Pancreatobiliary responses to an intragastric amino acid meal: comparison to albumin, dextrose, and a maximal cholecystokinin stimulus

Measurement of gallbladder motor functions: an overview

Control of gallbladder motor functions involve a constant interplay between several stimulatory and inhibitory hormones and neurotransmitters. Gallbladder response to a stimulus is complicated involving rapid alternation of emptying and refilling during the postprandial period. Conventional methodology is not capable of evaluating both emptying and refilling in a quantitative manner, and hence previous studies have yielded a large variation in results in health and conflicting results in gallstone patients. There is therefore, a need for improved methodology. Postprandial refilling and turnover of bile are important parameters that need to be assessed when addressing gallbladder motor function and its role in the pathogenesis of cholesterol gallstone disease.

Persistent decreased plasma cholecystokinin levels in celiac patients under gluten-free diet: respective roles of histological changes and nutrient hydrolysis

Celiac disease is associated with impaired cholecystokinin (CCK) release. The mechanism by which CCK release is impaired is poorly understood and seems to be related to the mucosal atrophy or to decreased stimulation due to reduced intraduodenal nutrient hydrolysis. The aims of our study were to evaluate basal and postprandial CCK in celiac patients presenting with distinctive types of mucosal lesions (normal, infiltrative and atrophic), and to study the role of protein hydrolysis on CCK release. Plasma CCK was measured in 20 celiac patients (normal mucosa: n=6; infiltrative type: n=6; atrophic type=8) and 9 controls, before and after ingestion of a polymeric or a semi-elemental meal. Significant decreases in basal CCK plasma (B 0.6 [95% CI, 0.3-1.3] pmol/l; p<0.003) and postprandial CCK area under curve (AUC 34 [19-61] pmol/l x 120 min, p<0.0001) were observed in patients with an atrophic mucosa compared with treated patients (B 1.6 [1.0-2.4] pmol/l, AUC 267 [172-414] pmol/l x 120 min) or healthy volunteers (B 1.0 [0.7-1.4] pmol/l, AUC 186 [131-264] pmol/l x 120 min). A significant defective CCK release was also observed in patients with an infiltrative type: B 0.4 [0.2-0.7] pmol/l and AUC 56 [31-101] pmol/l x 120 min; p<0.0001. Administration of a semi-elemental diet did not correct the defective CCK release. In conclusion, the decreased CCK levels observed in celiac patients are not strictly related to the mucosal atrophy but rather to the lymphocytic infiltrate. Administration of a predigested meal did not correct the impaired CCK release. Some inhibitory mechanism could be involved in the CCK cell dysfunction observed in celiac patients presenting with lesser degrees of disease activity.

Regulation of the action of the novel cholecystokinin-releasing peptide diazepam binding inhibitor by inhibitory hormones and taurocholate

Diazepam binding inhibitor (DBI1-86) has recently been isolated in search for a cholecystokinin (CCK)-releasing peptide in the duodenum that is responsible for the feedback regulation of exocrine pancreatic secretion. Synthetic porcine DBI1-86 stimulates CCK release in vivo and in vitro from isolated intestinal mucosal cells. We postulated that DBI intraduodenally releases CCK in a paracrine fashion and might be the missing link in the feedback regulation of exocrine pancreatic secretion. Somatostatin, peptide YY (PYY) and taurocholate are known to inhibit feedback-stimulated CCK release in the rat. In this study, we investigated the effect of somatostatin, PYY and taurocholate on DBI-stimulated CCK secretion. Dispersed rat intestinal mucosal cells were prepared from the proximal small bowel and continuously perfused. The perfusate was collected and the release of CCK into the medium was measured. DBI1-86 dose-dependently stimulated CCK release, with a maximal effect at 10(-9) M. Somatostatin blocked the DBI-stimulated CCK release. Pretreatment of the cells with pertussis toxin fully reversed the inhibitory effect of somatostatin on DBI-stimulated CCK secretion, suggesting that somatostatin exerts its action by an inhibitory G-protein. In contrast, PYY (10(-6) M) and taurocholate (10(-6) M) did not affect DBI stimulated CCK levels, indicating that they act through different mechanisms to inhibit feedback-stimulated CCK release.

