Pancreatic Polypeptide and Intestinal Migrating Motor Complex in Humans

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1 GASTROENTEROLOGY 1983 ;84:10-7 Pancreatic Polypeptide and Intestinal Migrating Motor Complex in Humans Effect of Pancreaticobiliary Secretion CHUNG owyang, SAMI R. ACHEM-KARAM, and AARON 1. VINIK Department of Internal Medicine, Division of Gastroenterology and Division of Endo crin ology and Metabolism, and the Department of Surgery, The University of Michigan, Ann Arbor, Michigan There is a good correlation between pancreatic pol y peptide release and pancreatic exocrine secretion in response to hormone and nutrient stimulation. During interdigestive periods, cyclic fluctuations of pancreatic and biliary secretions are associated with maximal activity (phase 3) of the intestinal migrating motor complex. In this study we determined whether the changes in fasting plasma pancreatic polypeptide levels are associated with secretory and motor events in the duodenum and the role of pancreatico-biliary secretion in pancreatic pol ypeptide release. Gastroduodenal motor activity, pancreatic enzyme and bile acid output, and plasma pancreatic polypeptide were studied in 10 fasting healthy subjects using the gastroduodenal intubation and perfusion method with strain-gauge pressure transducers positioned in the antrum, midduodenum, and jejunum. Four phases of duodenal interdigestive motor activity were identified. During phase 1 outputs of trypsin (5 ± 1 k Ulh) and bile acid (72 ± 14 IJ-mollh) were minimal. Durin g late phase 2, maximal output of trypsin (36 ± 4 kulh) and bile acid (948 ± 268 IJ-mollh) occurred and continued into phase 3, followed by a rapid decline of trypsin (8 ± 2 kulh) and bile acid (50 ± 12 IJ-mollh) secretion during phase 4. There were wide intra- and interindividual variations in fasting plasma pancreatic polypeptide concentrations. However these fluctua- Received March 22, Accept ed August 4, Address requests for reprints to: Chung Owyang, M.D., Gastroenterology Research Unit, University of Michig an Medical Cent er, Ann Arbor, Michigan This investigation was supported by U.S. Pub lic Health Service grants AM-00B88 from the National Inst itute of Arthritis, Metabolism, and Digestive Diseas es, Michi gan Diabetes Research and Training Center Grant 5P60-AM-20572, and grant 5MOI-RR from the General Clinical Research Program by the American Gastroenterological Association /83/ $03.00 tions appeared to be associated with cyclic changes of pancreatic and biliary secretions. Low plasma pancreatic pol ypeptide levels (26 ± 4 pg/ml) were present during phase 1, and levels started to increase during phase 2 (108 ± 10 pg/ml), reaching a peak in early phase 3 (143 ± 16 pg/ml). A rapid decline to low values (38 ± 6 pg/ml) occurred during phase 4. In a separate set of experiments in six healthy subjects, intraduodenal perfusion of pancreatico-biliary juice at 10 mllmin for 5 min, 30 min after a previous period of phase 3 motor activity, stimulated the release of pancreatic pol ypeptide (mean peak increase = 166 ± 22 pg/ml) into th e circulation. This was accompanied by an increased pancreatic trypsin and bile acid output similar to that observed during phase 3 activity. Neither the ph, osmolarity, nor protein content of the juice accounted for the response. We conclude that there are cyclic fluctuations offasting plasma pancreatic polypeptide levels in humans that are associated with bursts of pancreatic and biliary secretion into the duodenum and maximal activity of the migrating motor complex in the proximal gut. There is an undefined factor(s) in the pancreatico-biliary juice that stimulates plasma pancreatic polypeptide release. These observations support the possibility that pancreatico-biliary secretion, pancreatic polypeptide release, and motor activity during the interdigestive period are causally related. Under basal conditions, rates of pancreatic exocrine secretion are low. In 1911, Boldyreff (1) reported that in fasting dogs, cyclic secretion of pancreatic juke corresponds to the period of maximal intestinal contraction. Recently this phenomenon has been rediscovered (2,3) and demonstrated to occur also in humans (4). Bursts of pancreatic and biliary flow

