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Physiological Control of Cholecystokinin Release And Gut 1996; 39: 661-667 661 Physiological control of cholecystokinin release and pancreatic enzyme secretion by intraduodenal Gut: first published as 10.1136/gut.39.5.661 on 1 November 1996. Downloaded from bile acids I Koop, M Schindler, A Bof3hammer, J Scheibner, E Stange, H Koop Abstract Keywords: bile acids, bile, pancreatic enzyme Background-The physiological rel- secretion, CCK-A receptor antagonist, evance of duodenal bile acids in the cholecystokinin, pancreatic polypeptide. control of cholecystokinin release and pancreatic enzyme secretion is still unknown. The control mechanisms ofthe intestinal phase Aim-To provide a near physiological of exocrine pancreatic secretion are complex. situation by perfusing a bile acid mixture Food components interact with digesting mimicking the individual endogenous bile factors, such as gastric acid, bile, and pancre- acid composition of the person under atic juice, and eventually come into contact investigation. For maximal reduction of with intestinal epithelial cells and probably endogenous bile output the CCK-A recep- sensory nerve endings causing release of tor antagonist loxiglumide was infused hormones and activation of neurones, intravenously. which in turn regulate exocrine pancreatic Subjects and Methods-Seven healthy secretion. volunteers were studied on four different In humans, one of the most potent local days by a duodenal marker perfusion luminal regulators of exocrine pancreatic se- technique. The individual bile acid com- cretion was found to be bile. However, results position in duodenal juice and test meal differ with respect to the effect of bile and bile stimulated bile acid output was assessed acids on basal stimulated exocrine pancreatic on day 1. Bile acids were perfused at an secretion. Basal secretion was reported to be of or determined on enhanced whereas stimulated amount 30 100% as by bilel` pancre- http://gut.bmj.com/ day 1 in combination with the test meal in atic secretion was either unaltered4 or inhib- the presence or absence of loxiglumide. ited.5 6 The most important hormone involved Pancreatic enzymes, bilirubin, and bile in the regulation of exocrine pancreatic se- acid output were determined in duodenal cretion is cholecystokinin (CCK), which juice. Plasma cholecystokinin (CCK) and accounts for about 50% of postprandially plasma pancreatic polypeptide (PP) were released pancreatic enzymes.7 8 In addition, measured radioimmunologically. CCK is the predominant mediator of gall on October 2, 2021 by guest. Protected copyright. Department of Results-Bile acid perfusion did not signi- bladder contraction. Postprandial duodenal bile Internal Medicine, ficantly alter stimulated pancreatic en- content is reduced to about 5% of infusion of University Hospital, Marburg, Germany zyme, bilirubin or bile acid output or the highly specific CCK-A receptor antagonist M Schindler plasma CCK. Loxiglumide did not alter loxiglumide.7 8 Bile acids in turn have been A Bol3hammer basal CCK release but increased test meal found to inhibit stimulated CCK release.4 9 stimulated CCK output fourfold (p<0.05). One crucial point about all the studies Department of Internal Medicine, The addition of bile acids to the test meal investigating the effect of bile acids on either Klinikum Buch, at a dose resembling 30% of bile acid exocrine pancreatic secretion or plasma CCK Berlin, Germany output as determined on day 1 prevented release is the use of supraphysiological concen- H Koop this increase. Plasma PP concentration trations and amounts of bile acids. Further- Department of remained unchanged by bile acids and more, in most studies sodium taurocholate and Internal Medicine, were mostly undetectable during loxi- chenodeoxycholic acid were used as single bile University Hospital, Lubeck, Germany glumide infusion. acids each accounting for only 150/6-30% of all J Scheibner Conclusion-The CCK producing cell is bile acids secreted.'2 13 Thus, the physiological S Stange under constant suppression by intraduo- relevance of luminal bile acids in the regulation Department of denal bile acids which cannot be further of exocrine pancreatic secretion and CCK Internal Medicine, enhanced by a physiological bile acid release is still largely unknown. University Hospital mixture. However, removal of duodenal The purpose of our study was to provide a Charite, Berlin, Germany bile acids by inhibition of gall bladder near physiological situation by duodenal per- I Koop contraction unmasks this suppression fusion of a bile acid mixture mimicking the Correspondence to: leading to a dramatic increase in plasma individual endogenous bile acid composition Dr I Koop, CCK levels. As little as one third of post- and concentration of the person under investi- IV. Medical Department, Division of Gastroenterology, prandially released bile acids completely gation. Endogenous bile acid output was University Hospital Charite, reverse this effect. Bile acids are the most reduced by inhibiting gall bladder contraction Humboldt-University, Berlin, Germany. important luminal regulator of CCK