Regulation of pancreatic endocrine function by cholecystokinin: studies with MK-329, a nonpeptide cholecystokinin receptor antagonist

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

Negative control of human pancreatic secretion: physiological mechanisms and factors

The negative control of pancreatic exocrine secretion in man occurs during the interdigestive and postprandial periods of the digestive cycle. The physiological mechanisms involved include negative feedback mechanisms, well described and accepted in animals, and controlled by the cholecystokinin- and secretin-releasing factors of pancreatic and duodenal origin, along with the active pancreatic proteases present in the upper gut. The presence of these factors and their efficacy in humans, however, have their supporters and detractors, with a possibility for reconciliation among opponents. Besides these releasing factors, hormones, mostly from the intestine, are also involved in this inhibitory process of pancreatic secretion. Somatostatin, peptide YY, pancreatic polypeptide, glucagon, ghrelin, and leptin were described as potentially involved from studies mostly performed on animals. Finally, bile and bile salts have mixed responses on this inhibition, and their effects seem to be at the intestine level with gastrointestinal hormones involved. Future studies will have to be performed in humans to determine the presence of cholecystokinin- and secretin-releasing factors and their role. Finally, the demonstrated modulatory action of hormones and bile acids in other species needs to be confirmed in humans.

Lack of relationship between blood glucose-lowering activity of colestimide and serum cholecystokinin (CCK) concentrations in patients with type 2 diabetes

Colestimide has been reported to lower blood glucose levels in patients with type 2 diabetes and hypercholesterolemia. We investigated the mechanism of the hypoglycemic activity of colestimide by examining changes in serum cholecystokinin (CCK) and insulin concentrations before and after its 2-week oral administration. A total of seven type 2 diabetes inpatients with hypercholesterolemia received colestimide after their blood glucose levels had stabilized. We daily measured plasma glucose levels and serum lipid concentrations, calculated Body Mass Index (BMI), and determined whole-day changes in serum immunoreactive insulin (IRI) and CCK concentrations in all study subjects. We daily measured plasma glucose levels, as well as serum IRI and CCK concentrations at 10 time points for measurement. Plasma glucose levels, as well as serum IRI and CCK concentrations before and after the 2-week oral administration of colestimide were compared. The means of total cholesterol levels and BMI decreased significantly after administration. At time points for measurement (10 : 00 and 12 : 00), plasma glucose levels decreased significantly after administration (P=0.026 and P=0.009, respectively). Diurnal changes in serum IRI and CCK concentrations were not observed after administration, except for the IRI concentration at 20: 00. The effect of colestimide on CCK may not explain the mechanism of its blood glucose-lowering activity in patients with type 2 diabetes and hypercholesterolemia.

Characterization of mice lacking the gene for cholecystokinin

CCK acts peripherally as a satiating peptide released during meals in response to lipid feeding and centrally functions in the modulation of feeding, exploratory, and memory activities. The present study determined metabolic parameters, food intake, anxiety-like behaviors, and cognitive function in mice lacking the CCK gene. We studied intestinal fat absorption, body composition, and food intake of CCK knockout (CCK-KO) mice by using the noninvasive measurement of intestinal fat absorption along with quantitative magnetic resonance (QMR) imaging and the DietMax system, respectively. Additionally, exploratory and memory capacities were assessed by monitoring running wheel activity and conducting elevated plus-maze and Morris water-maze tests with these mice. Compared with wild-type (WT) littermate controls, CCK-KO mice had normal food intake, fat absorption, body weight, and body mass. CCK-KO mice ate more food than control animals during the light period and less food during the dark period. Energy expenditure was unchanged between the genotypes; however, CCK-KO mice displayed greater fatty acid oxidation. CCK-KO mice were as active as WT animals in the running wheel test. CCK-KO mice spent more time in the closed arms of an elevated plus-maze, indicative of increased anxiety. Additionally, CCK-KO mice exhibited attenuated performance in a passive avoidance task and impaired spatial memory in the Morris water maze test. We conclude that CCK is involved in metabolic rate and is important for memory and exploration. CCK is intimately involved in multiple processes related to cognitive function and food intake regulation.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.

