, Grimelius L (1999). "Co-localization of neuroendocrine hormones in the human fetal pancreas". Eur. J. Endocrinol. 141 (5): 526–533.  
  • Mutoh H, Ratineau C, Ray S, Leiter AB (2000). "Review article: transcriptional events controlling the terminal differentiation of intestinal endocrine cells". Aliment. Pharmacol. Ther. 14 (Suppl 1): 170–5.  

External links

  • Overview at colostate.edu
  • Secretin at the US National Library of Medicine Medical Subject Headings (MeSH)
  • Physiology: 6/6ch2/s6ch2_17 - Essentials of Human Physiology
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.