Further characterisation of the 'ileal brake' reflex in man--effect of ileal infusion of partial digests of fat, protein, and starch on jejunal motility and release of neurotensin, enteroglucagon, and peptide YY

50years of oral lipid-based formulations: Provenance, progress and future perspectives

Lipid based formulations (LBF) provide well proven opportunities to enhance the oral absorption of drugs and drug candidates that sit close to, or beyond, the boundaries of Lipinski's 'rule-of-five' chemical space. Advantages in permeability, efflux and presystemic metabolism are evident; however, the primary benefit is in increases in dissolution and apparent intestinal solubility for lipophilic, poorly water soluble drugs. This review firstly details the inherent advantages of LBF, their general properties and classification, and provides a brief retrospective assessment of the development of LBF over the past fifty years. More detailed analysis of the ability of LBF to promote intestinal solubilisation, supersaturation and absorption is then provided alongside review of the methods employed to assess formulation performance. Critical review of the ability of simple dispersion and more complex in vitro digestion methods to predict formulation performance subsequently reveals marked differences in the correlative ability of in vitro tests, depending on the properties of the drug involved. Notably, for highly permeable low melting drugs e.g. fenofibrate, LBF appear to provide significant benefit in all cases, and sustained ongoing solubilisation may not be required. In other cases, and particularly for higher melting point drugs such as danazol, where re-dissolution of crystalline precipitate drug is likely to be slow, correlations with ongoing solubilisation and supersaturation are more evident. In spite of their potential benefits, one limitation to broader use of LBF is low drug solubility in the excipients employed to generate formulations. Techniques to increase drug lipophilicity and lipid solubility are therefore explored, and in particular those methods that provide for temporary enhancement including lipophilic ionic liquid and prodrug technologies. The transient nature of these lipophilicity increases enhances lipid solubility and LBF viability, but precludes enduring effects on receptor promiscuity and off target toxicity. Finally, recent efforts to generate solid LBF are briefly described as a means to circumvent the need to encapsulate in soft or hard gelatin capsules, although the latter remain popular with consumers and a proven means of LBF delivery.

Upper gastrointestinal sensitivity to meal-related signals in adult humans - relevance to appetite regulation and gut symptoms in health, obesity and functional dyspepsia

Both the stomach and small intestine play important roles in sensing the arrival of a meal, and its physico-chemical characteristics, in the gastrointestinal lumen. The presence of a meal in the stomach provides a distension stimulus, and, as the meal empties into the small intestine, nutrients interact with small intestinal receptors, initiating the release of gut hormones, associated with feedback regulation of gastrointestinal functions, including gut motility, and signaling to the central nervous system, modulating eating behaviours, including energy intake. Lipid appears to have particularly potent effects, also in close interaction with, and modulating the effects of, gastric distension, and involving the action of gut hormones, particularly cholecystokinin (CCK). These findings have not only provided important, and novel, insights into how gastrointestinal signals interact to modulate subjective appetite perceptions, including fullness, but also laid the foundation for an increasing appreciation of the role of altered gastrointestinal sensitivities, e.g. as a consequence of excess dietary intake in obesity, or underlying the induction of gastrointestinal symptoms in functional dyspepsia (a condition characterized by symptoms, including bloating, nausea and early fullness, amongst others, after meals, particularly those high in fat, in the absence of any structural or functional abnormalities in the gastrointestinal tract). This paper will review the effects of dietary nutrients, particularly lipid, on gastrointestinal function, and associated effects on appetite perceptions and energy intake, effects of interactions of gastrointestinal stimuli, as well as the role of altered gastrointestinal sensitivities (exaggerated, or reduced) in eating-related disorders, particularly obesity and functional dyspepsia.

Gastrointestinal Nutrient Infusion Site and Eating Behavior: Evidence for A Proximal to Distal Gradient within the Small Intestine?

The rapidly increasing prevalence of overweight and obesity demands new strategies focusing on prevention and treatment of this significant health care problem. In the search for new and effective therapeutic modalities for overweight subjects, the gastrointestinal (GI) tract is increasingly considered as an attractive target for medical and food-based strategies. The entry of nutrients into the small intestine activates so-called intestinal "brakes", negative feedback mechanisms that influence not only functions of more proximal parts of the GI tract but also satiety and food intake. Recent evidence suggests that all three macronutrients (protein, fat, and carbohydrates) are able to activate the intestinal brake, although to a different extent and by different mechanisms of action. This review provides a detailed overview of the current evidence for intestinal brake activation of the three macronutrients and their effects on GI function, satiety, and food intake. In addition, these effects appear to depend on region and length of infusion in the small intestine. A recommendation for a therapeutic approach is provided, based on the observed differences between intestinal brake activation.

Chronic high-fat feeding increases GIP and GLP-1 secretion without altering body weight

The incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), enhance postprandial insulin secretion, promote adipogenesis, and regulate gastrointestinal motility and food intake. To date, a consensus on how the incretin response is altered in obesity is lacking. We investigated the effects of chronic high-fat (HF) feeding on incretin secretion in the lymph fistula rat model. Male Sprague-Dawley rats (8 wk) were provided a semipurified AIN93M HF or low-fat (LF) diet ad libitum for 3 or 13 wk; a HF pair-fed (HF-PF) group was included as a control during the 3-wk feeding trial. Energy intake, body weight, and body composition were regularly monitored. At the culmination of the feeding period, an intestinal lymphatic duct cannula and duodenal infusion tube were installed. All animals were challenged with a 3-ml Ensure bolus (3.125 kcal/animal) to measure lymphatic incretin secretion. Despite a significantly higher energy intake, both the 3-wk and 13-wk HF-fed animals did not have an increase in body weight and only a slight increase in body fat compared with LF-fed rats. Following the duodenal Ensure challenge, the 3-wk and 13-wk HF-fed rats had significantly greater lymphatic GIP and GLP-1 secretion than the LF-fed animals. Additionally, the HF-PF group displayed a secretion profile similar to the HF-fed animals for GIP but a similar pattern to the LF-fed animals for GLP-1. The HF-PF data suggest that the increased GIP secretion is driven by the greater percentage of fat intake, whereas the increased GLP-1 secretion is driven by the excess caloric intake.

Pharmacology and physiology of gastrointestinal enteroendocrine cells

Gastrointestinal (GI) polypeptides are secreted from enteroendocrine cells (EECs). Recent technical advances and the identification of endogenous and synthetic ligands have enabled exploration of the pharmacology and physiology of EECs. Enteroendocrine signaling pathways stimulating hormone secretion involve multiple nutrient transporters and G protein-coupled receptors (GPCRs), which are activated simultaneously under prevailing nutrient conditions in the intestine following a meal. The majority of studies investigate hormone secretion from EECs in response to single ligands and although the mechanisms behind how individual signaling pathways generate a hormonal output have been well characterized, our understanding of how these signaling pathways converge to generate a single hormone secretory response is still in its infancy. However, a picture is beginning to emerge of how nutrients and full, partial, or allosteric GPCR ligands differentially regulate the enteroendocrine system and its interaction with the enteric and central nervous system. So far, activation of multiple pathways underlies drug discovery efforts to harness the therapeutic potential of the enteroendocrine system to mimic the phenotypic changes observed in patients who have undergone Roux-en-Y gastric surgery. Typically obese patients exhibit ∼30% weight loss and greater than 80% of obese diabetics show remission of diabetes. Targeting combinations of enteroendocrine signaling pathways that work synergistically may manifest with significant, differentiated EEC secretory efficacy. Furthermore, allosteric modulators with their increased selectivity, self-limiting activity, and structural novelty may translate into more promising enteroendocrine drugs. Together with the potential to bias enteroendocrine GPCR signaling and/or to activate multiple divergent signaling pathways highlights the considerable range of therapeutic possibilities available. Here, we review the pharmacology and physiology of the EEC system.