2 January 1983 THE PANCREAS AND DUODENAL MOTILITY 11 into the duodenum take place just before the sweeping actions of the gastroduodenal migrating motor complex (MMC), which occur every min during the interdigestive periods. Human pancreatic pol ypeptide (PP) is found in both the exocrine and endocrine pancreas (5). Its release closely parallels pancreatic exocrine secretion (6). In this study, we determined whether the increase in fasting PP levels is associated with an increase in pancreatic and biliary secretion and the periodicity of the MMe, and investigated the role of pancreatico-biliary secretion in PP release during the interdigestive state. MElHOO Methods and Materials Ten healthy male volunteers, yr old, participated in the studies. All subje cts were within 10% of their ideal body weight; none were taking any medication, or had a history of gastrointestinal symptoms and surger y. The studies were approved by the University of Michigan Human Use Committee on February 12,1981, and written informed consent was obtained in each case. Perfusion Transducers In all experiments, gastrointestinal motor activity was measured by a highly sensitive transducer assembl y previously described (7). It consisted of three miniature strain-gauge pressure transducers (Millar Instruments, Houston, Tex., Model PC 3S0) attached in a series to a double-lumen polyvinyl intestinal tube that facilitated positioning of the pressure sensors in the antrum and proximal bowel and allowed simultaneous perfusion and aspiration of the duodenum. The sensor tips were attached I, 10, and 38 ern from the tip of the tube. Before each study, the transducers were connected to a Gould pen recorder (Gould Inc., Instruments Div., Cleveland, Ohio, Model 2400) and calibrated using the transducer control unit (Millar Instruments, Model TC 100). Procedure The study was comprised of two parts : In part I, gastroduodenal motor activity, pancreatic and biliary secretion, and plasma PP were studied in 10 fasting healthy subjects using the gastrointestinal intubation and perfusion method with strain-gauge pressure transducers located in the antrum, midduodenum, and proximal jejunum. In part 2, the plasma PP response to intraduodenal perfusion of human pancreatico-biliary juice was investigated in six healthy subjects. Part 1. Ten healthy subjects participated in this group of studies. They were admitted to the University of Michigan Clinical Research Center, and all studies were performed after an overnight fast. Gastrointestinal intubation was performed under fluoroscopic control. The distal transducer was placed in the proximal jejunum just distal to the ligament of Treitz, and the middle and proximal Figure 1. Peroral gastric and intestinal tube assemblies used in this study. Duodenal perfusion and aspiration sites and position of pressure transdu cers are indicated. transducers were positioned in th e midduodenum and antrum, respectively (Figure 1). The same double-lumen intestinal tube to which the transducers were attached was also used for simultaneous perfusion and aspiration of the duodenum for quantification of pancreatic and biliary secretion. The duodenal perfusion site was located at the midduodenum, 2 em proximal to the duodenal transducer, and the aspiration site was placed 10 em distally at the ligament of Treitz (Figure 1). A gastric sump tube was also introduced with its orifice situated at the gastric antru m for continuous gastric aspiration. The average rad iation exposure to the abdomen during fluoroscopy was 0.6 rad per study. After intubation, all studies were started between 8:30 and 9:30 AM, and sub jects were studied in a semireclining posture (45 to the hor izontal). A 19-9auge intracath needle was inserted into an ante cubital vein for blood sampling. This was kept patent by a fluid lock containing a dilute solution of heparinized saline (100 U/ml). The motor activity of the antrum and proximal small bowel was recorded continuously for at least 6 h. The duodenal perfusion solution was normal saline containing a nonabsorbable marker, polyethylene glycol (PEG 4000) (S gil), warmed to 37 C and adjusted to ph 7.0. The duodenum was perfused at 10 nil/min, and duodenal juice was collected at the level of the ligament of Treitz by constant suction (-20 mmhg). The samples of juice were collected for IS-min periods and kept on ice during phase 1 and 2 activity. Phase 3 activity was used as the reference point.

