Gastric tone determines the sensitivity of the stomach to distention

Effect of intracolonic volume on gastric sensory-motor responses in constipation-predominant irritable bowel syndrome

BACKGROUND

Interaction between gut stimuli may induce symptom overlap in patients with functional gastrointestinal disorders. The aim is to determine the effect of increased volumes of colonic contents on gastric sensory/motor responses and satiety in patients with constipation-predominant irritable bowel syndrome (IBS-C) and overlapping dyspeptic symptoms, and a cohort of healthy subjects.

METHODS

In 15 patients with IBS-C and 10 healthy subjects, the effect of real versus sham colonic filling with gas (1080 ml) on gastric sensitivity (measured by stepwise distensions of the stomach), gastric compliance, abdominal perception, and nutrient drink tolerance was studied on separate days.

RESULTS

In healthy subjects, colonic gas filling induced an increment in gastric sensitivity to distension (mean score 2.0 ± 0.2 before, and 3.0 ± 0.4 after; p = 0.038). In IBS, basal sensitivity was greater and remained unchanged after colonic gas filling (score 4.0 ± 0.1 and 3.8 ± 0.3, respectively; p < 0.001 vs. basal in health). Colonic gas infusion induced abdominal symptoms that were significantly greater in IBS-C (score 2.6 ± 0.1) than in health (score 1.7 ± 0.4; p = 0.027), with minor changes in gastric tone, and no changes in gastric compliance in both groups. Colonic filling produced a profound reduction in nutrient drink tolerance in IBS (791 ± 87 ml sham filling, 491 ± 58 ml gas filling; p < 0.001) but only a minor reduction in health (940 ± 70 ml sham filling, 860 ± 94 ml gas filling; p = 0.223).

CONCLUSIONS & INFERENCES

The volume of the colonic contents modulates satiety in patients with IBS-C, due to a general visceral pan-hypersensitivity. These effects should be considered in the choice of treatment for constipation in these patients.

Gastrointestinal Contributions to the Postprandial Experience

Food ingestion induces homeostatic sensations (satiety, fullness) with a hedonic dimension (satisfaction, changes in mood) that characterize the postprandial experience. Both types of sensation are secondary to intraluminal stimuli produced by the food itself, as well as to the activity of the digestive tract. Postprandial sensations also depend on the nutrient composition of the meal and on colonic fermentation of non-absorbed residues. Gastrointestinal function and the sensitivity of the digestive tract, i.e., perception of gut stimuli, are determined by inherent individual factors, e.g., sex, and can be modulated by different conditioning mechanisms. This narrative review examines the factors that determine perception of digestive stimuli and the postprandial experience.

On a coupled electro-chemomechanical model of gastric smooth muscle contraction

The stomach is a central organ in the gastrointestinal tract that performs a variety of functions, in which the spatio-temporal organisation of active smooth muscle contraction in the stomach wall (SW) is highly regulated. In the present study, a three-dimensional model of the gastric smooth muscle contraction is presented, including the mechanical contribution of the mucosal and muscular layer of the SW. Layer-specific and direction-dependent model parameters for the active and passive stress-stretch characteristics of the SW were determined experimentally using porcine smooth muscle strips. The electrical activation of the smooth muscle cells (SMC) due to the pacemaker activity of the interstitial cells of Cajal (ICC) is modelled by using FitzHugh-Nagumo-type equations, which simulate the typical ICC and SMC slow wave behaviour. The calcium dynamic in the SMC depends on the SMC membrane potential via a gaussian function, while the chemo-mechanical coupling in the SMC is modelled via an extended Hai-Murphy model. This cascade is coupled with an additional mechano-electrical feedback-mechanism, taking into account the mechanical response of the ICC and SMC due to stretch of the SW. In this way the relaxation responses of the fundus to accommodate incoming food, as well as the typical peristaltic contraction waves in the antrum for mixing and transport of the chyme, have been well replicated in simulations performed at the whole organ level. STATEMENT OF SIGNIFICANCE: In this article, a novel three-dimensional electro-chemomechanical model of the gastric smooth muscle contraction is presented. The propagating waves of electrical membrane potential in the network ofinterstitial cells of Cajal (ICC) and smooth muscle cells (SMC) lead to a global pattern of change in the calciumdynamics inside the SMC. Taking additionally into account the mechanical response of the ICC and SMC due to stretch of the stomach wall, also referred to as mechanical feedback-mechanism, the result is a complex spatio-temporal regulation of the active contraction and relaxation of the gastric smooth muscle tissue. Being a firstapproach, in future view such a three-dimensional model can give an insight into the complexload transferring system of the stomach wall, as well as into the electro-chemomechanicalcoupling process underlying smooth muscle contraction in health and disease.

Status of Brain Imaging in Gastroparesis

The pathophysiology of nausea and vomiting in gastroparesis is complicated and multifaceted involving the collaboration of both the peripheral and central nervous systems. Most treatment strategies and studies performed in gastroparesis have focused largely on the peripheral effects of this disease, while our understanding of the central nervous system mechanisms of nausea in this entity is still evolving. The ability to view the brain with different neuroimaging techniques has enabled significant advances in our understanding of the central emetic reflex response. However, not enough studies have been performed to further explore the brain–gut mechanisms involved in nausea and vomiting in patients with gastroparesis. The purpose of this review article is to assess the current status of brain imaging and summarize the theories about our present understanding on the central mechanisms involved in nausea and vomiting (N/V) in patients with gastroparesis. Gaining a better understanding of the complex brain circuits involved in the pathogenesis of gastroparesis will allow for the development of better antiemetic prophylactic and treatment strategies.