Entero-insular axis in children with anorexia nervosa

Entero-insular axis plays an important role in generating satiety signal. Thus disturbances in this axis may influence the course of anorexia nervosa. The aim of the study was analysis of the function of the hormonal part of the entero-insular axis in girls with anorexia nervosa. Thirteen girls with anorexia nervosa and in 10 healthy girls were studied. Each girl was subjected to oral glucose tolerance test and standard meal test. Blood was collected before stimulation and within 15, 30, 60, and 120 min thereafter. The concentrations of all peptides were determined by radioimmunoassay commercial kits. Fasted and postprandial levels of these peptides as well as integrated outputs were measured. Fasting insulin concentration was significantly higher in the group of girls with anorexia nervosa than in the control group (p<0.03). What more in girls with anorexia the integrated output of insulin was significantly lower in oral glucose tolerance test than after the meal (p<0.001). Also the integrated output of glucagon in both tests was higher in the group of girls with anorexia than in the control group. The mean output of pancreatic polypeptide and cholecystokinin in anorexia group was significantly higher (p<0.001 in both cases) than that in the control group but only after the test meal. The integrated outputs of gastric inhibitory peptide in both tests were significantly higher in anorectic girls than those in the control group (oral glucose tolerance test, p<0.02; meal test, p<0.001), However, mean values of the integrated output of glucagon-like peptide 1 in both tests were significantly higher in the control group than in the girls with anorexia (p<0.001 in each case). Highly significant correlation was found between glucose concentration and the concentrations of insulin, cholecystokinin, and gastric inhibitory peptide in both tests and for the both groups. In the anorectic girls, significant correlation between insulin concentration and the concentration of gastric inhibitory peptide was found after both stimulation tests and between insulin and cholecystokinin after oral glucose only.

CONCLUSION

the disturbed secretion of the hormones of entero-insular axis after the meal in anorectic girls may have negative influence on the course of anorexia nervosa. This disease has no effect on the incretin function of cholecystokinin, gastric inhibitory peptide and glucagon-like peptide 1.

Localization of cholecystokinin receptor subtypes in the endocine pancreas

This study was undertaken to clarify the controversy in the literature about pancreatic localization of the cholecystokinin (CCK) CCK(A) and CCK(B) receptors. With antibodies used by other investigators, we first established their specificity by Western blotting, indirect immunofluorescence, and confocal microscopy with each antibody's peptide antigen. Co-localization assays between the CCK receptors and the pancreatic hormones insulin, glucagon, and somatostatin revealed that the CCK(A) RAbs 1122 and R1-2 recognized insulin and glucagon cells in rat, pig, and human pancreas but not in the somatostatin cells. Conversely, the three CCK(B) RAbs tested, 9262, 9491, and GR4, identified the somatostatin cells. Abs 9491 and GR4 occasionally co-localized with glucagon, a feature that never occurred with Ab 9262. Finally, the specificity of Ab 9262 for the pancreatic CCK(B) R was confirmed in six different species. It co-localized with somatostatin but never with glucagon in these species. Our data suggest the use of Abs 1122 and 9262 to specifically identify and localize pancreatic CCK(A) and CCK(B) receptors, respectively. Confusion in the literature may result from the lack of specificity of most antibodies used, as established in this study.

Effect of cholecystokinin-A receptor blockade on postprandial insulinaemia and gastric emptying in humans