Advances in oral nano-delivery systems for colon targeted drug delivery in inflammatory bowel disease: selective targeting to diseased versus healthy tissue

Colon targeted drug delivery is an active area of research for local diseases affecting the colon, as it improves the efficacy of therapeutics and enables localized treatment, which reduces systemic toxicity. Targeted delivery of therapeutics to the colon is particularly advantageous for the treatment of inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn's disease. Advances in oral drug delivery design have significantly improved the bioavailability of drugs to the colon; however in order for a drug to have therapeutic efficacy during disease, considerations must be made for the altered physiology of the gastrointestinal (GI) tract that is associated with GI inflammation. Nanotechnology has been used in oral dosage formulation design as strategies to further enhance uptake into diseased tissue within the colon. This review will describe some of the physiological challenges faced by orally administered delivery systems in IBD, the important developments in orally administered nano-delivery systems for colon targeting, and the future advances of this research.

FROM THE CLINICAL EDITOR

Inflammatory Bowel Disease (IBD) poses a significant problem for a large number of patients worldwide. Current medical therapy mostly aims at suppressing the active inflammatory episodes. In this review article, the authors described and discussed the various approaches current nano-delivery systems can offer in overcoming the limitations of conventional drug formulations.

Gut chemosensing mechanisms

The enteroendocrine system is the primary sensor of ingested nutrients and is responsible for secreting an array of gut hormones, which modulate multiple physiological responses including gastrointestinal motility and secretion, glucose homeostasis, and appetite. This Review provides an up-to-date synopsis of the molecular mechanisms underlying enteroendocrine nutrient sensing and highlights our current understanding of the neuro-hormonal regulation of gut hormone secretion, including the interaction between the enteroendocrine system and the enteric nervous system. It is hoped that a deeper understanding of how these systems collectively regulate postprandial physiology will further facilitate the development of novel therapeutic strategies.

Ileal brake activation: macronutrient-specific effects on eating behavior?

BACKGROUND

Activation of the ileal brake, by infusing lipid directly into the distal part of the small intestine, alters gastrointestinal (GI) motility and inhibits food intake. The ileal brake effect on eating behavior of the other macronutrients is currently unknown.

OBJECTIVE

The objective of this study was to investigate the effects of ileal infusion of sucrose and casein on food intake, release of GI peptides, gastric emptying rate and small-bowel transit time with safflower oil as positive control.

DESIGN

This randomized, single-blind, crossover study was performed in 13 healthy subjects (6 male; mean age 26.4±2.9 years; mean body mass index 22.8±0.4 kg m(-2)) who were intubated with a naso-ileal catheter. Thirty minutes after the intake of a standardized breakfast, participants received an ileal infusion, containing control ((C) saline), safflower oil ((HL) 51.7 kcal), low-dose casein ((LP) 17.2 kcal) or high-dose casein ((HP) 51.7 kcal), low-dose sucrose ((LC) 17.2 kcal) and high-dose sucrose ((HC) 51.7 kcal), over a period of 90 min. Food intake was determined during an ad libitum meal. Visual analogue score questionnaires for hunger and satiety and blood samples were collected at regular intervals.

RESULTS

Ileal infusion of lipid, protein and carbohydrate resulted in a significant reduction in food intake compared with control (HL: 464.3±90.7 kcal, P<0.001; HP: 458.0±78.6 kcal, P<0.005; HC: 399.0±57.0 kcal, P<0.0001 vs control: 586.7±70.2 kcal, P<0.001, respectively). A reduction in energy intake was still apparent when the caloric amount of infused nutrients was added to the amount eaten during the ad libitum meal.Secretion of cholecystokinin and peptide YY but not of glucagon-like peptide-1 (7-36) was increased during ileal perfusion of fat, carbohydrates and protein. During ileal perfusion of all macronutrients, a delay in gastric emptying and intestinal transit was observed, but differences were not significant compared with control.

CONCLUSION

Apart from lipids, also sucrose and casein reduce food intake on ileal infusion, thereby activating the ileal brake. In addition to food intake, also satiety and GI peptide secretion were affected.

Ileal effect on blood glucose, HbA1c, and GLP-1 in Goto-Kakizaki rats

BACKGROUND

There have been enumerable studies on the effects of glucagon-like peptide-1 (GLP-1) on satiety and pancreatic islet function, stimulating the advocacy of surgical transposition of the ileum (rich in GLP-1-generating L-cells) higher in the gastrointestinal tract for earlier stimulation. In the Goto-Kakizaki rat with naturally occurring type 2 diabetes, we studied the influence of ileal exclusion (IE) and ileal resection (IR) on blood glucose, hemoglobin A1c (HbA1c), and GLP-1.

METHODS

In six control (Ctrl), 10 IE, and 10 IR rats, over 12 weeks of follow-up, we determined blood glucose, HbA1c, and GLP-1.

RESULTS

Two animals in the IE and IR groups did not survive to week 13. Both operated groups weighed more than the Ctrl group at baseline and at 13 weeks; thus, IE and IR did not retard weight gain (p < 0.05). All three groups were equally hyperglycemic at week 13: 255 ± 10.2 Ctrl, 262 ± 11.0 IE, 292 ± 17.8 IR (mg/dl ± SEM). The three groups had statistically identical markedly elevated HbA1c percentages at week 13: 14.7 ± 28 Ctrl, 11.7 ± 3.4 IE, 13.8 ± 3.5 IR (% ± SEM). The end-study GLP-1 values (pM ± SEM) were 5 ± 0.9 Ctrl, 33 ± 8.9 IE, and 25 ± 6.7 IR. P values for intergroup differences were IE vs. Ctrl 0.02, IR vs. Ctrl 0.02, and IE vs. IR 0.59.

CONCLUSIONS

Neither IE nor IR resulted in a decrease in the mean GLP-1 level. On the contrary, the exclusion or resection of the L-cell rich ileum raised GLP-1 levels 5- to 6-fold. This increase in the GLP-1 was not associated with the mitigation of hyperglycemia or elevated HbA1c levels.

Endocrine cells in the ileum of patients with irritable bowel syndrome

AIM

To study the ileal endocrine cell types in irritable bowel syndrome (IBS) patients.

METHODS

Ninety-eight patients with IBS (77 females and 21 males; mean age 35 years, range 18-66 years) were included, of which 35 patients had diarrhea (IBS-D), 31 patients had a mixture of both diarrhea and constipation (IBS-M), and 32 patients had constipation (IBS-C) as the predominant symptoms. The controls were 38 subjects (26 females and 12 males; mean age 40 years, range 18-65 years) who had submitted to colonoscopy for the following reasons: gastrointestinal bleeding, where the source of bleeding was identified as hemorrhoids (n = 24) or angiodysplasia (n = 3), and health worries resulting from a relative being diagnosed with colon carcinoma (n = 11). The patients were asked to complete the: Birmingham IBS symptom questionnaire. Ileal biopsy specimens from all subjects were immunostained using the avidin-biotin-complex method for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), enteroglucagon, and somatostatin cells. The cell densities were quantified by computerized image analysis, using Olympus cellSens imaging software.