Deoxycholic acid activates colonic afferent nerves via 5-HT3 receptor-dependent and -independent mechanisms

Increased bile acids in the colon can evoke increased epithelial secretion resulting in diarrhea, but little is known about whether colonic bile acids contribute to abdominal pain. This study aimed to investigate the mechanisms underlying activation of colonic extrinsic afferent nerves and their neuronal cell bodies by a major secondary bile acid, deoxycholic acid (DCA). All experiments were performed on male C57BL/6 mice. Afferent sensitivity was evaluated using in vitro extracellular recordings from mesenteric nerves in the proximal colon (innervated by vagal and spinal afferents) and distal colon (spinal afferents only). Neuronal excitability of cultured dorsal root ganglion (DRG) and nodose ganglion (NG) neurons was examined with perforated patch clamp. Colonic 5-HT release was assessed using ELISA, and 5-HT immunoreactive enterochromaffin (EC) cells were quantified. Intraluminal DCA increased afferent nerve firing rate concentration dependently in both proximal and distal colon. This DCA-elicited increase was significantly inhibited by a 5-HT₃ antagonist in the proximal colon but not in the distal colon, which may be in part due to lower 5-HT immunoreactive EC cell density and lower 5-HT levels in the distal colon following DCA stimulation. DCA increased the excitability of DRG neurons, whereas it decreased the excitability of NG neurons. DCA potentiated mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. Together, this study suggests that DCA can excite colonic afferents via direct and indirect mechanisms but the predominant mechanism may differ between vagal and spinal afferents. Furthermore, DCA increased mechanosensitivity of high-threshold spinal afferents and may be a mechanism of visceral hypersensitivity.NEW & NOTEWORTHY Deoxycholic acid (DCA) directly excites spinal afferents and, to a lesser extent, indirectly via mucosal 5-HT release. DCA potentiates mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. DCA increases vagal afferent firing in proximal colon via 5-HT release but directly inhibits the excitability of their cell bodies.

Prevalence and pathophysiology of post-prandial migraine in patients with functional dyspepsia

Background

Migraine is a condition frequently associated with gastrointestinal disorders. Previous reports have shown the relationship between irritable bowel syndrome and migraine, but no data are yet available in patients with functional dyspepsia. We therefore evaluated whether alteration of gastric sensorimotor activity may be related to migraine.

Methods

Sixty patients affected by functional dyspepsia, 38 with postprandial distress syndrome and 22 with epigastric pain syndrome were enrolled in a cohort study. Presence and severity of dyspeptic symptoms, migraine presence and severity, gastric sensitivity thresholds during fasting and postprandial period, gastric accommodation and gastric emptying time were evaluated.

Results

In epigastric pain syndrome, 12/22 (54%) patients suffered from migraine and this condition was never correlated with meal ingestion. In postprandial distress syndrome patients, 29/38 (76%) suffered from migraine, in 26/29 (89%) its onset was considered as meal-related, and migraine severity was significantly correlated with postprandial modification of the gastric discomfort threshold (r = −0.73; p < 0.001). In patients with postprandial distress syndrome, in the subgroup with moderate to severe migraine, the severity of fullness and early satiation was significantly higher than in patients with mild or absent migraine. In patients with moderate to severe migraine, gastric accommodation, sensitivity thresholds and gastric emptying time were similar to patients with mild or no migraine.

Conclusions

In patients with functional dyspepsia and postprandial symptoms, migraine is a very frequent comorbidity. On clinical grounds, it is associated with an increased severity of fullness and early satiation and, on pathophysiological grounds, it seems correlated with postprandial hypersensitivity.

Porcine Stomach Smooth Muscle Force Depends on History-Effects

The stomach serves as food reservoir, mixing organ and absorption area for certain substances, while continually varying its position and size. Large dimensional changes during ingestion and gastric emptying of the stomach are associated with large changes in smooth muscle length. These length changes might induce history-effects, namely force depression (FD) following active muscle shortening and force enhancement (FE) following active muscle stretch. Both effects have impact on the force generating capacity of the stomach, and thus functional relevance. However, less is known about history-effects and active smooth muscle properties of stomach smooth muscle. Thus, the aim of this study was to investigate biomechanical muscle properties as force-length and force-velocity relations (FVR) of porcine stomach smooth muscle strips, extended by the analysis of history-effects on smooth muscle force. Therefore, in total n = 54 tissue strips were dissected in longitudinal direction from the ventral fundus of porcine stomachs. Different isometric, isotonic, and isokinetic contraction protocols were performed during electrical muscle stimulation. Cross-sectional areas (CSA) of smooth muscles were determined from cryo-histological sections stained with Picrosirius Red. Results revealed that maximum smooth muscle tension was 10.4 ± 2.6 N/cm². Maximum shortening velocity (V_max) and curvature factor (curv) of the FVR were 0.04 ± 0.01 [optimum muscle length/s] and 0.36 ± 0.15, respectively. The findings of the present study demonstrated significant (P < 0.05) FD [up to 32% maximum muscle force (F_im)] and FE (up to 16% F_im) of gastric muscle tissue, respectively. The FE- and FD-values increased with increasing ramp amplitude. This outstanding muscle behavior is not accounted for in existing models so far and strongly supports the idea of a holistic reflection of distinct stomach structure and function. For the first time this study provides a comprehensive set of stomach smooth muscle parameters including classic biomechanical muscle properties and history-dependent effects, offering the possibility for the development and validation of computational stomach models. Furthermore, this data set facilitates novel insights in gastric motility and contraction behavior based on the re-evaluation of existing contractile mechanisms. That will likely help to understand physiological functions or dysfunctions in terms of gastric accommodation and emptying.