3 12 OWYANG ET AL. GASTROENTEROLOGY Vol. 84, No.1 Because the duration was 4 ± 1.5 min, duodenal samples were pooled during each phase 3 period. In the period immediately after phase 3, phase 4 activity was short (2 ± 0.6 min), and duodenal juice was also pooled. A 5-10-ml aliquot of the juice was retained for analysis, and the remainder was returned to the jejunum. Blood sampling was performed at 15-min intervals and at the beginning and end of each phase 3 period and once with the succeeding phase 4 period during the entire study. Each study was begun after the duodenum had been perfused for at least 1 h to establish an equilibrium state, com menced at the beginning of phase 1 duodenal motor activity, and lasted for at least three interdigestive cycles. The mean duration of a complete cycle (between two episodes of phase 3 activity) was computed based on three interdigestive cycles per subject, and periodicity was measured after the appearance of the first phase 3 activity in the duodenum following intubation. Part 2. Six of the ten subjects studied in part 1 participated in the second group of studies. Subjects were admitted to the Clinical Research Center for a 2-day study. The first day was used to collect pancreatico-biliary juice from the duodenum after stimulation by octapeptide of cholecystokinin (CCK-B) (Sincalide; E.R. Squibb and Sons, Inc., Princeton, N.].). After intubation with a single-lumen duodenal tube and a gastric sump tube, each subject received an intravenous infusion of CCK-B at a dose of 40 ng/kg-h, Pancreatico-biliary secretion was aspirated from the duodenum at the ligament of Treitz. Gastric secretion was continuously aspirated by a gastric sump tube. The aspirated duodenal juice was collected from each subject over a period of 30 min, and the juice was preserved on ice to be used the next day. The duodenal juice obtained after CCK-B stimulation had the following characteristics: ph, 7.4 ± 0.4; osmolarity, 2BO mosmolll; protein content, <0.5 gil; bicarbonate concentration, 21 ± 3.3 meq/l; bile acid concentration, 1.7 ± 0.7 p.mol/ml ; and pancreatic trypsin concentration, 49 ± 9 U/ml. On the second day, gastrointestinal motility was recorded, and duodenal juice and blood samples were collected as described in part 1. After 2 h of equilibration and the occurrence of at least one interdigestive cycle, pancreatico-biliary juice containing PEG 4000 (5 gil) was perfused into the duodenum at 10 ml/min for 5 min, 30 min after a previous MMC. The duodenum was then again perfused with normal saline at the same rate for another 60 min. Blood samplings were performed, and duodenal juices were aspirated and pooled at 15-min intervals during the control period and at 5-min intervals after the beginning of the pancreatico-biliary juice perfusion. Analytical Methods The concentrations of trypsin, bile acid, and PEG 4000 were measured in all duodenal samples. Trypsin concentrations were determined by means of a titrimetric method using TAME (p-tosyl-t-arginine methylester HCl) as a substrate for enzyme activities (B). Bile acid (9) and PEG-4000 (10) were measured by spectrophotometric methods previously described. The enzyme and bile acid outputs were then expressed in kilounits (ku) per hour and micromoles per hour, respectively, based on recovery in relation to PEG-4000 (11). In all studies, the plasma was immediately separated by centrifugation and stored at - 20 C. The plasma PP concentrations were measured by a specific radioimmunoassay, which has been reported (12,13). Antiserum against PP (lot B -24B019) was used in a final dilution of 1: 1,250,000. Bovine PP (bpp) (lot 615-D63-1BB 9) was iodinated by the chloramine-t method (14). Highly purified human PP (lot B-200) was used as the standard in all assays. (All reagents were kindly donated by R. Chance, Eli Lilly & Co., Indianapolis, Ind.) Plasma was assayed at a final dilution of 1: 6. Separation was performed with a second antibody to rabbit immunoglobulin, and control tubes without first antibody were used to correct for nonspecific binding. The assay has a detection limit of 13 pg/ml of PP in plasma and is free of crossreactivity with gastric inhibitory polypeptide (GIP), vasoactive intestinal peptide (VIP), gastrin, cholecystokinin (CCK), secretin, glucagon, insulin, growth hormone, or somatostatin. The intraassay coefficient of variability was 3.9%, and the interassay coefficient was 9.1%. All samples from the same subject were assayed simultaneously. All results are expressed as mean ± SE. Coefficient of variation was calculated by the method previously described (15). Student's t-test for paired data was used for comparison. Significance was accepted at the 5% level. III AnI... w~l ~., J_ IV V'r~VII"~~"~~_"~' III IV Figure 2. Gastrointestinal motor activities in healthy subjects. Four characteristic phases of interdigestive motor complex recorded in the antrum, midduodenum, and proximal jejunum are shown.