Our aim was determine the relationship between cholecystokinin (CCK)-A receptor blockade, glucose levels, insulin secretion and gastric emptying in humans, and to assess the effect of CCK-A blockade on pancreatic polypeptide secretion. After a 12-h fast, six healthy volunteers were given [99mTc]iminodiacetic acid monosodium salt (IDA) intravenously (5 mCi). One hour later they were offered a 577 kcal liquid meal containing [99mTc]diethylenetriaminepentaacetic acid (DTPA) (2 mCi) and glucose (105 g). Scintigraphic gastric and gallbladder activity, and plasma glucose, insulin and pancreatic polypeptide responses were monitored. In a second experiment, a continuous intravenous infusion of loxiglumide (7.5 mg kg h(-1)) was started 60 min before and continued until 120 min after test meal ingestion to block the CCK-A receptors. Gallbladder emptying was blocked by loxiglumide. Loxiglumide accelerated gastric emptying, increased insulin secretion without alteration of glucose profiles, and abolished all phases of the postprandial pancreatic polypeptide response. Blockade of peripheral CCK-A receptors accelerates gastric emptying of liquids with an increase in postprandial insulin levels. The lack of changes in glycaemia suggests that alternative homeostatic mechanisms also control postprandial glucose levels. Inhibition of pancreatic polypeptide release may reflect an independent effect of loxiglumide on vagal control involved in pancreatic polypeptide release.

Genetic, pharmacological and functional analysis of cholecystokinin-1 and cholecystokinin-2 receptor polymorphism in type 2 diabetes and obese patients

Cholecystokinin (CCK) and gastrin (G) and their receptors (CCK1 and CCK2) are involved in multiple physiological functions. Notably, CCK1R plays a role in the regulation of food intake whereas both CCK1R and CCK2R play a role in the regulation of pancreatic endocrine function. CCK1R and CCK2R may therefore serve as pharmacological targets in diabetes and obesity and genes encoding these receptors may be candidate genes in the pathogenesis of the diseases. In this study, we used single nucleotide polymorphism analysis and allele specific amplification for mutation screening of the CCK2 receptor gene and family linkage study. Mutated receptors were constructed, expressed in COS-7 cells for analysis of their binding and functional properties. V125I-CCK2 receptor variant was found in 2 out of 18 type 2 diabetes mellitus families tested. V125I mutation co-segregated in those 2 initial families, but further association studies showed that this mutation was not associated with diabetes or early age at diagnosis of the disease. V125I-CCK2 receptor high affinity sites exhibited a 2-fold enhanced binding affinity for CCK which was correlated to a slightly increased potency in coupling to inositol phosphate production. Since CCK2 receptor is expressed in pancreatic glucagon-producing cells in humans and is involved in secretion of glucagon, an increase of binding affinity of the mutated CCK2 receptor could enhance glucagon secretion in patients bearing V125I mutation. We also characterized a mutant of the CCK1 receptor which was previously identified in an obese patient. This mutant, V365I-CCK1, demonstrated a decreased level of expression (26%) and efficacy (25%) to stimulate inositol phosphates. It can therefore be expected that in humans bearing V365I mutation, decreases in CCK1 receptor expression and coupling efficiency may affect CCK-induced regulation of satiety. Polymorphism or mutations in the CCK receptors may be involved in type 2 diabetes mellitus and obesity. However, further studies are necessary to precisely evaluate this role in humans.

Cholecystokinin mediates depression of feed intake in dairy cattle fed high fat diets

Two experiments were conducted to investigate the effects of 1) different concentrations of dietary fat and 2) i.v. administration of a cholecystokinin receptor antagonist (MK-329) on feed intake and plasma concentrations of hormones and metabolites in dairy cattle. In Experiment 1, 4 lactating Holstein cows were used in a 4 x 4 Latin square design. Treatments were diets with 1) no fat added, 2) 30 g fat/kg feed (calcium salts of long-chain fatty acids as fat supplement), 3) 60 g fat/kg, and 4) 90 g fat/kg added. Cows were fed once daily a diet of concentrate, corn silage, alfalfa haylage, and alfalfa pellets. Dry matter intake decreased linearly with increasing concentrations of dietary fat (P < 0.0001). Overall plasma concentrations of nonesterified fatty acids (P < 0.0001), triacylglycerol (P < 0.0006), and cholecystokinin (P < 0.02), increased linearly with each level of dietary fat, but there was a linear decrease in plasma insulin (P < 0.0008). In Experiment 2, 4 nonpregnant and nonlactating Holstein heifers were used in a cross-over design in a 2 x 2 factorial arrangement of treatments. Treatments were diet (fatty acids, 27 g/kg vs 103 g/kg diet dry matter) and i.v. injections (MK-329 vs vehicle). Heifers were fed once daily a total mixed ration of corn silage, cracked corn and soybean meal with or without fat supplement. Diets were switched by period and either MK-329 (70 microg/kg body weight) or its vehicle was injected i.v. at 2 hr postfeeding. Daily dry matter intake was decreased by feeding the high fat diet (P < 0.02) but was not affected by injections. Injection of MK-329, however, increased dry matter intake by 92% in heifers fed the high fat diet during the first 2 hr postinjection compared to vehicle injection. Plasma pancreatic polypeptide concentration was increased by the high fat diet at 2 hr postfeeding (P < 0.02) but was lowered by MK-329 at 1 hr postinjection (P < 0.001). Plasma insulin was lowered by the high fat diet (P < 0.01) but was not affected by injections. The elevated plasma cholecystokinin concentration may have mediated depressed feed intake of dairy cattle fed the high fat diets.