The NO/cGMP pathway in duodenal motor, mechano- and chemosensory responses to acid: A randomized, placebo-controlled study with sildenafil in healthy volunteers

BACKGROUND

Altered duodenal sensorimotor responses to acid have been reported in a subset of patients with functional dyspepsia. To investigate whether NO is involved in these abnormalities, the effect of sildenafil (activates the NO pathway) on duodenal motor and sensory responses to acid in healthy humans was evaluated.

METHODS

A barostat-manometry catheter including an infusion tube was positioned in the duodenum of 12 healthy volunteers. Duodenal motility and dyspeptic symptoms were evaluated during the whole study. A first series of stepwise isobaric distensions was performed while participants scored their perception of upper abdominal sensations at the end of every distension step. Next, the duodenum was infused with sildenafil 50 mg or saline, followed by duodenal acid infusion. During duodenal acidification, a second sequence of stepwise isobaric distensions with the assessment of sensations was repeated.

KEY RESULTS

Acid infusion did not induce dyspeptic symptoms with both placebo and sildenafil pretreatment. Duodenal motility decreased after sildenafil infusion, whereas it was not affected by placebo. Acid-induced increase in motility was, however, observed in both conditions, and no difference between the conditions was found. Duodenal acidification decreased thresholds for discomfort and increased perception scores during duodenal distensions in both groups, but again no difference was observed between placebo and sildenafil pretreatment.

CONCLUSIONS AND INFERENCES

Sildenafil does not affect duodenal motor, mechanosensory, and chemosensory responses to acid in healthy controls. Therefore, it is less likely that the NO pathway plays a role in the altered response to acid in functional dyspepsia patients.

Fundamentals of Neurogastroenterology: Physiology/Motility - Sensation

The fundamental gastrointestinal functions include motility, sensation, absorption, secretion, digestion and intestinal barrier function. Digestion of food and absorption of nutrients normally occurs without conscious perception. Symptoms of functional gastrointestinal disorders are often triggered by meal intake suggesting abnormalities in the physiological processes are involved in the generation of symptoms. In this manuscript, normal physiology and pathophysiology of gastrointestinal function, and the processes underlying symptom generation are critically reviewed. The functions of each anatomical region of the digestive tract are summarized. The pathophysiology of perception, motility, mucosal barrier, and secretion in functional gastrointestinal disorders as well as effects of food, meal intake and microbiota on gastrointestinal motility and sensation are discussed. Genetic mechanisms associated with visceral pain and motor functions in health and functional gastrointestinal disorders are reviewed. Understanding the basis for digestive tract functions is essential to understand dysfunctions in the functional gastrointestinal disorders.

Vagal Intramuscular Arrays: The Specialized Mechanoreceptor Arbors That Innervate the Smooth Muscle Layers of the Stomach Examined in the Rat

The fundamental roles that the stomach plays in ingestion and digestion notwithstanding, little morphological information is available on vagal intramuscular arrays (IMAs), the afferents that innervate gastric smooth muscle. To characterize IMAs better, rats were given injections of dextran biotin in the nodose ganglia, and, after tracer transport, stomach whole mounts were collected. Specimens were processed for avidin-biotin permanent labeling, and subsets of the whole mounts were immunohistochemically processed for c-Kit or stained with cuprolinic blue. IMAs (n = 184) were digitized for morphometry and mapping. Throughout the gastric muscle wall, IMAs possessed common phenotypic features. Each IMA was generated by a parent neurite arborizing extensively, forming an array of multiple (mean = 212) branches averaging 193 µm in length. These branches paralleled, and coursed in apposition with, bundles of muscle fibers and interstitial cells of Cajal. Individual arrays averaged 4.3 mm in length and innervated volumes of muscle sheet, presumptive receptive fields, averaging 0.1 mm(3) . Evaluated by region and by muscle sheet, IMAs displayed architectural adaptations to the different loci. A subset (32%) of circular muscle IMAs issued specialized polymorphic collaterals to myenteric ganglia, and a subset (41%) of antral longitudinal muscle IMAs formed specialized net endings associated with the serosal boundary. IMAs were concentrated in regional patterns that correlated with the unique biomechanical adaptations of the stomach, specifically proximal stomach reservoir functions and antral emptying operations. Overall, the structural adaptations and distributions of the IMAs were consonant with the hypothesized stretch receptor roles of the afferents.

Digestive, cognitive and hedonic responses to a meal

BACKGROUND

Gut dysfunctions may be associated to digestive symptoms. We hypothesized that the gut can also originate pleasant sensations, and wished to demonstrate the hedonic component of the digestive response to a meal.