4 January 1983 THE PANCREAS AND DUODENAL MOTILITY 13 Results Plasma Pancreatic Polypeptide Concentration, Pancreatico-Biliary Secretion, and Duodenal Motility In the 10 fasting healthy subjects, 30 interdigestive motor complexes were recorded, covering a total registration period of 87 h, 45 min. Four phases of duodenal motor activity were identified (Figure 2). Phase 1 was characterized by almost complete absence of spontaneous duodenal motor activity. Phase 2 was the period consisting of spontaneous :c- '<, ~ ~ c 'iii Q. >- ~ 10 i d J::. 800 Ji! ""- ~ ~..! iii 0 0 o irregular motor activity that usually ended abruptly with the appearance of bursts of rhythmic contractions of phase 3 (activity front) with pressure waves usually >30 mmhg and lasted for 4 ± 1.5 min. Phase 3 was followed by phase 4, a short period of <5 min, during which the motor activity returned to that seen during phase 1. Similar phasic motor activity could be identified in the antrum where phase 3 activity usually occurs during late phase 2 activity of the duodenum. The various phases could be quite easily identified on the tracings, and phase 3, which had the most striking features, was identified by the described criteria (16). The mean (±SE) duration of a complete cycle (between two episodes of phase 3 activity) was 87 ± 18 min. During duodenal phase 1, both luminal trypsin (5 ± 1 ku/h) and bile acid (72 ± 14 JLmollh) outputs were low but started to increase during early phase 2 and reached a maximum during late phase 2 (trypsin output = 36 ± 4 ku/h; bile acid output = 948 ± 268 JLmollh) (Figure 3). This continued into phase 3 and was followed by a rapid decline during phase 4, where the outputs of trypsin (8 ± 2 kuih) and bile acid (50 ± 10 JLmollh) were minimal (Figure 3). Plasma PP concentrations in the fasting subjects appeared to be associated with cyclic changes of pancreatico-biliary secretions (Figure 3). Low plasma PP concentrations (26 ± 4 pg/ml) were present during phase 1, and levels started to increase during phase 2 (108 ± 10 pg/ml) and reached a peak in late phase 2 and early phase 3 (143 ± 16 pg/ml). A rapid decline to low values (38 ± 6 pg/ml) occurred during phase 4. A representative profile of changes in trypsin and bile acid output, and plasma PP concentrations obtained from a healthy subject during 255 min of recording is shown in Figure 4. The peak pancreatic trypsin output preceded the occurrence of phase 3 activity and was accompanied by a marked increase in plasma PP concentrations. 150 E <,.!:!- '" 100 a- a- lii 50 E III III ii: 0 Phase Phase Phase Phase I II III IV Figure 3. Trypsin outputs (upper panel), bile acid outputs (middle panel), and plasma pancreatic polypeptide concentrations (lower panel) for each phase of duodenal motor activity. Results are expressed as mean ± SE. Asterisk indicates significant difference from values during phase 1 motor activity. Analysis of Fasting Plasma Pancreatic Polypeptide Concentrations The observed range of fasting plasma PP concentration in these 10 healthy subjects showed wide intra- and interindividual variations, ranging from 19 to 629 pg/ml (Table 1), when the mean plasma PP concentration was calculated without considering phasic changes of gastroduodenal motility. The mean coefficient of variation was 58% ± 6%. By contrast, the mean coefficient of variation of the mean plasma PP concentrations during phase 1 and 4 (15% ± 3%), phase 2 (24% ± 3%), and phase 3 (32% ± 6%) were significantly less (p < 0.01) than that of the overall coefficients of variations observed in these 10 subjects.

