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

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.

Effects of various food ingredients on gall bladder emptying

Background/objectives:

The emptying of the gall bladder in response to feeding is pivotal for the digestion of fat, but the role of various food ingredients in contracting the gall bladder postprandially is not well understood. We hypothesized that different food ingredients, when consumed, will have a different effect on stimulating gall bladder emptying. To investigate this we designed two randomized, investigator-blind, cross-over studies in healthy subjects using magnetic resonance imaging (MRI) to measure gall bladder volumes serially and non-invasively.

Subjects/methods:

Study 1: exploratory study evaluating the effects of 10 different food ingredients on gall bladder emptying in eight healthy subjects. The choice of ingredients varied from common items like coffee, tea and milk to actives like curcumin and potato protease inhibitor. Study 2: mechanistic study investigating the cholecystokinin (CCK) dose response to the best performer ingredient from Study 1 in 21 healthy subjects four ways.

Results:

The largest gall bladder volume change in Study 1 was observed with fat, which therefore became the dose-response ingredient in Study 2, where the maximum % gall bladder volume change correlated well with CCK.

Conclusions:

These serial test-retest studies showed that the fasted gall bladder volume varied remarkably between individuals and that individual day-to-day variability had wide coefficients of variation. Improved knowledge of how to stimulate bile release using food ingredients will be useful to improve in vitro–in vivo correlation of bioavailability testing of hydrophobic drugs. It could improve performance of cholesterol-lowering plant stanol and sterol products and possibly aid understanding of some cholesterol gallstone disease.

The effects of intraduodenal nutrient infusion on serum CCK, LES pressure, and gastroesophageal reflux

BACKGROUND

Fats cause reflux symptoms in many patients and cholecystokinin (CCK) may play a role. This study was designed to evaluate the effects of intraduodenal nutrient infusion on serum CCK levels, lower esophageal sphincter (LES) pressure, and gastroesophageal reflux (GER).

METHODS

Twenty-four asymptomatic volunteers were studied. A Dent sleeve catheter assessed LES function while an impedance-pH catheter measured reflux events. Participants were randomized to fat (F), carbohydrate (C) or protein (P) infusion. Serum CCK and LES pressures were measured at baseline and after nutrient infusion.

KEY RESULTS

Baseline LES pressures and CCK levels were similar in all three groups. A significant linear decrease was found in LES pressure during F, but not C or P, infusion (P=0.004). A significant interaction effect was noted between the infusion groups and CCK levels (P=0.002). A significant linear increase was noted in CCK levels during F but not during C or P infusion (P=0.02). A significant inverse correlation was found between CCK levels and LES pressure (ρ=-0.43; P=0.04). Esophageal acid exposure was significantly increased in the F infusion group (median; interquartile range: 1.10%; 0.25-4.7%) compared to both the C (0.03%; 0.00-0.39%) and P infusion (0.03%; 0.00-0.39%) groups (P=0.04).

CONCLUSIONS & INFERENCES

Intraduodenal F infusion was associated with an increase in CCK levels, while P and C were not. LES pressure decreased significantly after fat infusion and reflux events were more frequent. Fat-induced CCK release is another mechanism that contributes to GER.

Gastric emptying of hexose sugars: role of osmolality, molecular structure and the CCK₁ receptor

BACKGROUND

It is widely reported that hexose sugars slow gastric emptying (GE) via osmoreceptor stimulation but this remains uncertain. We evaluated the effects of a panel of hexoses of differing molecular structure, assessing the effects of osmolality, intra-individual reproducibility and the role of the CCK(1) receptor, in the regulation of GE by hexoses.

METHODS

Thirty one healthy non-obese male and female subjects were studied in a series of protocols, using a (13) C-acetate breath test to evaluate GE of varying concentrations of glucose, galactose, fructose and tagatose, with water, NaCl and lactulose as controls. GE was further evaluated following the administration of a CCK(1) receptor antagonist. Three subjects underwent repeated studies to evaluate intra-individual reproducibility.