RESULTS

The gender and age distributions did not differ significantly between the patients and the controls (P = 0.27 and P = 0.18, respectively). The total score of Birmingham IBS symptom questionnaire was 21 ± 0.8, and the three underlying dimensions: pain, diarrhea, and constipation were 7.2 ± 0.4, 6.6 ± 0.4, and 7.2 ± 0.4, respectively. The density of serotonin cells in the ileum was 40.6 ± 3.6 cells/mm² in the controls, and 11.5 ± 1.2, 10.7 ± 5.6, 10.0 ± 1.9, and 13.9 ± 1.4 cells/mm² in the all IBS patients (IBS-total), IBS-D, IBS-M, and IBS-C patients, respectively. The density in the controls differed significantly from those in the IBS-total, IBS-D, IBS-M, and IBS-C groups (P < 0.0001, P = 0.0001, P = 0.0001, and P < 0.0001, respectively). There was a significant inverse correlation between the serotonin cell density and the pain dimension of Birmingham IBS symptom questionnaire (r = -0.6, P = 0.0002). The density of PYY cells was 26.7 ± 1.6 cells/mm(2) in the controls, and 33.1 ± 1.4, 27.5 ± 1.4, 34.1 ± 2.5, and 41.7 ± 3.1 cells/mm² in the IBS-total, IBS-D, IBS-M, and IBS-C patients, respectively. This density differed significantly between patients with IBS-total and IBS-C and the controls (P = 0.03 and < 0.0001, respectively), but not between controls and, IBS-D, and IBS-M patients (P = 0.8, and P = 0.1, respectively). The density of PYY cells correlated significantly with the degree of constipation as recorded by the Birmingham IBS symptom questionnaire (r = 0.6, P = 0.0002). There were few PP-, enteroglucagon-, and somatostatin-immunoreactive cells in the biopsy material examined, which made it impossible to reliably quantify these cells.

CONCLUSION

The decrease of ileal serotonin cells is associated with the visceral hypersensitivity seen in all IBS subtypes. The increased density of PYY cells in IBS-C might contribute to the constipation experienced by these patients.

Effects on GLP-1, PYY, and leptin by direct stimulation of terminal ileum and cecum in humans: implications for ileal transposition

BACKGROUND

We do not have a unified, scientifically tested theory of causation for obesity and its co-morbidities, nor do we have explanations for the mechanics of the metabolic/bariatric surgery procedures. Integral to proffered hypotheses are the actions of the hormones glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and leptin. The objective of this study was to obtain blood levels of GLP-1, PYY, and leptin after stimulation of the terminal ileum and cecum by a static infusion of a food hydrolysate in morbidly obese patients undergoing a duodenal switch procedure.

SETTING

University Hospital.

METHODS

Plasma levels of GLP-1, PYY, and leptin were obtained at 0, 30, 60, 90, and 120 minutes after instillation of 240 mL of a food hydrolysate into the ileum or cecum.

RESULTS

The mean±SD GLP-1 values by cecal stimulation for 0, 30, 60, 90, and 120 minutes were: 41.3±23.2; 39.6±21.8; 38.9±19.1; 47.4±22.3; 51.7±27.3 pM, and by ileal stimulation: 55.0±32.8; 83.4±16.1; 78.7±23.8; 84.7±23.5; 76.4±25.6. The mean±SD PYY values by cecal stimulation were: 62.1±24.8; 91.1±32.8; 102.1±39.6; 119.6±37.5; 130.3±36.7, and by ileal stimulation: 73.8±41.6; 138.1±17.7; 149.5±23.3; 165.7±24.3; 155.5±29.1. Percent change in PYY levels increased ~150%, GLP-1 increased ~50%, and leptin decreased ~20%.

CONCLUSION

Direct stimulation of the human terminal ileum and cecum by a food hydrolysate elicits significant plasma GLP-1 and PYY elevations and leptin decreases, peaking at 90-120 minutes. The ileal GLP-1 and PYY responses exceed those of the cecum, and the PYY effect is about 3-fold that of GLP-1. The results of this study question the satiety premise for ileal transposition.

Liver disease secondary to intestinal failure

IFALD is a common and potentially life-threatening condition for patients with SBS requiring long-term PN. There exists the potential for decreasing its incidence by optimizing the composition and the rate of infusion of parenteral solutions, by advocating a multidisciplinary approach, and by early referral for intestinal-liver transplantation to ensure long-term survival of patients with SBS.

Lipids, CHOs, proteins: can all macronutrients put a 'brake' on eating?

The gastrointestinal (GI) tract and specifically the most distal part of the small intestine, the ileum, has become a renewed focus of interest for mechanisms targeting appetite suppression. The 'ileal brake' is stimulated when energy-containing nutrients are delivered beyond the duodenum and jejunum and into the ileum, and is named for the feedback loop which slows or 'brakes' gastric emptying and duodeno-jejunal motility. More recently it has been hypothesized that the ileal brake also promotes secretion of satiety-enhancing GI peptides and suppresses hunger, placing a 'brake' on food intake. Postprandial delivery of macronutrients to the ileum, other than unavailable carbohydrates (CHO) which bypass absorption in the small intestine en route to fermentation in the large bowel, is an uncommon event and hence this brake mechanism is rarely activated following a meal. However the ability to place a 'brake' on food intake through delivery of protected nutrients to the ileum is both intriguing and challenging. This review summarizes the current clinical and experimental evidence for activation of the ileal brake by the three food macronutrients, with emphasis on eating behavior and satiety as well as GI function. While clinical studies have shown that exposure of the ileum to lipids, CHOs and proteins may activate GI components of the ileal brake, such as decreased gut motility, gastric emptying and secretion of GI peptides, there is less evidence as yet to support a causal relationship between activation of the GI brake by these macronutrients and the suppression of food intake. The predominance of evidence for an ileal brake on eating comes from lipid studies, where direct lipid infusion into the ileum suppresses both hunger and food intake. Outcomes from oral feeding studies are less conclusive with no evidence that 'protected' lipids have been successfully delivered into the ileum in order to trigger the brake. Whether CHO or protein may induce the ileal brake and suppress food intake has to date been little investigated, although both clearly have GI mediated effects. This review provides an overview of the mechanisms and mediators of activation of the ileal brake and assesses whether it may play an important role in appetite suppression.

Hydroxypropylation of high-amylose maize starch changes digestion and fermentation-dependent parameters in rats

It was examined whether the physiological effects of high-amylose maize starch (HAMS) are influenced by hydroxypropylation. Rats were fed one of the following three diets: an AIN-93-based diet with waxy maize starch (WMS) as a starch source, or this diet with 150 g of WMS replaced by either HAMS or hydroxypropylated HAMS (HP-HAMS). The activities of amylase in bile-pancreatic juice and sucrose, maltase and isomaltase of the jejunum and ileum were not affected by diet, but the digestibility of HAMS was decreased by hydroxypropylation. The amounts of SCFA in caecal content and H2 excreted in the breath and flatus for HAMS were decreased by hydroxypropylation. Plasma glucagon-like peptide-1 (GLP-1), glucose and insulin concentrations were not affected by diet. On the basis of PCR-denaturing gradient gel electrophoresis (DGGE) profiles, the similarity in caecal bacteria population of the HP-HAMS group and HAMS group was low, but that of the HP-HAMS and WMS groups was high. The amount of caecal IgA was not affected by hydroxypropylation, but those in the HAMS and HP-HAMS groups were greater than that in the WMS group. Plasma and liver concentrations of TAG and cholesterol for HAMS were not affected by hydroxypropylation. These results show that the small intestinal digestibility and fermentation-dependent parameters such as caecal SCFA and H2 productions and caecal bacterial profile of HAMS were affected by hydroxypropylation, but parameters of glucose metabolism such as GLP-1 and insulin, those of lipid metabolism such as plasma TAG and cholesterol and the amount of caecal IgA were not.

