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PDF Hosted at the Radboud Repository of the Radboud University Nijmegen PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/24784 Please be advised that this information was generated on 2021-09-26 and may be subject to change. Regulation of gastric and pancreatic lipase secretion by CCK and cholinergic mechanisms in humans JAN BOROVICKA, WERNER SCHWIZER, CHRISTINE METTRAUX, CHRISTIANNA KREISS, BRIGITTE REMY, KHALED ASAL, JAN B. M. J. JANSEN, ISABELLE DOUCHET, ROBERT VERGER, AND MICHAEL FRIED Gastroenterology Department, Policlinique Médicale Universitaire, Lausanne; Gastroenterology Department, University Hospital, Zurich, Switzerland; Gastroenterology Department, University Hospital, Nijmegen, The Netherlands; and Laboratoire de Lipolyse Enzymatique du Centre National de la Recherche Scientifique, Marseille, France Borovicka, Jan, Werner Schwizer, Christine Met- these studies showed an inhibitory action of endog­ traux, Christianna Kreiss, Brigitte Remy, Khaled Asal, enous CCK on gastric acid secretion in contrast to the Jan B. M. J. Jansen, Isabelle Douchet, Robert Verger, known stimulatory effect of CCK on pancreatic enzyme and Michael Fried. Regulation of gastric and pancreatic secretion in humans (2, 17). Although postprandial lipase secretion by CCK and cholinergic mechanisms in CCK-dependent regulatory mechanisms have been stud­ humans. Am. J. Physiol. 273 (Gastrointest. Liver Physiol. 36): ied extensively for the pancreas, no data are available G374-G380,1997.—Gastric lipase (HGL) contributes signifi­ cantly to fat digestion. However, little is known about its for gastric enzyme secretions in humans. neurohormonal regulation in humans. We studied the role of In this study we therefore applied the cholinergic CCK and cholinergic mechanisms in the postprandial regula­ antagonist atropine and the highly specific CCK-A tion of HGL and pancreatic lipase (HPL) secretion in six receptor antagonist loxiglumide (36), which has been healthy subjects. Gastric emptying of a mixed meal and shown to inhibit markedly pancreatic enzyme secretion outputs of HGL, pepsin, acid, and HPL were determined with and gallbladder contraction in humans (2). Our aim a double-indicator technique. Three experiments were per­ was to define the physiological role of CCK and cholin­ formed in random order: intravenous infusion of 1 ) placebo, ergic mechanisms in the regulation of postprandial 2) low-dose atropine (5 /£g-kg~-h-1), and 3) the CCK-A gastric enzyme secretions in comparison to pancreatic receptor antagonist loxiglumide (22 /zmol • kg- •h-1). Atropine enzyme secretions and to study the relationship be­ decreased postprandial outputs of HGL, pepsin, gastric acid, tween the secretion of HGL and pancreatic lipase and HPL (P < 0.03) while slowing gastric emptying (P < (HPL) after a physiological meal in humans. 0.05). Loxiglumide markedly increased the secretion of HGL, pepsin, and acid while distinctly reducing HPL outputs and MATERIALS AND METHODS accelerating gastric emptying (P < 0.03). Plasma CCK and gastrin levels increased during loxiglumide infusion (P < Subjects 0.03). Atropine enhanced gastrin but not CCK release. Post­ prandial HGL, pepsin, and acid secretion are under positive Studies were performed in six healthy subjects (5 men, 1 cholinergic but negative CCK control, whereas HPL is stimu­ woman) between 23 and 30 yr of age and 76 kg mean body lated by cholinergic and CCK mechanisms. We conclude that weight (range 60-83 kg). All subjects were within 10% of CCK and cholinergic mechanisms have an important role in their ideal body weight. No subject was taking any medica­ the coordination of HGL and HPL secretion to optimize tion, nor did any subject have a history of gastrointestinal digestion of dietary lipids in humans. symptoms or prior surgery. The studies were approved by the local ethical committee of the University Hospital of Lau­ loxiglumide; atropine; pepsin; acid secretion; gastric empty­ sanne, and all subjects gave written informed consent. ing Experimental Procedure Double-indicator technique. All studies were performed THE EXISTENCE OF gastric lipolysis has been known after an overnight fast. The subjects were intubated with a triple-lumen tube (5 mm OD), with the aspiration site (tip) at since the beginning of this century (41). Recently, the the ligament of Treitz. A marker perfusion site was located 20 cellular origin of human gastric lipase (HGL) has been cm proximal to the tip, and the third canal of the tube ended localized in the chief cells of fundic mucosa (28). HGL in the antral portion of the stomach. A separate single-lumen has been shown to be responsible for 25% of acyl chain nasogastric tube (3 mm OD) was placed in the most depen­ hydrolysis during meal digestion (8). The colocation of dent part of the stomach. The final position of the tubes was HGL and pepsin and their correlated secretory