KEY RESULTS

At 250 mOsmol, a hexose-specific effect was apparent: tagatose slowed GE more potently than water, glucose and fructose (P < 0.05). Fructose (P < 0.05) also slowed GE, but with substantial inter-, but not intra-, individual differences. As osmolality increased further the hexose-specific differences were lost. At 500 mOsmol, all hexoses slowed GE compared with water (P < 0.05), whereas lactulose and saline did not. The slowing of GE by hexose sugars appeared to be CCK(1) receptor-dependent.

CONCLUSIONS & INFERENCES

The effects of hexose sugars on GE appear related to their molecular structure rather than osmolality per se, and are, at least in part, CCK(1) receptor-dependent.

Effects of the phases of the menstrual cycle on gastric emptying, glycemia, plasma GLP-1 and insulin, and energy intake in healthy lean women

There is evidence that the menstrual cycle affects appetite, such that energy intake is lower during the follicular compared with the luteal phase. Gastric emptying influences energy intake, glycemia, and plasma glucagon-like peptide-1 (GLP-1), insulin, and cholecystokinin (CCK) release. We hypothesized that 1) gastric emptying of a glucose drink is slower, and glycemia, plasma hormones, hunger, and energy intake are less, during the follicular compared with the luteal phase; 2) the reduction in the latter parameters during the follicular phase are related to slower gastric emptying; and 3) these parameters are reproducible when assessed twice within a particular phase of the menstrual cycle. Nine healthy, lean women were studied on three separate occasions: twice during the follicular phase (days 6-12) and once during the luteal phase (days 18-24). Following consumption of a 300-ml glucose drink (0.17 g/ml), gastric emptying, blood glucose, plasma hormone concentrations, and hunger were measured for 90 min, after which energy intake at a buffet meal was quantified. During the follicular phase, gastric emptying was slower (P < 0.05), and blood glucose (P < 0.01), plasma GLP-1 and insulin (P < 0.05), hunger (P < 0.01), and energy intake (P < 0.05) were lower compared with the luteal phase, with no differences for CCK or between the two follicular phase visits. There were inverse relationships between energy intake, blood glucose, and plasma GLP-1 and insulin concentrations with the amount of glucose drink remaining in the stomach at t = 90 min (r < -0.6, P < 0.05). In conclusion, in healthy women 1) gastric emptying of glucose is slower, and glycemia, plasma GLP-1 and insulin, hunger, and energy intake are less during the follicular compared with the luteal phase; 2) energy intake, glycemia, and plasma GLP-1 and insulin are related to gastric emptying; and 3) these parameters are reproducible when assessed twice during the follicular phase.

Effect of age and frailty on ghrelin and cholecystokinin responses to a meal test

BACKGROUND

Ghrelin and cholecystokinin (CCK) are among the peripheral signals that regulate hunger and satiety.

OBJECTIVE

The objective was to assess whether ghrelin and CCK responses to a standard nutritional load are related to age and frailty.

DESIGN

Ghrelin, CCK, insulin, glucose, and 4-h visual analog hunger scale curves after a standard nutritional load test (380 kcal) were described and compared between 3 groups: old (>75 y) and frail persons (group A), old (>75 y) but nonfrail persons (group B), and young (25-65 y) adults (group C).

RESULTS

Frail persons showed no postprandial ghrelin suppression, and old subjects, frail and nonfrail, showed no significant postprandial ghrelin recovery compared with young adults. Frailty was also associated with lower fasting ghrelin concentrations. No differences in fasting CCK were observed between young and old persons; however, postprandial CCK concentrations were enhanced in young persons, whereas no frailty effect on the CCK curve was observed in the old subjects. No correlations between mean ghrelin and hunger values over time were found, but strong negative correlations were shown between CCK and hunger (group A: r(s) = -0.88, P = 0.009; group B: r(s) = -0.86, P = 0.014; group C: r(s) = -0.71, P = 0.071) and insulin and hunger (group A: r(s) = -0.901, P = 0.006; group B: r(s) = -0.964, P < 0.001; group C: r(s) = -0.929, P = 0.003).