Acute effects of continuous infusions of glucagon-like peptide (GLP)-1, GLP-2 and the combination (GLP-1+GLP-2) on intestinal absorption in short bowel syndrome (SBS) patients. A placebo-controlled study

BACKGROUND AND AIMS

The ileocolonic brake is impaired in short bowel syndrome (SBS) patients with distal bowel resections. An attenuated meal-stimulated hormone secretion may cause gastric hypersecretion, rapid gastric and intestinal transit and a poor adaptation. Attempting to restore this ileocolonic brake, this study evaluated the acute effects of continuous intravenous administration of glucagon-like peptide (GLP) 1 and 2, alone or in combination, on gastrointestinal function in SBS patients.

METHODS

SBS patients were admitted 4 times for identical 72-h balance studies, where infusions (1 pmol/kg/min) of GLP-1, placebo (saline), GLP-2 and GLP-1+2 (1 pmol/kg/min of each), were provided. Patients filled out a VAS questionnaire regarding subjective symptoms during treatments. Bone mineral content, body-weight and -composition were measured using DEXA scans. Blood glucose, insulin, pro insulin C-peptide and GLP concentrations were measured in relation to a standardized breakfast.

RESULTS

Nine SBS patients (5 women/4 men, aged 52±11) were enrolled and completed the study; 7 had end-jejunostomies, 2 had 50% of colon-in-continuity. All treatments significantly reduced the fecal wet weight, energy, nitrogen, sodium and potassium losses compared to placebo. However, only GLP-2 containing treatments increased absolute absorption of wet weight and sodium. Only GLP-1+2 improved the hydrational status evaluated by DEXA increases in the fat mass and calculated total body weight. GLP-1 and GLP-1+2 reduced the post-prandial blood glucose levels. A tendency of nausea and reduced appetite was seen in relation to GLP-1 treatment, but this was ameliorated by the co-administration of GLP-2.

CONCLUSION

GLP-1 decreased diarrhea and fecal excretions in SBS patients, but it seems less potent than GLP-2. The combination of GLP-1+2 numerically provided additive effects on intestinal absorption compared to either peptide given alone. Larger, long-term studies should further assess the potential of the glucagon-like peptides or analogs, alone or in combination, in the treatment of SBS patients.

Digestive physiology of the pig symposium: potential applications of knowledge of gut chemosensing in pig production

Pig production is a commodity business, which makes it a cost-driven business. Pig producers and their advisors are appropriately reluctant to adopt technologies without confidence that improved production will more than pay for the cost of the technology. Physiological effects of technologies targeting gut sensory pathways must translate to demonstrably improved health and/or productive performance if they are to be adopted. The types and degrees of stressors experienced by pigs in commercial production vary widely and often differ from those in research herds, and those variations influence their productive responses to nutritional and health technologies. Pigs are most vulnerable to disease soon after weaning, and the diets fed to pigs at that time are more expensive and offered in much smaller amounts than those fed later in life. Those factors make it easier to justify expensive dietary technologies for young pigs than for older ones. New developments in gut chemosensing appear important, but their practical application is not yet clear. We suggest investigation of the potential to connect chemical detection by the gut to pig productivity and/or efficiency through these mechanisms: 1) trophic effects on the intestines, which lead to improved enteric health or enhanced nutrient digestion and absorption, 2) enhanced barrier function in the intestinal mucosa, 3) increased feed intake, 4) enhanced insulin secretion and sensitivity, which may be especially useful in lactating sows to improve subsequent reproduction, and 5) other signals triggered by products of enteric fermentation, possibly short-chain fatty acids, that may influence gut integrity, feed intake, and reproductive function. Each of these mechanisms relates to a practical issue in pig production. Practical application would likely be achieved through dietary changes, but separate management factors, drugs, or other interventions may also be developed.

The role of peptide YY in gastrointestinal diseases and disorders (review)

Peptide YY (PYY) is affected in several gastrointestinal diseases and disorders. Changes in PYY appear to be an adaptive response to alterations in pathophysiological conditions caused by the disease. This applies to gastrointestinal diseases/disorders such as irritable bowel syndrome, inflammatory bowel disease, celiac disease, systemic sclerosis, and post-intestinal resection. By contrast, the changes in PYY in chronic idiopathic slow transit constipation (CST) seem to be of a primary nature, and may be one etiological factor of the disease. Abnormalities in PYY seem to contribute to the development of symptoms present in irritable bowel syndrome, inflammatory bowel disease, gastroenteropathy in long-standing diabetes and CST. The changes in PYY could, however, be favorable in some gastrointestinal disorders such as celiac disease, systemic sclerosis and post-intestinal resection state. Investigating changes in PYY in gastrointestinal diseases/disorders could be beneficial in clinical practice, where a receptor agonist or an antagonist can be used as a drug, depending on the condition. Similar to other neuroendocrine peptides/amines of the gut, PYY has broad physiological/pharmacological effects: it can bind to and activate several receptors with independent actions. Thus, in order to use PYY as a drug, receptor-specific agonists or antagonists need to be developed.

The effect of osmolarity and caloric load on small bowel motility

BACKGROUND

Although there is profound knowledge about cyclic fasting motility, the postprandial intestinal motor response is not well investigated. It is intriguing to speculate that nutrient composition alters small bowel motility significantly and, in a clinical setting, may account for adverse gastrointestinal symptoms in enteral nutrition (EN). We aimed to assess the impact of different caloric loads and osmolarities of EN on human jejunal motility.

METHODS

Sixteen healthy subjects underwent a series of duodenal infusions of EN solutions, either with iso-osmolar solution with different caloric loads (1.32, 2.64, or 3.96 kcal min(-1)), or with solutions of different osmolarities with constant caloric loads (300, 600, or 1200 mosmol). Jejunal solid-state manometry was analyzed over 90 min both visually and using dedicated computer software.

KEY RESULTS

All tested nutrient solutions were able to trigger conversion to a postprandial jejunal motility pattern after a mean lag phase of 9.4 + 2.3 min (P = NS between different nutrient solutions). Different caloric loads did not result in significant differences in small bowel motility. However, increasing osmolarities caused a significant inhibition of contractile and propagative activity.

CONCLUSIONS & INFERENCES

Small bowel motility under duodenal infusion of nutrient solutions is not influenced by caloric load in a physiological range, whereas high osmolarities inhibit small bowel motility.

Modulatory role of PYY in transport and metabolism of cholesterol in intestinal epithelial cells

Background

Gastrointestinal peptides are involved in modulating appetite. Other biological functions attributed to them include the regulation of lipid homeostasis. However, data concerning PYY remain fragmentary. The objectives of the study were: (i) To determine the effect of PYY on intestinal transport and synthesis of cholesterol, the biogenesis of apolipoproteins (apos) and assembly of lipoproteins and (ii) To analyze whether the effects of PYY are similar according to whether cells are exposed to PYY on apical or basolateral surface.