re­ verified by fluoroscopy. With the subjects comfortably seated, sponse to pentagastrin stimulation suggested common an infusion of polyethylene glycol (PEG) 4000 (1.5 g PEG/100 regulatory mechanisms of these two gastric enzymes ml, 0.154 mol/1 saline) was begun through the proximal port (28, 39). Distinct receptors of the two important regula­ of the duodenal tube at a rate of 1.5 ml/min. Duodenal tory hormones, cholecystokinin (CCK) and gastrin, contents were aspirated continuously during the experiments by means of a suction pump, which provided intermittent were previously identified in chief cells in the guinea negative pressure. After an equilibration period, two premeal pig stomach (10). Recently, different study groups re­ samples were collected from the duodenal tube in 15-min ported data on the regulation of gastric acid secretion periods. Before meal administration the stomach was com­ by CCK in dogs and humans (22, 35). By use of specific pletely emptied by manual aspiration with a 50-ml syringe CCK-A receptor antagonists (loxiglumide, MK-329), through the nasogastric and the proximal channel of the G374 0193-1857/97 $5.00 Copyright © 1997 the American Physiological Society POSTPRANDIAL REGULATION OF GASTRIC AND PANCREATIC LIPASE G375 triple-lumen tube. A 500-ml mixed liquid test meal (Ensure, The specific activities of HGL and HPL measured at Abott, Chicago, IL; diluted with 100 ml of distilled water) different pH values are shown in Pig. 1, demonstrating an containing 16.8 g of protein, 13.4 g of fat, 53.4 g of carbohy- assay optimum for HPL at pH 8.0 and for HGL at pH 5.6. The drate, and a total caloric value of 400 kcal (254 mosmol/1, pH activity of HPL was measured at pH 8.0 (specific activity = 7.0) was labeled with 99mTc-diethylenetriaminepentaacetic 1,785 U/mg purified HPL) using 1.5 ml of an emulsion acid and infused intragastrically through the nasogastric containing 1.5 ml of triolein (Fluka, Buchs, Switzerland) in 35 tube over a standardized 7-min period. ml of buffer with 1 mM taurochenodeoxycholate, 9 mM Sample collection. Gastric samples (10 ml) were collected taurocholate, 0.1 mM cholesterol, 1 mM phosphatidylcholine, at the end of each 15-min period via the nasogastric tube by 15 mg of bovine serum albumin per milliliter (free fatty acid means of a 20-ml syringe. Duodenal samples were continu- free), 2 mM tris(hydroxymethyl)aminomethane, 100 mM ously siphoned on ice during 15-min periods after meal NaCl, and 0.2 mM CaCl2 (18). The interassay variation (n = administration. Separate aliquots of gastric and duodenal 18) for HPL measurements was 6.4%, and the intra-assay juices were treated as follows. Native gastric and duodenal variation (n ~ 5) was 1.1%. samples were used for analysis of pH, acid content, PEG, and In duodenal samples, HGL and HPL activity could be 99mTc. For optimal storage conditions the pH of gastric and accurately discriminated. By lowering the pH of duodenal duodenal samples was adjusted to 4-5 for analysis of HGL. To samples to 2 at 1 h before the HGL assay, HGL activity was prevent proteolytic inactivation, turkey egg white inhibitor slightly increased [104 ± 1% (SE), n = 8], whereas HPL was (10 mg/ml) was added to gastric and duodenal samples (23) completely inactivated and not measurable under standard immediately after collection. Glycerol (50% vol/vol) was added assay conditions (Fig. 2). Furthermore, HGL activity was to gastric samples for later pepsin measurements and to shown not to be influenced by the proteolytic action of pepsin duodenal samples for HPL analysis. All duodenal samples when pure pepsin was added to gastric juice during a 1-h were assayed within 1 mo for HGL and HPL activity. HGL incubation period at pH 2, confirming previous observations showed no loss in activity after 1 and 2 mo when stored under (29). The HPL determination was highly specific, inasmuch the above conditions. Blood was sampled through a separate as HGL and carboxyl ester lipase are not active under HPL indwelling venous catheter at -30, -20, and -10 min and at standard assay conditions using the long-chain triacylglyc- 10, 20, 30, 45, 60, 90, 120, 150, and 180 min after meal erol triolein as substrate (17). Furthermore, HPL was mea- administration. Blood samples were collected in 10-ml tubes sured at its pH optimum of 8.0, whereas HGL was determined containing 16 mg of EDTA and 8,000 U of aprotinin and were at its optimal pH of 5.6. immediately centrifuged (4°C, 3,000 rpm, 15 min). Immedi- HGL and HPL activities are expressed in international ately after these different procedures, all samples were frozen units per milliliter (1 U = 1 ^mol of fatty acids released per on dry ice and stored at -20°C until they were assayed. minute). Furthermore, concentrations of the two lipases are also expressed in milligrams of protein of the respective Experimental Protocol lipase.
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