CONCLUSIONS

Advanced age determines a poorer ghrelin postprandial recuperation phase, a reduced CCK postprandial response, and an exaggerated postprandial insulin release. A loss of ghrelin prandial rhythm is present in old frail persons. The impaired response of these hunger regulatory hormones with age might contribute to the mechanisms of anorexia associated with aging.

Feed intolerance in critical illness is associated with increased basal and nutrient-stimulated plasma cholecystokinin concentrations

OBJECTIVE

Delayed gastric emptying and intolerance to gastric feeding occur frequently in the critically ill. In these patients, gastric motor responses to nutrients are disturbed. Cholecystokinin (CCK) slows gastric emptying. The aim of this study was to determine plasma CCK concentrations during fasting and in response to small-intestine nutrient infusion in critically ill patients.

DESIGN

Randomized, controlled trial.

SETTING

Level 3, mixed medical and surgical intensive care unit.

SUBJECTS

A total of 31 mechanically ventilated, critically ill patients (23 men, 51 +/- 3 yrs) and 28 healthy subjects (21 men, 43 +/- 2 yrs).

INTERVENTIONS

Subjects received two 60-min duodenal infusions of Ensure (complete balanced nutrition), at 1 and 2 kcal/min, in a randomized, single-blind fashion. The nutrient infusions were separated by a 2-hr "washout" period. Blood samples for measurement of plasma CCK concentrations were obtained immediately before and every 20 mins during nutrient infusion.

MEASUREMENTS AND MAIN RESULTS

Baseline and nutrient-stimulated plasma CCK concentrations were higher in critically ill patients compared with healthy subjects (p < .001). The magnitude of the rise in plasma CCK in response to nutrients was also greater in the critically ill (p < .01). Of the 23 patients who received enteral nutrition before the study, nine were intolerant of gastric feeding. In these patients, both the baseline plasma CCK concentration and the magnitude of CCK increase during nutrient infusions were greater than in patients with feed tolerance (p < .002). Impaired renal function was associated with an increased baseline CCK concentration but had no effect on the CCK response to nutrients.

CONCLUSIONS

Both fasting and nutrient-stimulated plasma CCK concentrations are increased in critically ill patients, particularly in those with feed intolerance. This may provide a humoral mechanism for delayed gastric emptying seen in critical illness.

CCK1 antagonists: are they ready for clinical use?

Cholecystokinin (CCK) is a peptide hormone which is found both in the gastrointestinal tract throughout the human small intestine and nerves in the myenteric plexus of the enteric nervous system and in the central nervous system. This dual location constitutes the anatomical basis for this in functions as a hormone and a neurotransmitter implicated in the regulation of both systems. CCK regulates not only motor functions in the gastrointestinal tract like lower oesophageal sphincter relaxation, gastric secretion and emptying, gall bladder contractility and bile secretion into the duodenum, intestinal and colonic motility, but also sensory functions and plays a role in the regulation of food intake. These effects are mediated through selective receptors CCK1 and CCK2. Over the last few years, research has focused on understanding the role of CCK, its receptors with antagonists at the biological, pharmacological, clinical and therapeutic level. As far as the CCK1 antagonists is concerned, important inroads have been made in the potential role of these antagonists in the treatment of GERD, IBS and pancreatitis. They have also shown encouraging results in sphincter of Oddi dysfunction and some gastrointestinal cancers. This review focuses on the recent ad vances of the biological role of CCK and their CCK1 antagonists: their current basic and clinical status in gastroenterology, with particular emphasis on the potential therapeutic role of the CCK1 antagonists and future research directions.