Methodology/Principal Findings

Caco-2/15 cells were incubated with PYY (1–36) administered either to the apical or basolateral medium, at concentrations of 50 or 200 nM for 24 hours. De novo synthesis of cholesterol, cholesterol uptake, and assembly of lipoproteins were evaluated through the incorporation of [¹⁴C]-acetate, [¹⁴C]-cholesterol, and [¹⁴C]-oleate, respectively. Biogenesis of apos (A-I, A-IV, E, B-48 and B-100) was examined by the incorporation of [³⁵S]-methionine. The influence of PYY on protein and mRNA levels of many key mediators of lipid metabolism was analyzed by Western blot and PCR, respectively. Our results show that PYY influenced cholesterol metabolism in Caco-2/15 cells depending on the site of PYY delivery. Apical addition of PYY significantly lowered the incorporation of [¹⁴C]-cholesterol likely via the reduction of NPC1L1, stimulated intracellular cholesterol synthesis probably through an increase in SREBP-2 expression, whereas it concomitantly increased apo A-I synthesis and decreased LDL secretion. In contrast, basolateral PYY reduced the production of chylomicrons (CM) as well as the biogenesis of apos B-48 and B-100, while lowering the expression of the transcription factors RXRα and PPAR(α,β).

Conclusions/Significance

PYY is capable of influencing cholesterol homeostasis in intestinal Caco-2/15 cells depending on the site delivery. Apical PYY was able to decrease cholesterol uptake via NPC1L1 downregulation, whereas basolateral PYY diminished CM output through the biogenesis decline of apos B-48 and B-100.

Role of Y(2) receptors in the regulation of gastric tone in rats

We set out to determine the effect of peptide YY(3-36) (PYY(3-36)) on the gastric muscle tone in conscious rats by measuring intragastric pressure (IGP) during intragastric nutrient drink infusion. After an overnight fast, a chronically implanted gastric fistula was connected to a custom-made nutrient drink infusion system and a catheter to measure IGP. IGP was measured before and during the infusion of a nutrient drink (Nutridrink; 0.5 ml/min) until 10 ml was infused. Rats were treated with PYY(3-36) (0, 33, and 100 pmol·kg(-1)·min(-1)) in combination with a subcutaneous injection of the Y(2) receptor antagonists JNJ31020028 (10 mg/kg) or BIIE0246 (2 mg/kg). Experiments were also performed after subdiaphragmatic vagotomy and after pretreatment with 3 ml of nutrient drink (to mimic a fed state). IGP was compared as the average IGP during nutrient infusion, represented as means ± SE and compared using ANOVA. PYY(3-36) dose dependently increased the IGP during nutrient infusion (4.7 ± 0.3, 5.7 ± 0.5 and 7.3 ± 0.7 mmHg; P < 0.01) while JNJ31020028 and BIIE0246 could block this increase [4.4 ± 0.5 (P < 0.001) and 4.8 ± 0.4 (P < 0.05) mmHg, respectively]. Also in vagotomized rats, PYY(3-36) was able to significantly increase the IGP during, an effect attenuated by JNJ31020028. BIIE0246 and JNJ31020028 were not able to decrease the IGP when no PYY(3-36) was administered. PYY(3-36) increased gastric tone through an Y(2) receptor-mediated mechanism that does not involve the vagus nerve. Y(2) receptor antagonists were not able to decrease gastric tone without exogenous administration of PYY(3-36), indicating that Y(2) receptors do not play a crucial role in the determination of gastric tone in physiological conditions.

Immunohistochemical study on the ontogenetic development of the regional distribution of peptide YY, pancreatic polypeptide, and glucagon-like peptide 1 endocrine cells in bovine gastrointestinal tract

The regional distribution and relative frequency of peptide YY (PYY)-, pancreatic polypeptide (PP)-, and glucagon-like peptide 1 (GLP-1)-immunoreactive (IR) cells were determined immunohistochemically in the gastrointestinal tract at seven ontogenetic stages in pre- and postnatal cattle. Different frequencies of PYY-, PP-, and GLP-1-IR cells were found in the intestines at all stages; they were not found in the esophagus and stomach. The frequencies varied depending on the intestinal segment and the developmental stage. The frequencies of PYY- and PP-IR cells were lower in the small intestine and increased from ileum to rectum, whereas GLP-1-IR cells were more numerous in duodenum and jejunum, decreased in ileum and cecum, and increased again in colon and rectum. The frequencies also varied according to pre- and postnatal stages. All three cell types were most numerous in fetus, and decreased in calf and adult groups, indicating that the frequencies of these three types of endocrine cells decrease with postnatal development. The results suggest that these changes vary depending on feeding habits and adaptation of growth, secretion, and motility of intestine at different ontogenetic stages of cattle.

Using the lymphatics to study nutrient absorption and the secretion of gastrointestinal hormones

The lymph fistula rat model has traditionally been used to study the intestinal absorption of nutrients, especially lipids, but recently this model has also been used for studying the secretion of incretin hormones by the small intestine. The small intestine is not only responsible for the digestion and transport of dietary triacylglycerol, through the formation of chylomicrons, but it also secretes the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) from enteroendocrine cells. Ultimately, both chylomicrons and incretins are found in lymph. Advantages of the lymph fistula rat model in studying chylomicron and incretin secretion are numerous and include: 1) the concentrations of incretin hormones are higher in lymph than in peripheral or portal plasma; 2) there is reduced degradation of incretin hormones by DPP-IV in the lymph compartment; 3) less dilution by the circulating fluid; 4) this model allows the continuous collection of lymph from conscious animals, eliminating any potential side effects on lymph flow and gastrointestinal function due to anesthesia; and finally, and perhaps most importantly, and 5) the concentration in the intestinal lymph provides a physiologically accurate representation of the hormonal milieu within the intestinal mucosa where incretins may interact with enteroendocrine and/or dendritic cells and signal through the enteric or autonomic neurons. The importance of GIP and GLP-1 in health and disease is becoming more apparent, especially as the prevalence of type 2 diabetes and other metabolic disorders increases. This review focuses on the use of the lymph fistula rat as a model to study the secretion of incretins, as well as dietary lipid.

Application of the lactose 13C-ureide breath test for measurement of equine orocaecal transit time

REASONS FOR PERFORMING STUDY

Application of the lactose (13) C-ureide breath test (LUBT) for measurement of equine orocaecal transit time (OCTT) has not been reported previously. The ability to assess OCTT noninvasively, and to investigate its relationship to gastric emptying rate and small intestinal transit, would be of both clinical and research value.

OBJECTIVES

1) Assessment of the LUBT in healthy horses, with comparison of induced versus noninduced test protocols. 2) Application of a new dual stable isotope breath test (lactose (13) C-ureide and (13) C-octanoic acid) for gastrointestinal transit measurement.

HYPOTHESIS

The LUBT will allow quantification of equine OCTT, and test efficacy will be enhanced by prior administration of lactose (12) C-ureide as shown in vitro. The dual tracer breath test will permit simultaneous measurement of gastric emptying, OCTT and small bowel transit times.

METHODS

Induced and noninduced LUBTs were performed in 3 healthy mature horses in randomised order using a standard test meal and protocol. Combined LUBT and (13) C-octanoic acid breath tests ((13) C-OABT) were performed in 4 individuals on 4 occasions at weekly intervals. Expiratory isotopic recovery was modelled to allow generation of gastric emptying data, small bowel transit times and caecal transit parameters.

RESULTS

The induction protocol for the LUBT increased the rate and magnitude of expiratory (13) CO(2) significantly. Mean ± s.d. values for OCTT, caecal lag phase (t(lag) ) and caecal t(1/2) using the induced LUBT were 3.24 ± 0.65 h, 5.62 ± 1.22 h and 6.31 ± 1.21 h, respectively. Dual stable isotope tests resulted in the production of 2 discrete peaks in expiratory (13) CO(2) in 15/16 tests from which gastric t(1/2), OCTT and small bowel transit (SBT) parameters could be calculated.