Antidiabetogenic action of cholecystokinin-8 in type 2 diabetes

Cholecystokinin (CCK) is a gut hormone and a neuropeptide that has the capacity to stimulate insulin secretion. As insulin secretion is impaired in type 2 diabetes, we explored whether exogenous administration of this peptide exerts antidiabetogenic action. The C-terminal octapeptide of CCK (CCK-8) was therefore infused i.v. (24 pmol/kg x h) for 90 min in six healthy postmenopausal women and in six postmenopausal women with type 2 diabetes. At 15 min after start of infusion, a meal was served and ingested during 10 min. On a separate day, saline was infused instead of CCK-8. In both healthy subjects and subjects with type 2 diabetes, CCK-8 reduced the increase in circulating glucose after meal ingestion and potentiated the increase in circulating insulin. The ratio between the area under the curves for serum insulin and plasma glucose during the 15- to 75-min period after meal ingestion was increased by CCK-8 by 198 +/- 18% in healthy subjects (P = 0.002) and by 474 +/- 151% (P = 0.038) in subjects with type 2 diabetes. In contrast, the increase in the circulating levels of gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), or glucagon after meal ingestion was not significantly affected by CCK-8. The study therefore shows that CCK-8 exerts an antidiabetogenic action in both healthy subjects and type 2 diabetes through an insulinotropic action that most likely is exerted trough a direct islet effect. As at the same time, CCK-8 was infused without any adverse effects, the study suggests that CCK is a potential treatment for type 2 diabetes.

Duodenal loading with glucose induces fos expression in rat brain: selective blockade by devazepide

The role of CCK in mediating neuronal activity in the brain in response to dietary carbohydrate was measured by detecting Fos immunoreactivity in response to duodenal glucose load in rats after administration of the CCK-A receptor antagonist devazepide. In adult, male Sprague-Dawley rats, infusion for 30 min of 545 mg (2.18 kcal) dextrose through a duodenal cannula induced Fos expression in the nucleus of the solitary tract (NTS), area postrema (AP), lateral division of the central nucleus of the amygdala (CeAL), and the external subnucleus of the lateral parabrachial nucleus (LPBE). Devazepide treatment (1 mg/kg) attenuated Fos expression in the NTS and AP by 81 and 78%, respectively, but not in the CeAL or LPBE. These results indicate that central neuronal activation is elicited by dietary glucose in the intestinal lumen and that activation of neurons in the NTS and AP is mediated by CCK-A receptors.

Cholestyramine influences meal-stimulated pancreaticobiliary function and plasma cholecystokinin independent of gastric emptying and food digestion

BACKGROUND

Cholestyramine enhances gallbladder emptying and plasma cholecystokinin responses to oral ingestion of a mixed meal. It is not known whether this effect occurs independently of alterations in gastric emptying or maldigestion of nutrients.

METHODS

We perfused 15 g of an amino acid meal intraduodenally for 60 min in seven healthy volunteers, once with and once without cholestyramine. Intraduodenal perfusion of saline with or without cholestyramine (6 g/h) was started 60 min before the amino acid meal and continued for 2 h.