Gallbladder contraction, gastric emptying and antral motility: Single visit assessment of upper GI function in untreated celiac disease using echo-planar MRI

PURPOSE

To assess gallbladder contraction, gastric emptying, and antral motility in untreated celiac patients and healthy controls using a single MRI examination.

MATERIALS AND METHODS

Gallbladder emptying, gastric emptying, and antral motility were measured in 15 celiac patients and 15 age/sex-matched healthy controls following a 323-kcal test meal using EPI techniques. Postprandial dyspepsia scores were recorded on a questionnaire.

RESULTS

Fasting gallbladder volume (P=0.01) and the volume of bile ejected postprandially (P=0.014) were increased in celiacs. Gastric emptying tended to be slower in celiacs (P=0.142). Three celiac patients with severe postprandial dyspepsia and total villous atrophy had pathologically delayed gastric emptying and increased fasting gallbladder volume. Antral contractions were absent in five out of 14 patients (36%) five minutes after the meal, but in none of 10 volunteers in whom the antrum could be visualized (P=0.128).

CONCLUSION

This study shows that using MRI, multiple parameters related to upper gastrointestinal function in celiac disease can be measured in a single noninvasive study, whereas previously three separate visits would have been required. Celiacs have increased fasting gallbladder volumes and tend to have slower gastric emptying.

Effects of psychological stress on small intestinal motility and expression of cholecystokinin and vasoactive intestinal polypeptide in plasma and small intestine in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and expression of cholecystokinin (CCK) and vasoactive intestinal polypeptide (VIP) in plasma and small intestine, and to explore the relationship between small intestinal motor disorders and gastrointestinal hormones under psychological stress.

METHODS: Thirty-six mice were randomly divided into psychological stress group and control group. A mouse model with psychological stress was established by housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. CCK and VIP levels in plasma and small intestine in mice were measured by radioimmunoassay (RIA).

RESULTS: Small intestinal transit was inhibited (52.18±19.15% vs 70.19±17.79%, P<0.01) in mice after psychological stress, compared to the controls. Small intestinal CCK levels in psychological stress mice were significantly lower than those in the control group (0.75±0.53 μg/g vs 1.98±1.17 μg/g, P<0.01), whereas plasma CCK concentrations were not different between the groups. VIP levels in small intestine were significantly higher in psychological stress mice than those in the control group (8.45±1.09 μg/g vs 7.03±2.36 μg/g, P<0.01), while there was no significant difference in plasma VIP levels between the two groups.

CONCLUSION: Psychological stress inhibits the small intestinal transit, probably by down-regulating CCK and up-regulating VIP expression in small intestine.

Monitoring of gallbladder and gastric coordination by EPI

PURPOSE

To assess for the first time the potential of echo-planar magnetic resonance imaging (EPI) for measuring simultaneously both gallbladder and gastric emptying.

MATERIALS AND METHODS

Eight healthy subjects ingested 500 mL of an acid-stable liquid test meal containing 15% olive oil and flavoring. Every 20 minutes for three hours thereafter, a rapid EPI multislice set was acquired across the whole abdomen, using a dedicated whole-body 0.5-T EPI scanner.

RESULTS

The bile in the gallbladder and the test meal in the stomach appeared bright in the EPI images, aiding localization and region of interest analysis. We measured the gallbladder emptying curve and fitted the data to a simple analytical model. The mean fasted gallbladder volume was 25 +/- 4 mL, comparable to previously published MRI and ultrasound values. Gastric emptying data fitted well to a linear model linear (R2 = 0.99), and we observed an exponential (R2 = 0.98) relationship between gallbladder and gastric volumes for the first 90 minutes.

CONCLUSION

This study shows the potential of EPI to monitor simultaneously and noninvasively the emptying of the gallbladder and of the gastric lumen. No contrast enhancing agents are needed. This method could overcome the limitations of previous gamma scintigraphy and ultrasound techniques.