What we gastroenterologists must (should) know about pancreatic physiology

1. What we gastroenterologists must (should) know aboutpancreatic physiology Joachim Mössner University of Leipzig Prague, April 16, 2010

2. Physiology of Pancreatic Enzyme Secretion • Pancreas synthesizes and secretes digestive enzymes and secretes HCO3 • Both are necessary for normal digestion • Pancreas stimulated acutely by feeding: • Neuronal Mechanisms: Vagus mediates small cephalic phase • Importance of vagal afferents • Vagal-vagal reflexes • Acinar cells have M1 and M3 receptors • Some direct innervation of pancreas from gut JM 2010

3. The pancreas is made up of three functional components: • Endocrine – Islets 2% • Exocrine – Acinar 80% Digestive Enzyme • Exocrine - Ducts 8% Bicarbonate Rich Fluid • Innervation • Vagal: Acetylcholine main transmitter • Acini • Ducts • Islets • Sympathetic: Norepinephrine main transmitter • Islets • Blood Vessels JM 2010

4. Pancreas JM 2010

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8. Paracrine stimulation within the mucosa Endocrine stimulation JM 2010

9. Cholecystokinin, CCK • CCK or CCK-PZ; Greek chole, "bile"; cysto, "sac"; kinin, "move"; move the gallbladdder • Peptide hormone of the gastrointestinal system & brain • Stimulation of digestion of fat & proteins • CCK, previously called pancreozymin, synthesized by I-cells in the mucosa of small intestine • Secreted from the first segment of the small intestine • Role in inducing drug tolerance to opioids? JM 2010

10. Cholecystokinin, CCK • Stimulation of release from I-cells by oligopeptides, certain amino acids (phenylalanine), fatty acids • Stimulation of release by releasing peptides present in pancreatic secretions and duodenal mucosa (monitor peptide, …)? • Negative feedback inhibition: • Destruction of CCK releasing peptides by trypsin JM 2010

11. Cholecystokinin, CCK • Inhibition of gastric emptying & gastric acid secretion • Stimulation of pancreatic acinar cells to secrete pancreatic digestive enzymes, hence the old name pancreozymin • Stimulation of human acinar cells directly via CCK-A receptors? • Stimulation indirectly via CCK-B receptors of nerves: release of acetylcholine JM 2010

12. Cholecystokinin, CCK • Enzymes catalyze digestion of fat, protein, & carbohydrates • As levels of substances that stimulate release of CCK drop, concentration of the hormone drops as well • Release of CCK inhibited by somatostatin, PYY, … • CCK causes increased production of hepatic bile • CCK stimulates contraction of gall bladder & relaxation of the sphincter of Oddi • Bile salts form amphipathic micells that emulsify fats • Triglyceride digestion needs lipase, bile salts, colipase: 2 fatty acids, 1 monoglyceride JM 2010

13. Endocrine Mechanisms • CCK: • Paracrine stimulation of vagal afferents • Endocrine effect through blood • Whether human acinar cells have CCK receptors is controversial JM 2010

14. Secretin • Major stimulant of HCO3 secretion • Insulin • Released from islets. Acts on exocrine cells by portal blood system • Nutrients • Supply energy, building blocks and amino acids • Act as a anabolic signal • What ends Secretion? • Exit of food from upper small intestine • Feedback inhibition by surplus trypsin in intestinal lumen • Ileal brake JM 2010

15. REGULATION OF PANCREATIC SECRETION JM 2010

16. Stimulus-secretion Coupling ofPancreatic Enzyme Secretion JM 2010

17. INTRACELLULAR TRANSPORT OF PANCREATIC SECRETORY PROTEINS JM 2010

18. Secretin • First hormone identified by William Bayliss & Ernest Starling in 1902 • Produced in S cells of the duodenum in the crypts of Lieberkühn • Secretin encoded by the SCT gene • Protein with 27 amino acids • Release by gastric acid entering the duodenum JM 2010

19. Secretin • Stimulation of watery bicarbonate secretion from, Brunner glands of the duodenum, pancreatic duct cells & acinar cells (?) • Inhibition of gastric acid secretion by inhibition of gastrin release • Stimulation of adenylate cyclase activity:cAMP second messenger • Control of water homeostasis throughout the body • Regulation of pH of duodenal contents via control of gastric acid secretion & buffering with bicarbonate • Role in osmoregulation in the hypothalamus, pituitary, & kidneys JM 2010

20. Mechanism of Pancreatic Bicarbonate Secretion JM 2010

21. Regulation of Protein Synthesis in the Pancreas ACh receptor PI3-K Insulin receptor CCK receptor Phosphatase Akt/PKB eEF2 eEF2 (Active) (Inactive) Amino acids eEF2K (off) mTOR Complex 1 Kinase p70 s6k eIF4E eIF4E 4E-BP1 4E-BP1 S6 Ribosomal protein 40 S eIF4A Stop AAAAA mRNA AUG m7GTP eIF4G 60 S 80 S initiation complex

22. Concentration of Ions in Pancreatic Juiceas a Function of Flow JM 2010

23. CFTR Trypsin(ogen) Trypsininhibitor Duct Cell Acinar Cell Function of the Exocrine Pancreas JM 2010

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25. Trypsin Trypsin Inhibitor JM 2010

26. N- Ala-Pro-Phe-Asp-Asp-Asp-Asp-Lys- A16V D19A D22G K23R Trypsinogen Activation Peptide N29I R122H N- -C * * * * * * * * * * * * * * * * * * TAP JM 2010