METHODS

Healthy subjects (n = 42) were evaluated during basal fasting conditions and during experimentally induced fullness sensation (either by gastric distension or duodenal nutrient infusion). In each set of studies, a 240 mL test meal (12 kcal broth) and water, as inert control meal, were administered on separate days in a randomized, cross-over design. Gastric accommodation, the cognitive response and the hedonic dimension (both by 10 score scales) were measured 9 min before and 60 min after the meal.

KEY RESULTS

In basal conditions, the test meal induced a significantly greater gastric relaxation than the control meal (166 ± 28 mL isotonic volume increase 67 ± 14 mL; p = 0.002). Both meals induced epigastric fullness (3.8 ± 0.7 score and 3.2 ± 0.8 score, respectively; p = 0.740), but contrary to the inert meal, with the active meal this conscious sensation had a pleasant dimension (digestive comfort increase by 1.3 ± 0.6 score with active meal vs -1.1 ± 0.6 decrease with inert meal; p = 0.015). Experimentally induced fullness was associated to a decrease in digestive well-being or abdominal discomfort, which improved only after the active meal but not the inert meal.

CONCLUSIONS & INFERENCES

When appropriate conditions are met, the response to a meal includes a hedonic dimension involving pleasant sensation of digestive well-being.

Gastrointestinal dysfunction in liver cirrhosis

Patients with liver cirrhosis exhibit several features of gut dysfunction which may contribute to the development of cirrhosis complications as well as have an impact on nutritional status and health-related quality of life. Gastrointestinal symptoms are common in cirrhosis and their pathophysiology probably involves factors related to liver disease severity, psychological distress, and gut dysfunction (e.g., increased gastric sensitivity to distension and delayed gut transit). They may lead to reduced food intake and, thus, may contribute to the nutritional status deterioration in cirrhotic patients. Although tense ascites appears to have a negative impact on meal-induced accommodation of the stomach, published data on gastric accommodation in cirrhotics without significant ascites are not unanimous. Gastric emptying and small bowel transit have generally been shown to be prolonged. This may be related to disturbances in postprandial glucose, insulin, and ghrelin levels, which, in turn, appear to be associated to insulin resistance, a common finding in cirrhosis. Furthermore, small bowel manometry disturbances and delayed gut transit may be associated with the development of small bowel bacterial overgrowth. Finally, several studies have reported intestinal barrier dysfunction in patients with cirrhosis (especially those with portal hypertension), which is related to bacterial translocation and permeation of intestinal bacterial products, e.g., endotoxin and bacterial DNA, thus potentially being involved in the pathogenesis of complications of liver cirrhosis.

Fasting and postprandial gastric sensorimotor activity in functional dyspepsia: postprandial distress vs. epigastric pain syndrome

OBJECTIVES

Little information is available on the mechanisms responsible for dyspeptic symptoms in postprandial distress syndrome (PDS), characterized by the presence of prevalently meal-related early satiation and fullness, and the epigastric pain syndrome (EPS), characterized by the prominent symptom of epigastric pain, generally not meal related. In a group of PDS patients, the presence of hypersensitivity to gastric distension in both fasting and postprandial phases was described as the main pathophysiological mechanism; on the contrary, we have no information on the pathophysiology of EPS.

METHODS

Sixty Helicobacter pylori (HP)-negative, irritable bowel syndrome (IBS)-negative, and gastroesophageal reflux disease (GERD)-negative patients with functional dyspepsia according to Rome III criteria underwent symptom, anxiety, depression, and somatization evaluation, gastric barostat test, and gastric emptying time evaluation for solids. Fifteen age- and sex-matched healthy volunteers (HVs) were also enrolled as a control group.

RESULTS

In PDS patients, the prevalence of both fasting and postprandial hypersensitivity was higher than in EPS patients, and the extent of postprandial reduction of discomfort threshold was significantly correlated with symptom severity. In EPS patients, gastric volume at fasting discomfort threshold and fasting compliance were significantly lower than in PDS patients. Gastric emptying time and gastric accommodation were similar between the two dyspeptic groups. Dyspeptic patients showed a higher prevalence of psychiatric disorders than HVs, but the prevalence was similar between PDS and EPS patients.

CONCLUSIONS

Fasting and postprandial hypersensitivity characterize PDS patients and a reduction of gastric compliance is present in EPS patients. However, the pathophysiology of EPS appears more complex than PDS and further studies are needed to analyze central processing and integration of afferent pathways in order to clarify the role of the central nervous system in this condition.

Gastroduodenal mechanisms underlying functional gastric disorders

Functional dyspepsia (FD), a disorder thought to originate from the gastroduodenum, is one of the most prevalent functional gastrointestinal disorders. In this review, we focused on gastroduodenal mechanisms involved in the pathophysiology of FD. The roles of impaired gastric accommodation, delayed gastric emptying, hypersensitivity to gastric distention and to luminal agents, altered mucosal integrity, low-grade inflammation and psychological stress are reviewed. The underlying pathophysiology in FD is probably multifactorial, involving a combination of several of these factors, ultimately leading to symptom pattern and severity.