RESULTS

Cholestyramine markedly enhanced the incremental plasma cholecystokinin response to the meal from 36 +/- 12 to 139 +/- 25 pmol/l x 60 min (P < 0.005), incremental amylase output from 2.4 +/- 0.7 to 5.7 +/- 0.7 kU/h (P < 0.05), and incremental integrated gallbladder contraction from 1948 +/- 235 to 2840 +/- 189% x 60 min (P < 0.05).

CONCLUSION

The enhancing effect of cholestyramine on postprandial gallbladder contraction, pancreatic enzyme secretion, and plasma cholecystokinin release is not dependent on gastric emptying rates or appropriate digestion of nutrients.

Oral glucose ingestion stimulates cholecystokinin release in normal subjects and patients with non-insulin-dependent diabetes mellitus

The role of glucose in the regulation of plasma cholecystokinin (CCK) level was investigated in healthy control subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). Plasma CCK concentration was determined by a specific and sensitive bioassay and by a highly sensitive and reliable double-antibody radioimmunoassay using OAL-656 as an antiserum. In control subjects, ingestion of Trelan G-75 (1,200 mOsm/L,225 mL), which is equivalent to 75 g glucose as metabolic products, caused a rapid and significant increase in plasma CCK bioactivity from 1.3 +/- 0.2 to a peak of 5.8 +/- 0.6 pmol/L and immunoreactive CCK concentration from 1.2 +/- 0.1 to 4.6 +/- 0.6 pmol/L. Ingestion of 75 g glucose in 225 mL water (33.3% solution) increased plasma CCK bioactivity to a similar degree to that observed following Trelan G-75 (peak response, 4.5 +/- 0.4 pmol/L). The same volume of 0.9% NaCl solution or water failed to increase plasma CCK concentration. A smaller dose of glucose (50 b/150 mL water) increased plasma CCK concentration, although the peak level (3.0 +/- 0.5 pmol/L) was less than that observed following 75 g glucose. In patients with NIDDM, Trelan G-75 ingestion increased CCK concentration, but the peak level was lower, albeit insignificantly, than that of normal subjects. When the maximal increment of plasma CCK above the basal value was compared between control and NIDDM subjects, the differences were statistically significant (NIDDM, 3.6 +/- 0.1 pmol/L; control, 5.0 +/- 0.4; P < .01). However, integrated CCK responses to Trelan G-75 in NIDDM (165.8 +/- 15.5 pmol/120 min) were not significantly different from those in control subjects (189.8 +/- 15.9 pmol/120 min). Peak CCK bioactivity occurred within 10 to 30 minutes of ingestion, preceding the increase in glucose and insulin. These results suggest a possible effect of CCK on insulin release in humans, and that the CCK secretory response to glucose in well-controlled diabetic patients is not significantly altered.

CCK-58: a novel reagent for studying the regulation of cholecystokinin bioactivity

CCK-58 has been shown to be the major circulating form of the hormone in the dog and human. To date, there have been no reports on its biological activity in vivo. We report here that CCK-8 and CCK-58 were equipotent in decreasing gastric motor function after bolus doses and in stimulating protein secretion after continuous infusion in urethane-anesthetized rats. The present results are the first on the in vivo activity of CCK-58, and indicate that because CCK-58 is equipotent to CCK-8, and because it is a major released and circulating form, it may be considered as a major contributor to the expression of cholecystokinin bioactivity.

Physiological augmentation of amino acid-induced insulin secretion by GIP and GLP-I but not by CCK-8