by infusion of the highly specific CCK-A Accepted for publication release in humans. receptor antagonist loxiglumide.14 15 We were 11 June 1996 (Gut 1996; 39: 661-667) thereby able to show that duodenal bile acids 662 Koop, Schindler, BoJ3hammer, Scheibner, Stange, Koop are of minor importance in the regulation of stimulation period was used to calculate bile postprandial pancreatic enzyme secretion but acid perfusates on the following days. are a key regulator of stimulated CCK release. Bile acids appear to exert a constant inhibitory tone on the intestinal CCK producing cell. Day 2 Gut: first published as 10.1136/gut.39.5.661 on 1 November 1996. Downloaded from During the first hour of the stimulation period the liquid test meal was mixed with 30% ofbile Methods acid output as determined on day 1. The bile acid mixture comprised all the bile acids SUBJECTS identified in the duodenal function from day 1 Seven healthy male volunteers aged 22-27 had mixed according to their individual pro- given informed written consent to participate portions. During the second hour of the stimu- in this study. The protocol had been approved lation period the test meal was perfused by the local ethical committee of the Medical without bile acids. Via an indwelling venous Faculty of the Philipps-University of Marburg. catheter in the forearm, a continuous in- fusion of saline was given over the whole study time. Experimental protocol On the morning after an overnight fast a triple- lumen tube was positioned with its tip in the Day 3 distal part ofthe duodenum under fluoroscopic During the first hour of the stimulation period guidance. The most proximal lumen ended in the liquid test meal was mixed with 100% of the gastric antrum and was used for continuous the bile acid output determined on day 1. The aspiration of gastric acid. The second lumen bile acid mixture comprised all the bile acids terminated in the middle part ofthe duodenum identified in the duodenal fraction from day 1 close to the Papilla of Vateri and served as mixed according to their individual pro- perfusion site for the recovery marker poly- portions. Over the second hour of the stimu- ethylene glycol (PEG 4000, dissolved in 0.9% lation period the test meal was perfused with- saline) and for the liquid test meal plus PEG out bile acids. Saline was infused intravenously with or without bile acids. The perfusion rate over the whole experimental period. was 2 ml/min. Duodenal contents were con- tinuously collected via the third lumen, which was located 10 cm distally to the perfusion site. Day 4 Samples were obtained at 15 minute intervals, Duodenal perfusion during the basal and stored on ice, and immediately processed for stimulation period was performed according to determination of pancreatic enzymes. Aliquots the conditions on day 2. Instead of saline, of duodenal juice were stored at -30°C for however, the CCK-A receptor antagonist loxi- http://gut.bmj.com/ future measurements of bilirubin and bile acid glumide was infused intravenously at a rate concentration. Via an indwelling venous of 10 mg/h per kg body weight. Infusion of catheter in the forearm, blood was drawn into loxiglumide was started at the beginning EDTA-containing tubes at 15 minute intervals of the basal period. According to previous and stored on ice. Immediately after the end of measurements maximum steady state plasma the experiment the blood was centrifuged and concentrations of loxiglumide are achieved the plasma stored at -30°C until hormone after 45-60 minutes of intravenous in- on October 2, 2021 by guest. Protected copyright. determination. fusion.7 During the whole experiment the volunteers Days 2 and 4 were performed in random lay in a recumbent position. Perfusion of PEG order. was started as soon as the tube was positioned. Equilibration lasted between 60 and 90 min- utes until the duodenal juice was clear, enzyme BILE ACID COMPOSITION output had declined, and stable conditions had The individual bile acid compositions were been achieved. determined in duodenal aspirates using high The duodenal stimulation period lasted for pressure liquid chromatography.'6 In three 120 minutes and perfusion of stimuli was per- volunteers, the day to day variation in bile acid formed according to the protocol outlined composition was investigated. Over two weeks below. Each volunteer was studied on three no significant variation in bile acid composition different ways. Four of them participated in a was observed. Furthermore, it has been shown fourth study. by others that day to day variation in bile acid composition is negligible.'3 Day 1 Aliquots of the first two fractions of unstimu- ENZYME, BIIE ACID, BILIRUBIN, AND PEG lated duodenal juice were processed for deter- MEASUREMENTS mination of individual bile acid composition. The volume of gastric and duodenal samples Stimulation was performed by infusion of a was determined to the closest millilitre and liquid test meal (18 g soybean oil, 15 g protein, corrected for loss by reference to PEG recovery 40 g glucose, 300 ml water) over 120 minutes (see under Calculations and statistics below).
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