Gastric sensitivity and reflexes: basic mechanisms underlying clinical problems

Both reflex and sensory mechanisms control the function of the stomach, and disturbances in these mechanisms may explain the pathophysiology of disorders of gastric function. The objective of this report is to perform a literature-based critical analysis of new, relevant or conflicting information on gastric sensitivity and reflexes, with particular emphasis on the comprehensive integration of basic and clinical research data. The stomach exerts both phasic and tonic muscular (contractile and relaxatory) activity. Gastric tone determines the capacity of the stomach and mediates both gastric accommodation to a meal as well as gastric emptying, by partial relaxation or progressive recontraction, respectively. Perception and reflex afferent pathways from the stomach are activated independently by specific stimuli, suggesting that the terminal nerve endings operate as specialized receptors. Particularly, perception appears to be related to stimulation of tension receptors, while the existence of volume receptors in the stomach is uncertain. Reliable techniques have been developed to measure gastric perception and reflexes both in experimental and clinical conditions, and have facilitated the identification of abnormal responses in patients with gastric disorders. Gastroparesis is characterised by impaired gastric tone and contractility, whereas patients with functional dyspepsia have impaired accommodation, associated with antral distention and increased gastric sensitivity. An integrated view of fragmented knowledge allows the design of pathophysiological models in an attempt to explain disorders of gastric function, and may facilitate the development of mechanistically orientated treatments.

Bloating and distention in irritable bowel syndrome: the role of gas production and visceral sensation after lactose ingestion in a population with lactase deficiency

OBJECTIVES

Bloating and distention are often attributed to dietary factors by patients with irritable bowel syndrome (IBS). This study examined the effects of gas production and visceral hypersensitivity on digestive symptoms after lactose ingestion in a population with lactase deficiency.

METHODS

IBS patients (n=277) and healthy controls (HCs, n=64) underwent a 20-g lactose hydrogen breath test (LHBT) with evaluation of hydrogen gas production and lactose intolerance (LI) symptoms. Abdominal distention (199 IBS, 40 HCs) was measured during LHBT. Rectal sensitivity (74 IBS, 64 HCs) was assessed by barostat studies.

RESULTS

Hydrogen production and distention were similar in IBS patients and HCs during LHBT; however, LI was more frequent in IBS (53.8 vs. 28.1%, P<0.001), especially bloating (39.0% vs. 14.1%, P<0.001) and borborygmi (39.0 vs. 21.9%, P=0.010). Only 59.0% of patients with bloating had distention. No correlation was observed between girth increment and bloating (P=0.585). IBS patients had lower rectal sensory thresholds (P=0.001). Multivariate analysis indicated that hydrogen production increased bloating (odds ratio (OR) 2.19, 95% confidence interval (CI) 1.09-4.39, P=0.028) and borborygmi (OR 12.37, 95% CI 3.34-45.83, P<0.001) but not distention (P=0.673). Visceral hypersensitivity was associated with bloating (OR 6.61, 95% CI 1.75-25.00, P=0.005) and total symptom score (OR 3.78, 95% CI 1.30-10.99, P=0.014).

CONCLUSIONS

Gas production and visceral hypersensitivity both contribute to digestive symptoms, especially bloating and borborygmi, in IBS patients after lactose ingestion. Objective abdominal distention is not correlated with subjective bloating.

Role of duodenal mucosal nerve endings in the acid-induced duodenogastric sensorimotor reflex: effect of benzocaine in healthy humans

BACKGROUND

Duodenal acid exposure induces a duodenogastric reflex resulting in gastric relaxation, inhibition of antral motility, and sensitization of the proximal stomach to distension. Duodenal hypersensitivity to acid has been identified as a potential pathogenic mechanism in functional dyspepsia. The nature and localization of the duodenal acid-sensitive receptors are still elusive. We hypothesize that acid directly activates superficial afferent nerve endings in the duodenal mucosa, triggering the duodenogastric reflex.

METHODS

In a double-blind, randomized, crossover study in 13 healthy volunteers, benzocaine, a local anesthetic, vs saline was perfused in the duodenum 15 min before duodenal acid perfusion. Gastric responses were monitored by a barostat. Stepwise isobaric gastric distensions were performed before and during acid perfusion. Symptoms were evaluated by visual analogue scales for six dyspeptic symptoms and an overall perception score.

KEY RESULTS

Benzocaine perfusion caused a relaxation of the stomach prior to duodenal acidification, indicating the existence of an excitatory duodenogastric tone. Pretreatment of the duodenum with benzocaine reduced the acid-induced gastric relaxation by 50% and abolished the inhibition of phasic motility of the proximal stomach. Finally, sensitization to distension was more pronounced in the benzocaine condition because of higher proximal gastric volumes.

CONCLUSIONS & INFERENCES

These findings support a model in which different neuronal subpopulations are responsible for the motor and sensory limb of the acid-sensitive duodenogastric reflex, making benzocaine an unsuitable drug to treat duodenal hypersensitivity to acid. These data provide more insight in the contribution of duodenal neuronal input to gastric physiology in the fasting state.

The hypersensitivity to colonic distension of IBS patients can be transferred to rats through their fecal microbiota

BACKGROUND

Alterations of intestinal microbiota and hypersensitivity to colonic distension are two features of the irritable bowel syndrome (IBS). However, the role of intestinal microbiota in visceral hypersensitivity of IBS patients is far to be established. The aim of our study was to determine whether the intestinal microbiota is involved in the visceral hypersensitivity in IBS.