It was the aim of this study to test insulinotropic actions of cholecystokinin octapeptide (CCK-8), gastric inhibitory polypeptide (GIP), and glucagon-like peptide I (GLP-I)-(7--36) amide at basal glucose but physiologically elevated amino acid concentrations. Therefore, in nine fasting healthy volunteers, an amino acid mixture was infused intravenously (12.6 g/h over 120 min). On separate occasions, from 30 to 120 min, placebo (0.9% NaCl-1% human serum albumin), synthetic sulfated CCK-8 (0.5 pmol.kg-1.min-1), human GIP (1 pmol.kg-1.min-1), or GLP-I-(7--36) amide (0.3 pmol.kg-1.min-1) was infused intravenously to mimic physiological increments after a meal. The amino acid infusion lead to a small increment in plasma glucose from 4.8 +/- 0.2 to 5.0 +/- 0.2 mmol/l and significantly elevated insulin and C-peptide concentrations. GIP and GLP-I-(7--36) amide further stimulated insulin (1.8-fold, P = 0.0001 and 0.004, respectively) and C-peptide (1.3-fold, P = 0.0003 and 0.013, respectively), with a subsequent slight reduction in plasma glucose (P < 0.0001). Insulin and C-peptide then decreased again in parallel. CCK-8 was without effect on insulin and C-peptide levels. In conclusion, GIP and GLP-I-(7--36) amide are not only able to interact with elevated plasma glucose but are insulinotropic also with physiologically raised amino acid concentrations. Such an interaction could play a role after the ingestion of mixed meals. Cholecystokinin, on the other hand, is not a physiological incretin also under these conditions.

Effect of endogenous cholecystokinin on postprandial gallbladder refilling. Ultrasonographic study in healthy subjects and in gallstone patients

The postprandial release of cholecystokinin (CCK) regulates gallbladder (GB) contraction but little is known about the role, if any, of the still-elevated CCK blood levels on subsequent GB refilling. To assess the role of CCK in GB refilling, a CCK-receptor antagonist, loxiglumide, or saline were infused intravenously in a random double-blind fashion after the ingestion of a liquid test meal in 16 healthy subjects. An identical study protocol was performed in 10 GB "contractor" patient with radiolucent stones to ascertain whether the reported reduced CCK effect on GB emptying also affects GB refilling. GB volumes were assessed ultrasonographically in the fasting state and for 150 min at 15-min intervals after meal ingestion. GB volumes during postprandial refilling were significantly greater during loxiglumide than placebo infusion (P < 0.01), but they did not differ between gallstone and control subjects. In conclusion, postprandial endogenous CCK has a relevant role in delaying GB refilling, and this effect is not altered in patients with radiolucent gallstones.

Effect of bile salt binding or protease inactivation on plasma cholecystokinin and gallbladder responses to bombesin

BACKGROUND/AIMS

Bombesin-stimulated plasma cholecystokinin levels decrease after an initial increase despite continuous infusion of bombesin. The aim of this study was to determine if a feedback mechanism, mediated by bile salts or proteolytic enzymes, is responsible for this decline.

METHODS

Bombesin (1.0 ng.kg-1.min-1) was infused into volunteers for 180 minutes on separate occasions. Cholestyramine, colestipol, camostate, or saline were perfused intraduodenally during the second hour of the tests. Cholestyramine was also administered without infusion of bombesin.

RESULTS

Colestipol and cholestyramine, dependent on their bile salt-binding capacity, markedly enhanced (P < 0.05) bombesin-stimulated plasma cholecystokinin from 2.1 +/- 0.5 pmol/L to 6.4 +/- 2.2 pmol/L and 12.1 +/- 3.3 pmol/L (P < 0.05 vs. colestipol), respectively, and further decreased gallbladder volume (P < 0.05) from 9.4 +/- 1.6 mL to 2.0 +/- 0.4 mL and 2.2 +/- 0.5 mL, respectively. The protease inhibitor camostate had no effect. Bile salt precipitation also enhanced plasma pancreatic polypeptide responses (P < 0.01) but did not alter gastrin responses. Plasma cholecystokinin responses to cholestyramine without bombesin infusion varied considerably, but increments were highly correlated to decreases in gallbladder volume (r = 0.91; P < 0.005).

CONCLUSIONS

Bile salt sequestration but not protease inactivation enhances plasma cholecystokinin and gallbladder responses to bombesin infusion in humans.