5 14 OWYANG ET AL. GASTROENTEROLOGY Vol. 84. No.1 40 Figure 4. Basal pancreatic trypsin output and plasma polypeptide concentrations observed over 240 min in a healthy volunteer. The start of phase 3 in the upper duodenum is indicated by arrows. Note that each cycle interval for this subject was -70 min. Peak pancreatic trypsin output was always accompanied by a simultaneous increase in plasma pancreatic polypeptide concentration. Solid line indicates plasma PP. Broken line indicates trypsin output d c.~ ~ 10, i i i i i i i J Minutes 140 E ~ a. 80 a. ca E tij ca Z5: 20 Effect of Pancreatico-Biliary Juice on Plasma Pancreatic Polypeptide Concentration Perfusion of the duodenum with pancreaticobiliary juice 30 min after a previous phase 3 activity stimulated the release of PP into the circulation. The plasma PP concentration started to increase within 5 min from a basal level of 51 ± 8.9 pg/ml, reaching a peak of 166 ± 22 pg/ml at 10 min, and returned to basal at 30 min after infusion of pancreatico-biliary juice (Figure 5). The trypsin and bile acid outputs were 6 ± 2.5 ku/h and 110 ± 14 p,mollh, respectively, before perfusion of pancreatico-biliary juice. These increased to a peak level of 42 ± 4.7 ku/h and 1210 ± 311 p,mollh, respectively, after perfusion of the duodenum with pancreatico-biliary juice. Based on the concentrations of trypsin and bile acid in the pancreatico-biliary juice, which was perfused into the duodenum at 10 ml/min, these measured pancreatic and biliary outputs were mainly coming from infusion of the duodenal juice. Discussion The results of our study clearly indicated that cyclic fluctuations of plasma PP concentrations occurred in fasting humans, and that these changes appeared to be associated with a cyclic in~reas~ ~f pancreatic and biliary secretions and phasic activities of the interdigestive motor complex of the duodenum. A marked increase in plasma PP concentrations occurred during late phase 2 and reached a peak level in early phase 3. Similar observations have been made in dogs (3,17) and more recently in humans (18,19). In the study by Janssens et al. (19), the peak plasma PP concentration occurred during late phase 2 activity and was followed by decline in plasma levels during phase 3 activity. In our study, we observed a decline in plasma PP concentration during late phase 3. Hence, the apparent difference between the two studies is probably due to different blood sampling intervals. Plasma levels of gastrointestinal hormones such as gastrin, cholecystokinin, and secretin appear to be quite stable during fasting (20). Oscillations of plasma insulin (21), glucagon (21), and somatostatin (22) have been shown to occur in monkeys. These appear to have a short period of 6-8 min similar to that observed in the isolated canine pancreas (23). Hansen et al. (22) did report an additional oscillating period of min for somatostatin in monkeys and Aizawa et al. (24) reported that the plasma somatostatin level fluctuated in phase with gastric Table 1. Fasting Plasma Pancreatic Polypeptide Concentrations Observed During Three Interdigestive Motor Complexes in 10 Subjects Subject Fasting plasma concentrations Mean ± SD (pg/ml) 135 ± ± ± ± ± ± ± ± ± ± 8 Range (pg/ml)

6 January 1983 THE PANCREAS AND DUODENAL MOTILITY 15 *..., ~!: 100 a. a.. Ė ii: t P-B juice Figure 5. Plasma pancreatic polypeptide concentration in response to intraduodenal perfusion with pancreatico-biliary (P-B) juice at 10 ml/min for 5 min. Asterisk denotes points significantly greater than basal, where the duodenum was perfused with normal saline o Minutes interdigestive contractions in dogs. However, this phenomenon has not been observed in humans. In humans, the only other gastrointestinal hormone known to change cyclically with phasic intestinal motor activity during fasting is motilin (20,25,26). In