METHODS

The painful response to colorectal distension and colonic mucosal parameters were assessed in gnotobiotic rats. Germfree (GF) rats were inoculated with the fecal microbiota from IBS patients characterized by hypersensitivity to colorectal distension (IBS HMA rats) or from non-hypersensitive healthy volunteers (Healthy HMA rats). Conventional rats were studied as normosensitivity control. Fecal microbial analyses were carried out in human and HMA rats fecal samples using cultural and molecular approaches.

KEY RESULTS

The microbial dysbiosis of the IBS gut microbiota (more sulfate-reducing bacteria and Enterobacteriaceae and less bifidobacteria) could be maintained in gnotobiotic rats. The number of abdominal contractions in response to colorectal distensions was significantly higher in IBS HMA rats than in healthy HMA rats. No difference was observed between healthy HMA and conventional rats. Colorectal compliance, epithelial paracellular permeability, and density of colonic mucosal mast cells were similar in the three groups of rats.

CONCLUSIONS & INFERENCES

We herein showed that sensitivity to colonic distension of IBS patients can be transferred to rats by the fecal microbiota. Mucosal alterations associated with microbiota transfer are not involved in this hypersensitivity. The altered IBS microbiota may have important role in the hypersensitivity characterizing IBS patients through specific bacterial metabolites.

Abdominal accommodation induced by meal ingestion: differential responses to gastric and colonic volume loads

BACKGROUND

Using an experimental model of colonic gas infusion, we previously showed that the abdominal walls adapt to its content by an active phenomenon of abdominal accommodation. We now hypothesized that abdominal accommodation is a physiological phenomenon, and aimed to confirm that it can be induced by ingestion of a meal; a secondary aim was to determine whether the response to gut filling is region-specific.

METHODS

In healthy subjects (n = 24) a nutrient test meal was administered until tolerated at a rate of 50 mL min(-1). Electromyographic (EMG) activity of the anterior wall (upper and lower rectus, external and internal oblique) was measured via four pairs of surface electrodes, and EMG activity of the diaphragm via intraluminal electrodes on an esophageal tube. To address the secondary aim, the response to gastric filling was compared with that induced by colonic filling (1440 mL 30 min(-1) anal gas infusion; n = 8).

KEY RESULTS

Participants tolerated 927 ± 66 mL of meal (450-1500 mL). Meal ingestion induced progressive diaphragmatic relaxation (EMG reduction by 16 ± 2%; P < 0.01) and selective contraction of the upper abdominal wall (24 ± 2% increase in activity of the upper rectus and external oblique; P < 0.01 for both), with no significant changes in the lower rectus (4 ± 2%) or internal oblique (5 ± 3%). Colonic gas infusion induced a similar response, but with an overall contraction of the anterior wall.

CONCLUSIONS & INFERENCES

Meal ingestion induces a metered and region-specific response of the abdominal walls to accommodate the volume load. Abnormal abdominal accommodation could be involved in postprandial bloating.

Effect of the GLP-1 analog liraglutide on satiation and gastric sensorimotor function during nutrient-drink ingestion

BACKGROUND/AIM

Liraglutide, a glucagon-like peptide-1 analog, induces weight loss. We investigated whether liraglutide affects gastric accommodation and satiation by measuring the intragastric pressure (IGP) during nutrient-drink consumption and using the barostat technique.

METHODS

Ten healthy volunteers (HVs) were tested after placebo, 0.3, 0.6 or 1.2 mg liraglutide administration. IGP was studied during intragastric nutrient-drink (1.5 kcal ml(-1)) infusion (60 ml min(-1)), while the HVs scored their satiation on a graded scale until maximal satiation. In a separate session, isobaric distentions were performed using the barostat with stepwise increments of 2 mm Hg starting from minimal distending pressure, although HVs scored their perception; gastric volume was monitored 30 min before and until 60 min after ingestion of 200 ml of nutrient drink. Data are presented as mean±s.e.m. comparisons were performed with ANOVA (P<0.05 was significant).

RESULTS

During nutrient-drink infusion, IGP decreased with 4.1±0.7, 3.0±0.4, 2.1±0.3 and 2.6±0.4 mm Hg (placebo, 0.3, 0.6 and 1.2 mg liraglutide, respectively; P<0.05). The maximum-tolerated volume was not different, except after treatment with 1.2 mg liraglutide (695±135 ml) compared with placebo (1008±197 ml; P<0.05); however, 1.2 mg liraglutide induced nausea in all volunteers. In the barostat study, liraglutide did not affect the perception or compliance, but significantly decreased gastric accommodation to the meal (168±27 vs 78.8±36.4 ml after treatment with placebo and 0.6 mg liraglutide, respectively; P<0.05).

CONCLUSION

Although no effect on perception, compliance or satiation was observed, liraglutide inhibited gastric accommodation. Whether this effect is involved in the anorectic effect of liraglutide remains to be determined.

The effects of sildenafil on rectal sensitivity and tone in patients with the irritable bowel syndrome

BACKGROUND

Visceral tone supposedly affects gut sensitivity in irritable bowel syndrome (IBS). Sildenafil increases nitric oxide and influences visceral compliance.