Nutrients and cyclical interdigestive pancreatic enzyme secretion in humans

BACKGROUND AND AIMS

It is hypothesised that nutrients increase pancreatic enzyme secretion by converting cyclical interdigestive secretion to a non-cyclical pattern. This study tested the hypotheses that nutrients do not interrupt cycles and determined the relation of nutrients, calories, and osmotic load to the rate of pancreatic secretion.

METHODS

Twenty six healthy persons were intubated with oroduodenal and orogastric tubes. Each had one of four different solutions containing 12 to 36% of calories as protein, 24 to 48% as fat, and 40 to 64% as carbohydrate infused into the duodenum at 40, 90, or 160 kcal/h for 300 minutes. Nine g/l sodium chloride (290 mOsm) was added to 16 infusates; osmolality of the other 10 infusates was 24 to 98 mOsm. Pancreatic enzyme outputs were measured every 15 minutes and peaks of enzyme secretion were identified.

RESULTS

The number of enzyme peaks was similar for the different infusates and the proportion of nutrients in the infusates did not affect secretion of individual enzymes. The nadir, but not the peak of the cycles of enzyme outputs correlated with increasing the caloric load (r = 0.55, p < 0.003 for nadir:peak ratio). Increasing osmolality did not affect cycling but reduced (p < 0.001) enzyme output.

CONCLUSION

Nutrients entering the duodenum do not abolish cycles of enzyme secretion; instead they modulate cycles by increasing the nadir. Forty and 90 kcal infusions submaximally stimulate pancreatic secretion and might be used in patients with pancreatitis without producing pain; adding sodium chloride to solutions should increase this effect.

Gastric emptying and release of incretin hormones after glucose ingestion in humans

This study investigated in eight healthy male volunteers (a) the gastric emptying pattern of 50 and 100 grams of glucose; (b) its relation to the phase of interdigestive motility (phase I or II) existing when glucose was ingested; and (c) the interplay between gastric emptying or duodenal perfusion of glucose (1.1 and 2.2 kcal/min; identical total glucose loads as orally given) and release of glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1(7-36)amide (GLP-1), C-peptide, insulin, and plasma glucose. The phase of interdigestive motility existing at the time of glucose ingestion did not affect gastric emptying or any metabolic parameter. Gastric emptying of glucose displayed a power exponential pattern with a short initial lag period. Duodenal delivery of glucose was not constant but exponentially declined over time. Increasing the glucose load reduced the rate of gastric emptying by 27.5% (P < 0.05) but increased the fractional duodenal delivery of glucose. Both glucose loads induced a fed motor pattern which was terminated by an antral phase III when approximately 95% of the meal had emptied. Plasma GLP-1 rose from basal levels of approximately 1 pmol/liter of peaks of 3.2 +/- 0.6 pmol/liter with 50 grams of glucose and of 7.2 +/- 1.6 pmol/liter with 100 grams of glucose. These peaks occurred 20 min after glucose intake irrespective of the load. A duodenal delivery of glucose exceeding 1.4 kcal/min was required to maintain GLP-1 release in contrast to ongoing GIP release with negligibly low emptying of glucose. Oral administration of glucose yielded higher GLP-1 and insulin releases but an equal GIP release compared with the isocaloric duodenal perfusion. We conclude that (a) gastric emptying of glucose displays a power exponential pattern with duodenal delivery exponentially declining over time and (b) a threshold rate of gastric emptying of glucose must be exceeded to release GLP-1, whereas GIP release is not controlled by gastric emptying.