this study, we also observed that plasma motilin levels showed a characteristic fluctuation through the interdigestive cycle with maximum levels occurring during late phase 2 and early phase 3 activities (the results on motilin levels will be reported fully elsewhere). Similar to motilin (26), plasma PP concentration during fasting revealed a wide intraindividual variation. The largest variation was observed in subject 7 whose plasma PP concentration fluctuated from a low of 92 pg/ml during phase 1 to a high of 629 pg/ml during phase 3. However, much smaller variations were observed when plasma PP concentrations were calculated in accordance with the different phases of the intestinal MMC. This observation suggests that erroneously high basal concentration may result if only a single basal blood sample were obtained. This possibility should be taken into consideration when designing experiments involving studies of endogenous release of PP. The mechanism responsible for the cyclic fluctuation of plasma PP during the interdigestive state is unknown. Schwartz et al. (27) demonstrated that fluctuations of PP concentrations and basal acid output in humans are correlated. However, acidification of the duodenum only inconsistently induces a small increase in plasma PP (12). It has not been shown to induce typical MMC in humans (28). Our observation that bursts of increased pancreatic and biliary secretion into the duodenum during late phase 2 and early phase 3 duodenal motor activity were associated with an increase in plasma PP concentrations suggested that these events may be causally related. This contention is further supported by the demonstration that perfusion of the duodenum with pancreatico-biliary juice stimulated the release of PP into the circulation. The increase in plasma PP after pancreatico-biliary perfusion is unlikely to be due to spontaneous cyclic increase in plasma PP levels, because it occurred within 5-10 min after infusion of the juice and 35 min after the previous period of phase 3 activity, whereas the mean periodicity of spontaneous PP oscillations was -90 min. We perfused the duodenum for only 5 min to simulate physiologic phasic pancreatico-biliary secretion, and the pancreatic enzyme and bile acid outputs achieved were similar to those observed during phase 3 activity. Furthermore, the increases in plasma PP levels after duodenal perfusion were also similar to those occurring during late phase 2 and phase 3 activity. These observations suggest that phasic pancreatico-biliary secretion may be responsible for the cyclic fluctuation of plasma PP during the interdigestive period. The mechanism by which pancreatico-biliary juice in the duodenum stimulates the release of plasma PP is also unknown. There is considerable evidence for cholinergic regulation of PP secretion (29). Recently, Greenberg et al. (17) demonstrated that vagal blockade abolished cyclic fluctuations of plasma PP concentrations in fasted dogs. Therefore, it is conceivable that pancreatico-biliary juice in the duodenum may generate a cholinergic enteropancreatic reflex to stimulate PP release. However, a hormonal mechanism whose release is cholinergi-

7 16 OWYANG ET AL. GASTROENTEROLOGY Vol. 84. No. 1 cally dependent could not be ruled out. We have shown that pancreatico-biliary juice in the duodenum also stimulates motilin secretion in humans (30). It has been demonstrated that infusion of motilin not only elicits an activity front but also induces a peak in plasma PP (19). Therefore, it is also possible that pancreatico-biliary juice in the duodenum releases motilin, which in turn stimulates PP secretion. Further studies are needed to elucidate the exact nature of the enteric signal generated by the pancreatico-biliary juice. Also unclear is the factor(s) in the pancreaticobiliary juice that stimulates