AIM

To evaluate the effects of sildenafil tone inhibition on rectal sensitivity.

METHODS

Eight controls and 21 IBS patients (Rome II) were enrolled in a double-blind study, after dosing with placebo or sildenafil (50 mg p.o.). Thresholds for first sensation, first desire to defecate, pain and supraliminar pain were the sensory endpoints, measured with a barostat and 600-mL rectal bag. Pain (100-mm VAS) and depression-anxiety (Hamilton questionnaire) were scored.

RESULTS

Irritable bowel syndrome rectal compliance and sensory-endpoint thresholds were similar to controls. Five IBS patients had pain threshold lower than controls 95% confidence interval (hypersensitive). Depression score was greater in IBS than controls (11.9 ± 1.3 vs. 6.3 ± 2.5, P = 0.036). In IBS, pain intensity was nonsignificantly higher (37.6 ± 5.3 mm vs. 23.4 ± 8.5 mm, P = 0.064) and supraliminar pain intensity was greater (45.6 ± 5.4 mm vs. 25.9 ± 5.1 mm, P = 0.044) than controls. IBS rectal relaxation increased volume (155.4 ± 41.3 mL vs. 118.8 ± 47.7 mL, P = 0.004) and tension (193.1 ± 118.6 mmHg mL(-1) vs. 133.2 ± 98.1 mmHg mL(-1) , P = 0.019) for triggering first desire to defecate but not for other perceptions. Sildenafil increased volume for both first desire to defecate and pain in the hypersensitive IBS patients. Sildenafil increased rectal compliance only in diarrhoea-IBS. Mixed-IBS obtained higher anxiety (12.9 ± 1.3 vs. 5.9 ± 3.1, P < 0.05) and depression scores (13.9 ± 1.9 vs. 6.3 ± 2.5, P < 0.05) and reported more intense supraliminar pain (53.6 ± 9.8 mm vs. 25.9 ± 5.1 mm, P < 0.05) than controls.

CONCLUSIONS

Rectal relaxation following dosing with sildenafil 50 mg increased the first desire to defecate threshold in IBS as a whole, but decreased pain only in the hypersensitive subset. Mixed-IBS presented higher supraliminar pain and anxiety-depression scores.

Colonic hypersensitivity is a major determinant of the efficacy of bloating treatment in constipation-predominant irritable bowel syndrome

The pathophysiology of bloating is largely unknown, and many mechanisms have been proposed. An alteration of intestinal gas production may have a role in a subgroup of patients, but available data are conflicting. We have previously shown that hypersensitivity to colonic fermentation is associated with severe bloating in a subgroup of patients with low intestinal gas production. Accordingly, we evaluated whether modification of intestinal gas production improves bloating severity according to the presence of visceral hypersensitivity to colonic fermentation. Twenty-four IBS-C patients with severe bloating underwent intestinal gas production measurement by hydrogen breath test after lactulose, and a recto-sigmoid barostat test in order to evaluate sensitivity thresholds in a basal condition and after induction of colonic fermentation. The subjects were then randomly assigned to receive either rifaximin or placebo according to a double-blind, randomized, cross-over trial. Rifaximin induced an improvement of symptom severity. A post hoc analysis according to the presence of hypersensitivity to colonic fermentation shows that rifaximin induces a significant improvement in symptom severity only in normosensitive, hyperproducer patients. Modulation of colonic flora, in order to reduce fermentation, does not interfere with bloating severity in patients with visceral hypersensitivity, thus suggesting that in this subgroup of subjects gas production is not crucial for the onset of bloating.

Influence of ondansetron on gastric sensorimotor responses to short duodenal acid infusion in healthy volunteers

BACKGROUND

Duodenal acid infusion induces gastric relaxation and sensitization to distension in healthy volunteers. The acid-sensitive mechanism is still unknown. We hypothesized that 5HT(3)-blockade can inhibit the acid-induced duodenogastric sensorimotor reflex in healthy volunteers.

METHODS

Fourteen healthy volunteers were included in a randomized, double-blind placebo-controlled cross-over trial. An infusion tube with attached pH-electrode was positioned in the duodenum and a barostat balloon was located in the gastric fundus. Proximal gastric volume and sensitivity to distension were assessed before and during duodenal acid infusion and after pretreatment with intravenous (i.v.) ondansetron (a 5HT(3)-receptor antagonist, 8 mg) or saline. An overall perception score (0-6) and an assessment of nine dyspeptic symptoms by visual analogue scales (VAS) were obtained. Results are given as mean ± SEM.

KEY RESULTS

Ondansetron had no effect on duodenal pH and on the acid-induced increase of proximal gastric volume (increase of 80 ± 20 vs 83 ± 15 mL after ondansetron and placebo; effect of acid <0.001, between treatments ns). After ondansetron, the overall perception score during duodenal acidification and gastric distension was significantly decreased compared with placebo (P=0.01). There was no effect of ondansetron on the individual dyspeptic symptoms.

CONCLUSIONS & INFERENCES

Ondansetron decreased gastric sensitivity during duodenal acid infusion and gastric distension. 5HT(3)-receptors are involved in acid-induced duodenogastric sensitization, but not in the duodenogastric inhibitory motor reflex.