27. Activation of Pancreatic Proenzymes in the Intestine involves Enterokinase and activated Trypsin JM 2010

28. Pancreatic Bicarbonate output increases in responseto low Duodenal pH JM 2010

29. CCK Amino Acids MAPKs Ca2+ mTOR calcineurin eIF4E 4E-BP1 mRNA ? S6K1 eIF4E NFATs NFATs Transcriptional Control of Gene Expression Translational Control of Protein Synthesis Pancreatic Growth (Mitogenesis & Hypertrophy) Regulation of Growth of the Pancreas JM 2010

30. Long term effects of hormones and nutrients • Adaptive Growth as in pregnancy, lactation and high protein diet • Regeneration • Limited after partial resection or fibrosis • Nearly complete after mild acute pancreatitis • Newer Material • Role of Vagal afferents in responding to nutrients and CCK • Feedback inhibition on CCK release and pancreatic secretion by active trypsin in lumen • Mechanism of high HCO3 secretion • Importance of nutrients particularly amino acids for the pancreas • Question of enteral vs parenteral feeding JM 2010

31. Somatostatin • Somatostatin (growth hormone-inhibiting hormone, GHIH, somatotropin release-inhibiting factor, SRIF) • Peptide hormone • Regulation of the endocrine system • Affects on neurotransmisson & cell proliferation • Interaction with G-protein-coupled somatostatin receptors • Two active forms produced by alternative cleavage of a single preproprotein: one of 14 amino acids, the other of 28 amino acids JM 2010

32. Somatostatin: Stomach JM 2010

33. Somatostatin • Inhibition of release of numerous secondary hormones • gastrin, CCK, secretin, motilin, VIP, GIP, enteroglucagon • Lowers rate of gastric emptying • Reduces smooth muscle contractions & blood flow within the intestine • Suppresses release of pancreatic hormones • Inhibits insulin release when somatostatin is released from granules in alpha-1 cells of pancreatic islets of Langerhans • Inhibits release of glucagon • Suppresses exocrine pancreatic secretion JM 2010

34. Pancreatic Polypeptide • Secreted by PP cells predominantly in the head of the pancreas • 36 amino acids • Function: selfregulation of pancreas secretion activities (endocrine and exocrine) • Effects on hepatic glycogen levels & gastrointestinal secretions • Secretion in humans increased after a protein meal, fasting, exercise & acute hypoglycemia, decreased by somatostatin & intravenous glucose JM 2010

35. Peptide Tyrosin Tyrosin, PYY • Released by the ileum • Inhibition of pancreatic enzyme secretion JM 2010

36. 100 l l 75 l l l l 50 l l Fecal fat, % l l 25 l l l Upper limit of normal l l l l l l l l l l l l l l l l 0 0 25 50 75 100 125 Lipase output, % normal Duodenal Lipase and SteatorrheaDiMagno et al: N Engl J Med 1973;288:813 JM 2010

37. Negative Feedback Inhibition ofPancreatic Enzyme Secretion Proteases destroy CCK releasing peptides Plasma CCK Enzyme secretion Pancreatic duct pressure Pain JM 2010

38. Palliation of Pain in Chronic Pancreatitis:Use of Enzymes • Metaanalysis • 6 randomized, double blind, placebo controlled studies • Statistical analysis demonstrates no benefit for pancreatic enzymes Mossner: Surg Clin North Am 1999; 79: 861-72 JM 2010

39. Genes and Pancreatitis • Hereditary chronic pancreatitis • Mutations: cationic trypsinogen • Cystic fibrosis • CFTR-mutations • Idiopathic chronic pancreatitis • Mutations of CFTR: special form of cystic fibrosis • Mutations or trypsin inhibitor SPINK • Chymotrypsin C mutations • Tropical pancreatitis • SPINK-mutations, CTRC-mutations • Alcohol induced chronic pancreatitis • Polygenetic disease? • Role of protective mutations? JM 2010

40. Risk Factor: Chymotrypsin C • p.R254W & p.K247_R254del overrepresented in pancreatitis • 30 / 901 3.3% with idiopathic or hereditary pancreatitis vs • 21 / 2,804 0.7% controls • Replication study in alcohol-related diseases: • 10 / 348 2.9% in chronic pancreatitis vs • 3 / 432 0.7% in liver disease • Indian subjects with tropical chronic pancreatitis: • 10 / 71 14.1% vs • 1 / 84 1.2% control • OR = 13.6; CI = 1.7-109.2; P = 0.0028 • Rosendahl, Witt, …. Mössner, Teich, Sahin-Toth: Nature Genetics 2008; 40: 78-82 JM 2010

41. Risk Factor: Chymotrypsin C JM 2010

42. Summary & Conclusion • CCK: Stimulator of digestive enzyme secretion • Directly via CCK-A receptors on acinar cells (?) • Indirectly via CCK-B receptors: acetylcholine release • CCK: Stimulator of gallbladder contraction • Secretin: Stimulator of bicarbonate secretion • Activation of trypsinogen by enterokinase • Activation of proenzymes by trypsin • Termination of enzyme secretion: • Negative feedback (destruction of CCK releasing peptides by trypsin ?) • Ileal brake (PYY, somatostatin) JM 2010

43. I would like to thank my former mentor John A. Williams, MD, PhD Professor of Medicine and Physiology Ann Arbor, Michigan for providing me several of the slides and teaching me in pancreatic physiology during my stay in San Francisco 1983 - 1985 JM 2010

44. 600 Years University of Leipzig dies academicus, December 2, 2009 Pancreas Group Leipzig Hans Bödeker Sebastian Gaiser Albrecht Hoffmeister Volker Keim Jonas Rosendahl Lena Selig Niels Teich JM 2010