CONCLUSIONS

The induced LUBT provides a reliable noninvasive measure of equine OCTT and can be paired with the (13) C-OABT to provide further information about small intestinal motility.

Effects of acute dietary restriction on gut motor, hormone and energy intake responses to duodenal fat in obese men

BACKGROUND

Previous patterns of energy intake influence gastrointestinal function and appetite, probably reflecting changes in small-intestinal nutrient-mediated feedback. Obese individuals consume more fat and may be less sensitive to its gastrointestinal and appetite-suppressant effects than lean individuals.

OBJECTIVE

To evaluate the hypothesis that, in obese individuals, the effects of duodenal fat on gastrointestinal motor and hormone function, and appetite would be enhanced by a short period on a very-low-calorie diet (VLCD).

METHODS

Eight obese men (body mass index 34±0.6  kg  m(-2)) were studied on two occasions, before (V1), and immediately after (V2), a 4-day VLCD. On both occasions, antropyloroduodenal motility, plasma cholecystokinin (CCK), peptide-YY (PYY) and ghrelin concentrations, and appetite perceptions were measured during a 120-min intraduodenal fat infusion (2.86  kcal  min(-1)). Immediately afterwards, energy intake was quantified.

RESULTS

During V2, basal pyloric pressure and the number and amplitude of isolated pyloric pressure waves (PWs) were greater, whereas the number of antral and duodenal PWs was less, compared with V1 (all P<0.05). Moreover, during V2, baseline ghrelin concentration was higher; the stimulation of PYY and suppression of ghrelin by lipid were greater, with no difference in CCK concentration; and hunger and energy intake (kJ; V1: 4378±691, V2: 3634±700) were less (all P<0.05), compared with V1.

CONCLUSIONS

In obese males, the effects of small-intestinal lipid on gastrointestinal motility and some hormone responses and appetite are enhanced after a 4-day VLCD.

Lymphatics in intestinal transport of nutrients and gastrointestinal hormones

The lymph fistula rat has been used for studying intestinal absorption of nutrients, especially lipids. Lipid absorption begins with the digestion of triacylglycerol (TAG) to form 2-monoacylglycerol (2-MAG) and fatty acids (FA), which are then incorporated in bile salt-mixed micelles. The mixed micelles deliver these digestion products to enterocytes for uptake. There, 2-MAG and FA are re-esterified to form TAG, which is then incorporated into chylomicrons (CMs) to be carried by the lymphatic system. Coincident with CMs' secretion into lymph, the small intestine also secretes incretin hormones. Advantages of the lymph fistula model in studying CMs and incretin secretion include the following: (1) the animal being conscious, (2) much less dilution of CMs and incretins than in portal blood, and (3) fewer degrading enzymes than portal blood, e.g., dipeptidyl peptidase-IV. Examples of the lymph fistula model being used for studying CMs' transport in normal and pathophysiologic states are presented. Recently, the lymph fistula rat has also been used for studying the secretion of incretins by the small intestine.

Differential responses of the incretin hormones GIP and GLP-1 to increasing doses of dietary carbohydrate but not dietary protein in lean rats

Previous studies have shown that oral ingestion of nutrients stimulates secretion of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1); however, it is unclear whether there is a dose-dependent response between the amount of nutrient ingested and the secretion of the hormones in vivo. Using our lymph fistula rat model, we previously demonstrated that both GIP and GLP-1 responded dose dependently to increasing amounts of infused dietary lipid and that the GLP-1-secreting cells were more sensitive to changes in intestinal lipid content. In the present study, we investigated the dose-dependent relationships between incretin secretion and the two remaining macronutrients, carbohydrate and protein. To accomplish this objective, the major mesenteric lymphatic duct of male Sprague-Dawley rats was cannulated. Each animal received a single bolus (3 ml) of saline, dextrin, whey protein, or casein hydrolysate (0.275, 0.55, 1.1, 2.2, 4.4 kcal) via a surgically inserted duodenal or ileal feeding tube. Lymph was continuously collected for 3 h and analyzed for GIP and GLP-1 content. Both GIP and GLP-1 outputs responded dose dependently to increasing amounts of dietary carbohydrate but not protein. Additionally, we found that the GIP-secreting cells were more sensitive than the GLP-1-secreting cells to changes in intestinal carbohydrate content.

Postprandial changes in small bowel water content in healthy subjects and patients with irritable bowel syndrome

BACKGROUND & AIMS

Postprandial symptoms are common in patients with irritable bowel syndrome with diarrhea (IBS-D) and could be diet related. We studied postprandial changes in distribution of water in the upper gastrointestinal tract of healthy volunteers (HVs) and patients with IBS-D after contrasting meals.

METHODS

In study 1, 11 HVs consumed 350-mL test meals with 5% mannitol (unabsorbable) or 5% glucose (readily absorbed). In study 2, 17 HVs consumed a 331-kcal meal, with or without 15 g bran. In study 3, 26 patients with IBS-D consumed the study 2 diet with bran meal. All subjects underwent serial magnetic resonance imaging analysis.

RESULTS

In study 1, subjects' small bowel water content (SBWC) increased after the mannitol but not glucose meals, reaching 381 mL (interquartile range, 343-491 mL) and 47 mL (18-78 mL), respectively, 40 minutes after eating (P < .001). In study 2, SBWC initially decreased after both meal types and then increased, plateauing at 180-405 minutes and was greater after the bran meal (P = .02). In study 3, fasting and postprandial SBWC was lower in IBS-D than in HVs (P < .05 and P < .0001, respectively). Patients with IBS-D had faster orocecal transit times (135 minutes; 90-180 minutes) compared with HVs (225 minutes; 203-293 minutes; P < .0001) and reduced terminal ileum diameter (P < .003).

CONCLUSIONS

Postprandial SBWC initially decreases, because of rapid, nutrient-driven fluid absorption, and then increases after a mixed liquid/solid meal. Patients with IBS-D have reduced fasting and postprandial SBWC with faster transit, possibly indicating increased small intestinal tone.

Using the lymph fistula rat model to study incretin secretion

The past several decades have witnessed a flourish of interest in the field of incretin biology. The importance of the two incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), in health and disease is becoming more apparent as the prevalence of type 2 diabetes and other metabolic disorders escalates. Rodent models have become indispensable in the study of the physiological function of GIP and GLP-1; however, investigators have run into several roadblocks when untangling the regulation of incretin secretion in these systems. The low circulating levels of the incretin hormones combined with sensitivity of the currently available assays require substantial amounts of blood to be removed from an animal if the hormones are to be analyzed over a period of time. Because of these limitations, continuous monitoring of GIP and GLP-1 secretion becomes difficult. A more effective means of studying incretin secretion in small animal models is therefore desirable. This chapter evaluates the use of the lymph fistula rat as a model to study the secretion of incretins. Lymph fistula models, in a variety of animals, have been used for decades to study the absorption and transport of lipid and lipophilic compounds; however, only recently has the value of this model been appreciated as a tool to explore incretin secretion.