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.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Pancreatic polypeptide infusions reduce food intake in Prader-Willi syndrome

Prader-Willi syndrome is characterized by dramatic hyperphagia and morbid obesity, and is associated with a deficiency in basal and meal-stimulated serum pancreatic polypeptide (PP) levels. Intravenous infusions of pancreatic polypeptide (90 min, 50 pmol/kg/h) restored normal serum PP levels, and a regimen of morning and afternoon PP infusions was found to significantly reduce food intake in Prader-Willi subjects. Food intake was evaluated in a 60-min free-feeding test that shows high reliability and validity. Basal food intake during saline infusions was striking (approximately 60 chicken sandwich quarters), and this intake was reduced overall by approximately 12% during PP infusions. This reduction was apparent only for female subjects, and may have reflected enhanced satiation rather than an overall suppression of food intake. No differences were apparent across subjects, in either basal food intake or the PP-related decrease in food intake, in the presence or absence of the widely recognized chromosomal marker for this syndrome [deletion of 15(q11-q13)]. More specific gene defects as recently reported in these subjects, however, suggest that the Prader-Willi syndrome may represent an important model for the study of food intake regulation.

Importance of cholecystokinin in peptide-YY release in response to pancreatic juice diversion

It is generally accepted that peptide-YY (PYY), an ileocolonic peptide, is released by luminal nutrients and exogenous cholecystokinin (CCK). The importance of luminal nutrients as major PYY releasers was recently challenged when significant increases in plasma PYY were observed in response to pancreatic juice diversion in rats free of luminal nutrients. These recent data raise questions concerning the potential mediators of PYY release. This study was undertaken therefore to determine the role of endogenous CCK and the effects of exogenous caerulein, secretin and bombesin on PYY release. Male Wistar rats prepared with pancreatic, biliary, duodenal and jugular vein cannulae were used 4-7 days postoperatively. Pancreatic juice diversion significantly increased pancreatic volume and protein output with concomitant increases in plasma CCK and PYY concentrations. During pancreatic juice diversion, infusion of MK-329, a CCK-receptor antagonist, did not affect CCK release but completely abolished pancreatic volume and protein output and PYY release. The intraduodenal infusion of SBTI significantly stimulated pancreatic secretion and CCK release without any effect on PYY release. Furthermore, infusions of the CCK analog, caerulein, secretin and bombesin had no effect on PYY release. These results suggest the involvement of endogenous CCK in PYY release but this mediation seems to necessitate the participation of other as yet unknown factors since exogenous caerulein, secretin or bombesin cannot induce PYY release when given alone.

Physiological role of cholecystokinin on postprandial insulin secretion and gastric meal emptying in man. Studies with the cholecystokinin receptor antagonist loxiglumide

Cholecystokinin was previously proposed to play an important role in the regulation of postprandial insulin secretion either indirectly, by inhibiting gastric meal emptying, or directly, by acting as an incretin promoting the release of insulin. The aim of this investigation was therefore to clarify the role of endogenous cholecystokinin in the regulation of insulin release and gastric emptying applying the highly potent and specific cholecystokinin receptor antagonist loxiglumide. Five healthy volunteers were examined after an overnight fast. Gastric meal emptying was measured by the double indicator technique using a multiple lumen tube in the duodenum and 99mTc-diethylenetriamine pentaacetate as a meal marker and polyethylene glycol 4000 as a duodenal perfusion marker. Postprandial insulin, C-peptide, cholecystokinin and glucose levels were measured after ingestion of two isocaloric meals of a) Ensure (containing fat, protein and glucose), and b) a pure glucose meal (1.11 mol/l). The meals were given either with an intravenous infusion of loxiglumide (22 mumol.kg-1.h-1) or placebo. The infusion of loxiglumide markedly accelerated the gastric emptying of the mixed meal (area under curve, 5576 +/- 352 min vs 3498 +/- 109 min; p less than 0.001) and the pure glucose meal (area under curve 5662 +/- 537 min vs 3551 +/- 534 min; p less than 0.05). Simultaneously, loxiglumide induced a more rapid rise in postprandial insulin levels after both meals resulting in significantly higher (p less than 0.05) insulin levels during the first postprandial hour, but similar insulin levels in the second postprandial hour. Accordingly, we found a close correlation between meal emptying and insulin release (r = 0.748, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholecystokinin-receptor blockade on pancreatic and biliary function in healthy volunteers