the release of plasma PP. Perfusion of the duodenum with normal saline of similar ph and osmolarity to the pancreatico-biliary juice did not alter the basal plasma PP concentration. Therefore, neither the ph nor osmolarity of the juice could account for the response. Protein is a potent stimulus for PP release (31), but the protein content in the juice was low and much less than that required to elicit a PP response (31). It has been proposed that one of the functions of the secretory and motor events of the interdigestive MMC is to serve as an "intestinal housekeeper," cleaning up the intestine in between meals (32). Pancreatic enzyme output during phase 3 motor activity is similar to thatobserved after a meal and is sufficient to digest food remnants or cellular debris in the gastrointestinal tract (33). The mechanisms regulating these cyclic secretory and motor events have not been fully elucidated. Intravenous infusion of motilin can initiate the interdigestive motor complex (34) and its plasma concentration rises in association with duodenal phase 3 activity (20,25,26). Infusion of PP, on the other hand, neither induces a MMC nor prevents its occurrence (19). The only apparent physiologic action of PP in humans is inhibition of pancreatic and biliary secretion (35). Therefore, the phasic release of PP into the circulation after peak pancreatic biliary secretions may be responsible for the marked suppression of pancreatic enzyme andbile acid outputs observed during phase 4. These observations support the hypothesis that there is a feedback loop whereby pancreatico-biliary secretions stimulate the release of PP, which in turn inhibits pancreatic and biliary secretion. This enteropancreatic-pp axis, therefore, provides an important autoregulatory mechanism for the proper functioning of the pancreas in digestion. References 1. Boldyreff W. Einigeneui seiten der tatigheit des pankreas Der ubeitritt des pancreossaftes und anderer darnsekrete in den magen. Die Physiologische und klinische Badentung dieser Etocheisnung. Eigebn PhysioI1911;11: Dimagno EP, Hendricks JC, Go VLW, et al. Relationships among canine fasting pancreatic and biliary secretions, pancreatic duct pressure and duodenal phase III motor activity Boldyreff revisited. Dig Dis Sci 1979;24: Keane FC, DiMagno ER, Dozois RR, Go VLW. Relationships among canine interdigestive exocrine pancreatic and biliary flow, duodenal motor activity, plasma pancreatic polypeptide, and motilin. Gastroenterology 1980;78: Vantrappen GR, Peeters TL, Janssens J. The secretory component of the interdigestive migrating motor complex in man. Scand J Gastroenterol 1979;14: Larsson LI, Sundler F, Hakanson R. Pancreatic polypeptide: a postulated new hormone: identification of its cellular storage site by light and electron microscopic immunocytochemistry. Diabetologia 1976;12: Owyang C, Scarpello JM, Vinik AI. Correlation between pancreatic enzyme secretion and plasma concentration of human pancreatic polypeptide in health and in chronic pancreatitis. Gastroenterology 1982;83: Malagelada JR, Rees WDW, Mazzotta LJ, et al. Gastric motor abnormalities in diabetic and postvagotomy gastroparesis: effect of metoclopramide and bethanechol. Gastroenterology 1980;78: Pelot D, Grossman MI. Distribution and fate of pancreatic enzymes in small intestine of the rat. Am J Physiol 1962; 202: Talalay P. Enzymic analysis of steroid hormones. Methods Biochem Anal 1960;8: Hyden S. A turbidimetric method for the determination of higher polyethylene glycols in biological materials. K Lantbrukshogsk Ann 1956;22: Go VLW, Hofmann AF, Summerskill WHJ. Simultaneous measurements of total pancreatic and biliary and gastric outputs in man using a perfusion technique. Gastroenterology 1970;58: Floyd JC, Fajans SS, Pek S, et al. A newly recognized pancreatic polypeptide; plasma levels in