Mechanisms of gastric emptying disturbances in chronic and acute inflammation of the distal gastrointestinal tract

It is unclear why patients with inflammation of the distal bowel complain of symptoms referable to the upper gastrointestinal tract, specifically to gastric emptying (GE) disturbances. Thus we aimed to determine occurrence and putative pathomechanisms of gastric motor disorders in such patients. Thirteen healthy subjects (CON), 13 patients with Crohn's disease (CD), 10 with ulcerative colitis (UC), and 7 with diverticulitis (DIV) underwent a standardized (13)C-octanoic acid gastric emptying breath test. Plasma glucose, CCK, peptide YY, and glucagon-like peptide-1 (GLP-1) were measured periodically and correlated with GE parameters. Results were given in means +/- SD. Compared with CON, GE half time (T) was prolonged by 50% in CD (115 +/- 55 vs. 182 +/- 95 min, P = 0.037). Six CD, 2 DIV, and 2 UC patients had pathological T (>200 min). Postprandial plasma glucose was increased in all patients but was highest in DIV and correlated with T (r = 0.90, P = 0.006). In CD, mean postprandial CCK levels were increased threefold compared with CON (6.5 +/- 6.7 vs. 2.1 +/- 0.6 pmol/l, P = 0.027) and were correlated with T (r = 0.60, P = 0.041). Compared with CON, GLP-1 levels were increased in UC (25.1 +/- 5.2 vs. 33.5 +/- 13.0 pmol/l, P = 0.046) but markedly decreased in DIV (9.6 +/- 5.2 pmol/l, P < 0.0001). We concluded that a subset of patients with CD, UC, or DIV has delayed GE. GE disturbances are most pronounced in CD and might partly be caused by excessive CCK release. In DIV there might be a pathophysiological link between decreased GLP-1 release, postprandial hyperglycemia, and delayed GE. These explorative data encourage further studies in larger patient groups.

Stimulation of incretin secretion by dietary lipid: is it dose dependent?

After the ingestion of nutrients, secretion of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) by the enteroendocrine cells increases rapidly. Previous studies have shown that oral ingestion of fat stimulates secretion of both incretins; however, it is unclear whether there is a dose-dependent relationship between the amount of lipid ingested and the secretion of the hormones in vivo. Recently, we found a higher concentration of the incretin hormones in intestinal lymph than in peripheral or portal plasma. We therefore used the lymph fistula rat model to test for a dose-dependent relationship between the secretion of GIP and GLP-1 and dietary lipid. Under isoflurane anesthesia, the major mesenteric lymphatic duct of male Sprague-Dawley rats was cannulated. Each animal received a single, intraduodenal bolus of saline or varying amounts of the fat emulsion Liposyn II (0.275, 0.55, 1.1, 2.2, and 4.4 kcal). Lymph was continuously collected for 3 h and analyzed for triglyceride, GIP, and GLP-1 content. In response to increasing lipid calories, secretion of triglyceride, GIP, and GLP-1 into lymph increased dose dependently. Interestingly, the response to changes in intraluminal lipid content was greater in GLP-1- than in GIP-secreting cells. The different sensitivities of the two cell types to changes in intestinal lipid support the concept that separate mechanisms may underlie lipid-induced GIP and GLP-1 secretion. Furthermore, we speculate that the increased sensitivity of GLP-1 to intestinal lipid content reflects the hormone's role in the ileal brake reflex. As lipid reaches the distal portion of the gut, GLP-1 is secreted in a dose-dependent manner to reduce intestinal motility and enhance proximal fat absorption.

Effects of mid-jejunal compared to duodenal glucose infusion on peptide hormone release and appetite in healthy men

INTRODUCTION

Cells containing GIP and CCK predominate in the upper small intestine, while those containing GLP-1 are located more distally. Our aim was to compare the hormonal, glycemic and appetite responses to different sites of glucose delivery.

METHODS

Ten healthy males were each studied twice, in randomized order. A catheter was positioned with openings 15 cm beyond the pylorus ("duodenal"), and 100 cm beyond ("mid-jejunal"). On one day, glucose was infused into the duodenum (1 kcal/min) and saline into the mid-jejunum, for 90 min. On the other day, the infusion sites were reversed. Blood was sampled frequently, and hunger was scored by questionnaires. The tube was removed and energy intake measured from a buffet meal.

RESULTS

Stimulation of CCK and suppression of hunger were greater (each P<0.05), and energy intake less (P=0.05), with duodenal compared to mid-jejunal glucose infusion. Blood glucose, GIP, and insulin did not differ, and there was minimal GLP-1 increment on either day.

CONCLUSIONS

There is regional variation in CCK, but not incretin hormone release, in the upper small intestine, and modest differences in the site of glucose exposure affect appetite and energy intake.

Ileal brake: a sensible food target for appetite control. A review

With the rising prevalence of obesity and related health problems increases, there is increased interest in the gastrointestinal system as a possible target for pharmacological or food-based approaches to weight management. Recent studies have shown that under normal physiological situations undigested nutrients can reach the ileum, and induce activation of the so-called "ileal brake", a combination of effects influencing digestive process and ingestive behaviour. The relevance of the ileal brake as a potential target for weight management is based on several findings: First, activation of the ileal brake has been shown to reduce food intake and increase satiety levels. Second, surgical procedures that increase exposure of the ileum to nutrients produce weight loss and improved glycaemic control. Third, the appetite-reducing effect of chronic ileal brake activation appears to be maintained over time. Together, this evidence suggests that activation of the ileal brake is an excellent long-term target to achieve sustainable reductions in food intake. This review addresses the role of the ileal brake in gut function, and considers the possible involvement of several peptide hormone mediators. Attention is given to the ability of macronutrients to activate the ileal brake, and particularly variation attributable to the physicochemical properties of fats. The emphasis is on implications of ileal brake stimulation on food intake and satiety, accompanied by evidence of effects on glycaemic control and weight loss.

Gastrointestinal transit abnormalities are frequently detected in patients with unexplained GI symptoms at a tertiary centre

The aim of this prospective study was to analyse the yield and utility of a gastrointestinal (GI) transit measurement procedure in clinical practice. Patients referred by gastroenterologists to a tertiary centre for detailed transit measurements were prospectively included. All together 243 patients were enrolled. Body mass index was recorded. The patients were categorized according to the predominant symptom into five groups: diarrhoea, constipation, nausea, vomiting and abdominal pain. The patients recorded their bowel movements and GI symptoms daily during the week before the transit measurement. Percentiles 5 and 95 of the transit values in 83 healthy subjects served as reference values. Widespread abnormalities were found in the five patient groups and 63% of the patients had at least one transit abnormality. The abnormalities were more frequent in men compared with women. Patients with underweight had more motility disturbances compared with other patients. In male and female patients with vomiting a significant delay of transit in the ascending colon was observed compared with healthy subjects. Large-scale transit measurements frequently detect transit abnormalities in clinical practice and may elucidate the relationship between some GI symptoms and abnormal motility.

Review article: The gastrointestinal tract: neuroendocrine regulation of satiety and food intake

BACKGROUND

The gastrointestinal tract elicits numerous signals regulating food intake and satiety, and recently many studies have been performed to elucidate the mechanisms regulating these signals.

AIM

To describe the effects of the gastrointestinal tract on satiety, satiation and food intake.

METHODS

A PubMed search was performed to identify and select the relevant literature using search terms including 'gastric satiety, intestine + satiety, satiation, cholecystokinin, ghrelin, peptide YY, glucagon-like peptide-1 and ileal brake'.

RESULTS

Satiation, satiety and food intake result, among other factors, from signals originating in the stomach caused by distension and signals from the small intestine. These intestinal signals result from nutrient sensing in the gut and activate neural and humoral pathways. Activation of the distal part of the gut, the so called ileal brake, leads to reduction in hunger and food intake, and models of chronic ileal brake activation lead to massive weight loss.