Gallbladder motility, gallstones, and the surgeon

Cholecystectomy is one of the commonest surgical procedures in the Western world, with more than half a million procedures performed annually in the United States alone. In recent years, studies of gallstone pathogenesis and gallbladder disease have increasingly focused on abnormal gallbladder motility in the pathogenesis of some, if not all, gallbladder conditions. The control of gallbladder motility is complex and depends on an intricate interplay of neural and hormonal factors. An understanding of the control of gallbladder motility is crucial to the understanding of the mechanisms of gallstone formation and may help to explain the failure to cure symptoms after cholecystectomy in up to one third of patients. The purpose of this article is to outline mechanisms controlling gallbladder motility, examine recent developments in our understanding of this complex process, and relate changes in motility to common disease conditions of the gallbladder. The role of altered motility in the pathogenesis of gallstones is discussed and the effects of commonly performed surgical procedures such as truncal vagotomy and cholecystectomy on upper gut physiology are reviewed.

Rat pancreatic secretory response to intraduodenal infusion of elemental vs polymeric defined-formula diet

Pancreatic protein and fluid secretion in response to intraduodenal infusion of polymeric and elemental liquid defined-formula diets were studied in conscious rats. Rats were prepared with chronic pancreatic, biliary, and duodenal cannulas and had their pancreatic secretions collected and continuously returned to the intestine during intraduodenal infusion with commercial liquid defined-formula diets. Ensure HN, a polymeric defined-formula diet containing intact protein, and two elemental diets, in which the protein component consisted of enzymatically hydrolyzed protein and free amino acids, were tested. Ensure HN strongly stimulated pancreatic protein and fluid secretion, causing a maximal 10-fold increase in protein secretion. In contrast, the elemental diets stimulated only 30% to 47% of the protein secretion caused by Ensure HN. Separate infusion of the fat, protein, and carbohydrate components of one elemental diet, RTF Elemental, showed that fat was the major stimulant, but the responses to the separate components were not significantly different from each other and none caused more than 50% of the response to the complete diet. The results demonstrate that defined-formula elemental diets are much less stimulatory for pancreatic enzyme secretion than defined-formula polymeric diets in rats. The probable explanation for this difference is the replacement of intact protein by hydrolyzed protein and amino acids in the elemental diets.

Relation between gastric emptying of albumin-dextrose meals and cholecystokinin release in man

The effect of intragastric dextrose on albumin-stimulated cholecystokinin (CCK) release was studied in five healthy subjects and was related to gastric emptying and pancreatobiliary secretions. When combined with low concentrations of dextrose (4 g/100 ml), a 500-ml solution of albumin (7 g/100 ml) was rapidly emptied from the stomach into the duodenum (T1/2: 35 min). This rapid gastric emptying resulted in an only transient stimulation of pancreatobiliary secretion and an integrated CCK release of 278 +/- 45 pM x 180 min. When the concentration of dextrose in the albumin solution was increased from 4 g/100 ml to 21 g/100 ml, gastric emptying rate was distinctly slower (T1/2: 78 min; P < 0.01) and pancreatobiliary secretions became sustained (P < 0.01). CCK release was markedly higher (900 +/- 421 pM x 180 min; P < 0.05) after ingestion of the solution containing a high dextrose concentration. Intraduodenal infusion of 21 g/100 ml dextrose (3.1 ml/min) failed to significantly stimulate plasma CCK levels (119 +/- 38 pM x 120 min). We suggest that the higher CCK release in response to intragastrically administered albumin solution containing high concentrations of dextrose may have been induced by augmented peptic digestion of albumin due to delayed gastric emptying and by increased enteral digestion of albumin due to increased pancreatobiliary outputs.