health and disease. Recent Prog Horm Res 1977;33: Glaser B, Vinik AI, Sive AA, et al. Plasma human pancreatic polypeptide response to administered secretion: effects of surgical vagotomy, cholinergic blockage and chronic pancreatitis. J Clin Endocrinol Metab 1980;50: Hunter WM, Greenwood FC. Preparation of iodine 131 labelled human growth hormone of high specific activity. Nature (Lond) 1962;194: Colton T. Statistics in medicine. Boston: Little, Brown & Co. 1974: Vantrappen G, Janssens J, Hellemans J, et al. The interdigestive motor complex of normal subjects and patients with bacterial overgrowth of the small intestine. J Clin Invest 1977;59: Greenberg GR, Hall KE, Mui H, et al. Pancreatic polypeptide and migrating motor complexes in the dog: effect of vagal blockage (abstr). Regul Pept 1980:1(Suppl.):S Lux G, Femppel J, Lederer P, et al. Pancreatic polypeptide, motilin, and somatostatin levels during interdigestive motility in man (abstr). Gastroenterology 1980;78: Janssens J, Hellemans J, Adrian TE, et al. Pancreatic polypeptide is not involved in the regulation of the migrating motor complex in man. Regul Pept 1982;3: Rees WDW, Malagelada JR, Go VLW. Gastrointestinal hormone patterns associated with interdigestive and postprandial motor activity in human proximal bowel. (abstr). Gut 1978;19:A Goodner C], Walike BC, Koerker DJ, et al. Insulin, glucagon and glucose exhibit synchronous, sustained oscillations in fasting monkeys (Macaca mulatta). Science 1977;195: Hansen BC, Vinik AI, [en KLC, et al. Circulating somatostatin

8 January 1983 THE PANCREAS AND DUODENAL MOTILITY 17 in monkeys: fluctuations in basal levels and effects of forced overfeeding and food deprivation. Am J Physiol 1982;(in press). 23. Stagner JI, Samols E, Weir GC. Sustained oscillations of insulin, glucagon, and somatostatin from the isolated canine pancreas during exposure to a constant glucose concentration. J Clin Invest 1980;65: Aizawa I, Itoh Z, Harris V, et al. Plasma somatostatin-like immunoreactivity during the interdigestive period in the dog. J Clin Invest 1981;68: Peeters TL, Vantrappen G, Janssens J. Fasting plasma motilin levels are related to the interdigestive motility complex. Gastroenterology 1980;79: You CH, Chey WY, Lee KY. Studies on plasma motilin concentration and interdigestive motility of the duodenum in humans. Gastroenterology 1980;79: Schwartz TW, Stenquist B, Olbe L, et al. Synchronous oscillations in the basal secretion of pancreatic polypeptide and gastric acid. Depression by cholinergic blockade of pancreatic polypeptide concentrations in plasma. Gastroenterology 1979; 76: Lewis TD, Collins SM, Fox JE, et al. Initiation of duodenal acid-induced motor complexes. Gastroenterology 1979; 77: Schwartz TW, Holst JJ, Fahrenkrug J, et al. Vagal cholinergic regulation of pancreatic polypeptide secretion. J Clin Invest 1979;61: Owyang C, Funakoshi A, Vinik AI. Modulation of plasma motilin concentration by pancreatico-biliary juice (abstr). Clin Res 1981;29:713A. 31. Scarpello JH, Vinik AI, Owyang C. The intestinal phase of pancreatic polypeptide release. Gastroenterology 1982; 82: Code CF, Schlegel JF. The gastrointestinal interdigestive housekeeper: motor correlates of the interdigestive myoelectric complex of the dog. In: Daniel EE, ed., Proceedings of the Fourth International Symposium on Gastrointestinal Motility. Vancouver, British Columbia: Mitchell Press, 1973: Malagelada JR, Go VLW, Summerskill WHJ. Different gastric, pancreatic and biliary responses to solid-liquid or homogenized meals. Dig Dis Sci 1979;24: Vantrappen G, Janssens J, Peeters TL, et al. Motilin and the interdigestive migrating motor complex in man. Am J Dig Dis 1979;24: Greenberg GR, McCloy RF, Chadwick VS, et al. Effect of bovine pancreatic polypeptide on basal pancreatic and biliary outputs in man. Am J Dig Dis 1979;24:11-4.