CONCLUSION

Gastrointestinal signals are crucial for the regulation of food intake, satiety and satiation. The ileal brake deserves special attention, as both ileal intubation studies and surgical studies demonstrate that activation of the ileal brake reduces food intake. In the surgical models, weight loss occurs without adaptation to the anorectic effects of ileal brake activation.

Alteration of gastric functions and candidate genes associated with weight reduction in response to sibutramine

BACKGROUND & AIMS

It is unclear whether weight loss with the noradrenergic (norepinephrine) and serotonergic (5-hydroxytryptamine) reuptake inhibitor, sibutramine, is associated with altered stomach functions and whether genetics influence treatment response.

METHODS

Forty-eight overweight and obese but otherwise healthy participants were randomized to placebo or sibutramine (15 mg/day for 12 weeks). At baseline and posttreatment we measured the following: gastric emptying for solids and liquids by scintigraphy, gastric volumes by single-photon emission computed tomography, maximum tolerated volume and 30-minute postnutrient challenge symptoms, and selected gastrointestinal hormones. All participants received structured behavior therapy for weight management. The influence of candidate gene polymorphisms involved in norepinephrine and 5-hydroxytryptamine or receptor function (phenylethanolamine N-methyltransferase, guanine nucleotide binding protein beta polypeptide 3, alpha2A adrenoreceptor, and solute carrier family 6 [neurotransmitter transporter, serotonin] member 4 [homo sapiens] [SLC6A4]) on weight loss and gastric functions was evaluated.

RESULTS

The overall average weight loss posttreatment was 5.4 +/- 0.8 (SEM) kg with sibutramine and 0.9 +/- 0.9 kg with placebo (P < .001). The sibutramine group showed significant retardation in gastric emptying of solids (P = .03), reduced maximum tolerated volume (P = .03), and increased postprandial peptide YY compared with the placebo group. Obese females showed greater effects of sibutramine on weight loss and gastric emptying of solids and liquids. Gastric volumes and postchallenge symptoms were not significantly different in the 2 treatment groups. The LS/SS genotype of the promoter for SLC6A4 was associated with enhanced weight loss with sibutramine.

CONCLUSIONS

Weight reduction with sibutramine is associated with altered gastric functions and increased peptide YY and is significantly associated with SLC6A4 genotype. The role of genetic variation in SLC6A4 on weight loss in response to sibutramine deserves further study.

Bowel dysfunction after transposition of intestinal segments into the urinary tract: 8-year prospective cohort study

PURPOSE

Bowel function may be disturbed after intestinal segments are transposed into the urinary tract to reconstruct or replace the bladder. In 1997 our group was the first to report major bowel dysfunction in a cohort of such patients. Up to 42% of those who were asymptomatic preoperatively described new bowel symptoms postoperatively including explosive diarrhea, nocturnal diarrhea, fecal urgency, fecal incontinence and flatus leakage. We now describe bowel symptoms in this same cohort 8 years later (2005).

MATERIALS AND METHODS

A total of 116 patients were evaluable. Of the remaining 37 from the original study 30 had died, 5 no longer wished to be involved and 2 could not be located. Patients were asked to complete postal questionnaires identical to those used in the first followup, assessing the severity of bowel symptoms and quality of life using 2 validated instruments. Responses were compared with those from the original study. The Nottingham Health Profile quality of life scores were also compared to age and sex matched norms.

RESULTS

There were 96 patients (83%) who completed 8-year followup questionnaires, including 43 after ileal conduit diversion (group 1), 17 after clam enterocystoplasty for overactive bladder (group 2), 18 after bladder reconstruction for neurogenic bladder dysfunction (group 3) and 18 with bladder replacement for nonneurogenic causes (group 4). High prevalence rates of bowel symptoms persisted with no statistically significant differences between the 2 times. Of those with symptoms in 2005, approximately 50% had reported similar symptoms in 1997. Patients treated with clam enterocystoplasty (group 2) still reported the highest prevalence (59%) of troublesome diarrhea with 1 in 2 on regular antidiarrheal medication. They also had high rates of fecal incontinence (47%), fecal urgency (41%) and nocturnal bowel movement (18%), and a large number reported a moderate or severe adverse effect on work (36%), social life (50%) and sexual activity (43%). High rates were also reported by patients with neurogenic bladder dysfunction, including 50% with troublesome diarrhea. This symptom was reported by 19% after ileal conduit and by 17% after bladder replacement for nonneurogenic causes. The impact of bowel symptoms on everyday activities and quality of life persisted, remaining most severe after clam enterocystoplasty, with 24% regretting undergoing the procedure because of subsequent bowel symptoms.

CONCLUSIONS

After more than 8 years, operations involving transposition of intestinal segments continue to be associated with high rates of bowel symptoms which impact everyday activities. These are particularly troublesome following enterocystoplasty for overactive bladder and bladder reconstruction for neurogenic bladder dysfunction. These risks should influence patient selection and potential patients should be warned before undergoing surgery.

Ileal brake: neuropeptidergic control of intestinal transit

Digestion and absorption of a meal are time-intensive processes. To optimize digestion and absorption, transit of the meal through the gastrointestinal tract is regulated by a complex integration of neuropeptidergic signals generated as the jejunal brake and ileal brake response to nutrients. Mediators involved in the slowing of transit responses include peptide YY (PYY), chemosensitive afferent neurons, intestinofugal nerves, noradrenergic nerves, myenteric serotonergic neurons, and opioid neurons. The activation of this circuitry modifies the peristaltic reflex to convert the intestinal motility pattern from propagative to segmenting. Fat is the most potent trigger of these transit control mechanisms. The integrated circuitry of gut peptides and neurons involved in transit control in response to nutrients is described in this review.

Gastric sensorimotor functions and hormone profile in normal weight, overweight, and obese people

BACKGROUND & AIMS

Peptide YY (PYY) levels are reported to be decreased in obesity. The relation between gastric functions, satiation, and gut hormones in obesity is incompletely understood. The aim of this study was to compare gastric volumes, emptying, maximum tolerated volumes, postchallenge symptoms, and selected gut hormones in normal, overweight, or obese healthy volunteers.

METHODS

In 73 nonbulimic normal, overweight, or obese participants weighing less than 137 kg, we measured gastric emptying of solids and liquids by scintigraphy (gastric emptying half-time [GE t(1/2)]); gastric volumes by single-photon emission computed tomography; maximum tolerated volumes and symptoms by satiation test; and plasma leptin, ghrelin, insulin, glucagon-like peptide 1, and PYY levels. Groups were compared using 1-way analysis of covariance adjusted for sex. Univariate associations among measured responses were assessed using Spearman correlations. Multiple linear regression models, adjusting for weight and sex, assessed the independent ability of gastric functions and hormones to predict satiation volume.

RESULTS

Obese and overweight subjects had significantly lower postprandial gastric volumes, higher fasting and postprandial insulin and leptin levels, and lower fasting ghrelin and lower postprandial reduction in ghrelin levels. PYY levels were not different in obese or overweight subjects compared with controls. The GE t(1/2) was correlated inversely with postprandial PYY; increased body weight was associated with faster GE t(1/2) of solids (r(s) = 0.33, P = .005) and liquids (r(s) = 0.24, P = .04). Postprandial changes in gastric volume and PYY were independent predictors of satiation (both P = .01).

CONCLUSIONS

Overweight or obesity are associated with lower postprandial gastric volumes and normal PYY levels. Gastric emptying influences postprandial PYY levels. Postprandial PYY and gastric volume independently predict satiation volume in nonbulimic people across a wide body mass index range.