This study used the specific cholecystokinin (CCK)-receptor antagonist loxiglumide to evaluate whether endogenous CCK, which is released after a meal, regulates pancreatic and biliary functions. Eight healthy volunteers were studied twice on separate days. The subjects received a continuous intraduodenal infusion of a 750-kcal liquid test meal for 2 hours either with or without IV infusion of 5 mg.kg-1.h-1 of loxiglumide. Loxiglumide at this dose abolishes the actions of CCK at various target organs including gallbladder and pancreas, when given at doses that mimic postprandial plasma concentrations of CCK. Loxiglumide markedly decreased the meal-stimulated outputs of amylase, trypsin, and chymotrypsin by 55%-70% of control values but only slightly decreased duodenal volume (25% inhibition of mean integrated secretion). Loxiglumide abolished gallbladder emptying induced by infusion of nutrients and even increased gallbladder volumes when compared with prior fasting values. Correspondingly, loxiglumide almost abolished the output of bilirubin after infusion of nutrients. However, loxiglumide failed to alter the increase in circulating concentrations of glucose, insulin, and C peptide after infusion of nutrients. The present results show that CCK is one of several factors that regulate pancreatic protein secretion after absorption of nutrients. However, CCK is probably not involved in regulation of pancreatic secretion of fluid. In contrast, gallbladder function is mainly regulated by CCK, both in terms of its emptying after intestinal absorption of nutrients and in terms of maintenance of its fasting volume. Cholecystokinin does not play a major physiological role as an insulinotropic factor.

Priming effect of glucagon-like peptide-1 (7-36) amide, glucose-dependent insulinotropic polypeptide and cholecystokinin-8 at the isolated perfused rat pancreas

The priming effect of glucagon-like peptide-1 (7-36) amide (GLP-1 (7-36) amide), glucose-dependent insulin-releasing polypeptide (GIP) and cholecystokinin-8 (CCK-8) on glucose-induced insulin secretion from rat pancreas was investigated. The isolated pancreas was perfused in vitro with Krebs-Ringer bicarbonate buffer containing 2.8 mmol/l glucose. After 10 min this medium was supplemented with GLP-1 (7-36) amide, GIP or CCK-8 (10, 100, 1000 pmol/l) for 10 min. After an additional 10 min period with 2.8 mmol/l glucose alone, insulin secretion was stimulated with buffer containing 10 mmol/l glucose for 44 min. In control experiments the typical biphasic insulin response to 10 mmol/l glucose occurred. Pretreatment of the pancreas with GIP augmented insulin secretion: 10 pmol/l GIP enhanced only the first phase of the secretory response to 10 mmol/l glucose; 100 and 1000 pmol/l GIP stimulated both phases of hormone secretion. After exposure to CCK-8, enhanced insulin release during the first (at 10 and 1000 pmol/l CCK-8) and the second phase (at 1000 pmol/l) was observed. Priming with 100 pmol/l GLP-1 (7-36) amide significantly amplified the first and 1000 pmol/l GLP-1 (7-36) amide both secretion periods, 10 pmol/l GLP-1 (7-36) amide had no significant effect. All three peptide hormones influenced the first, quickly arising secretory response more than the second phase. Priming with forskolin (30 mM) enhanced the secretory response to 10 mM glucose plus 0.5 nM GLP-1 (7-36) amide 4-fold. With a glucose-responsive B-cell line (HIT cells), we investigated the hypothesis that the priming effect of GLP-1 (7-36) amide is mediated by the adenylate cyclase system. Priming with either IBMX (0.1 mM) or forskolin (2.5 microM) enhanced the insulin release after a consecutive glucose stimulation (5 mM). This effect was pronounced when GLP-1 (7-36) amide (100 pM) was added during glucose stimulation. Priming capacities of intestinal peptide hormones may be involved in the regulation of postprandial insulin release. The incretin action of these hormones can probably, at least in part, be explained by these effects. The priming effect of GLP-1 (7-36) amide is most likely mediated by the adenylate cyclase system.