Plasma concentrations of regulatory peptides in obseity following modified sham feeding (MSF) and a liquid test meal

Plasma concentrations of regulatory peptides were monitored in groups of obese and normal-weight subjects following modified sham feeding and a liquid fatty meal. Following modified sham feeding a significant increase in immunoreactive cholecystokinin (CCK) in plasma was recorded in both groups. In the obese subjects, however, the concentrations following sham feeding were significantly lower than in normal-weight subjects, and the initial part of the response was negative. Basal and modified sham feeding stimulated immunoreactive pancreatic polypeptide (PP) concentrations in plasma did not differ between the groups. After the liquid fatty meal plasma CCK concentrations increased similarly in both groups. In contrast immunoreactive neurotensin and somatostatin concentrations following the meal were lower in the obese group, and a changed concentration-time pattern for somatostatin was observed in the obese group. Postprandial concentrations of PP and immunoreactive gastrin were not different in the groups. The results indicate that the plasma concentration patterns of CCK, somatostatin and NT are disarranged in obesity. The changes may promote rapid propulsion and absorption of ingested food, and facilitate deposition of fat in adipose tissue in obesity and thus may be of pathophysiological importance.

A decade of experiences with radioimmunoassays for cholecystokinin in The Netherlands

The radioimmunologic determination of cholecystokinin (CCK) has proved to be notoriously difficult. This is due to the specificity of antibodies, preparation of radiolabeled CCK and low CCK concentrations in human plasma. About 10 years ago we succeeded in developing two highly sensitive region-specific radioimmunoassays for CCK. Antibody T204 binds to the sulfated tyrosine region of CCK, while antibody 1703 reacts with biologically active molecular forms of CCK containing at least 14 amino acid residues. Both antibodies are devoid of significant cross-reaction with gastrin. By means of these two radio-immunoassays CCK concentrations were measured in both tissue and plasma of various species, including man. In addition, the molecular forms of CCK in tissue and plasma were characterized. These CCK assays were used to study the mechanism of CCK secretion. It appeared that digested rather than intact protein and fat stimulated CCK release from the small intestine. The physiologic and pathophysiologic role of CCK in humans was studied using CCK radioimmunoassays and specific CCK-receptor antagonists. CCK was found to play an important role in pancreatic enzyme secretion, gallbladder contraction, and gastrointestinal motility but possibly also in pancreatic carcinogenesis and regulation of satiety and satiation.

Are energy and energy-providing nutrients related to exocrine carcinoma of the pancreas?

During 1984-88 a population-based case-control study was carried out in The Netherlands in collaboration with the International Agency for Research on Cancer in order to further explore the possible relationship between diet and exocrine pancreatic carcinoma. Past habitual dietary intake was assessed in 164 cases and 480 controls. This is the first series of population-based studies of pancreas cancer to perform a comprehensive assessment of diet. The results of logistic regression analysis, controlled for age, gender and total cigarette consumption, suggested a positive association with past habitual intake of energy in directly interviewed patients (OR highest versus lowest quintile 3.35; 95% confidence interval 1.51-7.18). No indication of an effect of Quetelet index was found. When maximum-weight-ever-achieved was used, nonsignificantly reduced risks were observed for the upper 4 quintiles of "maximum" Quetelet index. After controlling for age, gender, response status and total cigarette consumption, a positive relationship with habitual past intake of total carbohydrates was observed (OR 2.40; 95% confidence interval 1.44-3.99). The effect decreased considerably when the analysis was restricted to subjects who reported stable long-term dietary intake. After controlling for age, gender, total cigarette consumption and response status, a significant, positive association between pancreatic cancer and past habitual intake of simple sugars was found (OR 1.95; 95% confidence interval 1.24-3.07). Among those who reported stable long-term dietary intake, no effect was seen. The positive effect of simple sugars was present in males only (OR 2.15; 95% confidence interval 1.18-3.93) and was smaller in men who reported long-term stable dietary intake. Our findings suggest that the development of exocrine pancreatic carcinoma is positively related to past habitual intake of total energy, total carbohydrates and simple sugars, whereas no relationship with body-mass index was observed.