Quantification of the effects of the volume and viscosity of gastric contents on antral and fundic activity in the rat stomach maintained ex vivo

AIMS

The aim of this study was to examine the effect of varying the rheological properties of perfusate on the volume and muscular activity of the various compartments of the rat stomach.

METHODS

Image analysis was used to quantify the activity of the ex vivo stomach preparations when perfused according to a ramp profile.

RESULTS

The area of the fundus increased to a greater extent than that of the body when watery or viscous material was perfused. However, initial distension of the corpus was greater and occurred more rapidly when viscous material was perfused. Only the fundus expanded when perfusion followed the administration of verapamil. The frequency of antrocorporal contractions decreased significantly and the amplitude of antrocorporal contractions increased significantly with increase in gastric volume. The velocity of antrocorporal contractions did not vary with gastric volume but varied regionally in some preparations being faster distally than proximally. Neither the frequency, amplitude or velocity of antrocorporal contractions differed when pseudoplastic rather than watery fluid was perfused. However, the characteristics of antrocorporal contractions changed significantly when the stomach was perfused with material with rheological characteristics that induce different patterns of wall tension to those normally encountered. Hence, the mean frequency and speed of propagation of antrocorporal contractions increased and their direction of propagation became inconstant.

Intestinal immune activation in presumed post-infectious functional dyspepsia

Functional dyspepsia (FD) symptoms may develop after an acute gastroenteritis. In post-infectious (PI) irritable bowel syndrome, persisting low-grade colonic inflammation and increased enterochromaffine cells (EC) counts have been reported. The aim was to compare signs of inflammation and EC hyperplasia on duodenal biopsies in presumed PI-FD and unspecified-onset (U-)FD. Duodenal biopsies were obtained in 12 U-FD and 12 PI-FD (on average 13 months after the acute event) patients. The presence of intra-epithelial, intravillar, and the number of CD3, CD4, CD8 and CD68+ cells per crypts, and the mean number of Chromogranine A (CA) positive cells per villus were compared. We also measured gastric emptying and assessed proximal stomach function with a barostat. Data are shown as mean +/- SEM. Focal aggregates of T cells and focal CD8+ aggregates, were found in PI-FD but not in U-FD patients (respectively 5/12 vs 0/12, P = 0.02 and 5/9 vs 0/11, P < 0.01). In patients with focal aggregates, gastric emptying was delayed (189 +/- 37 min vs 98 +/- 11 min, P = 0.002). The number of CD4+ cells per crypt (0.52 +/- 1.6 vs 1.22 +/- 2.18, P = 0.04), and the number of intravillar CD4+ cells (0.5 +/- 0.2 vs 2.7 +/- 0.7, P = 0.01) were reduced, while the number of CD68+ cells per crypt was increased (0.64 +/- 0.13 vs 0.40 +/- 0.05, P = 0.03) in PI-FD. The number of EC and CA were comparable. PI-FD is associated with persisting focal T-cell aggregates, decreased CD4+ cells and increased macrophage counts surrounding the crypts. This may indicate impaired ability of the immune system to terminate the inflammatory response after acute insult.

Characterization of gastric volume responses and liquid emptying in functional dyspepsia and health by MRI or barostat and simultaneous C-acetate breath test

The assessment of gastric accommodation and emptying by different methodologies provides inconsistent results. We aimed to compare magnetic resonance imaging (MRI), barostat and 13C-acetate breath test (BT) for the assessment of gastric volume responses and emptying in healthy controls (HC) and patients with functional dyspepsia (FD). Eight HC and eight FD patients underwent: (i) continuous BT with simultaneous MRI in the upright position after ingestion of isocaloric, 300 kcal, 200 and 800 mL meals, both labelled with 100 mg of (13)C-acetate; and (ii) BT with gastric barostat after ingestion of the 200 mL meal. MRI measured total gastric volume and gastric content volume (GCV) at baseline, after filling and during emptying. Meal emptying half-times (T(1/2)) for MRI and BT were calculated (mean +/- SD). We found: (i) Initial GCV was lower in FD than in HC (762 +/- 22 vs 810 +/- 52 mL, P < 0.04) after the 800 mL meal but not the 200 mL meal. T(1/2)(MRI) was shorter for the 800 mL than the 200 mL meal (P < 0.001), but similar in HC and FD (200 mL: HC 117 +/- 30 min vs FD 138 +/- 42 min, ns; 800 mL: HC 71 +/- 16 min vs FD 78 +/- 27 min, ns). In contrast, T(1/2)(BT) was similar between meals and groups (200 mL: HC 111 +/- 11 min vs FD 116 +/- 19 min; 800 mL: HC 114 +/- 14 min vs FD: 113 +/- 17 min). (ii) Barostat measurements showed similar postprandial volume increases between groups. We conclude that direct measurements by MRI provide a sensitive, non-invasive assessment of gastric accommodation and emptying after a meal. In contrast to MRI, BT did not detect faster emptying of high-volume compared to low-volume liquid nutrient meals in HC or FD.

A placebo-controlled trial of the 5-HT1A agonist R-137696 on symptoms, visceral hypersensitivity and on impaired accommodation in functional dyspepsia

Acute studies suggested a therapeutic benefit for fundus-relaxing drugs in functional dyspepsia (FD) with visceral hypersensitivity (VH) to gastric distention or impaired accommodation (IA), but long-term studies are lacking. R-137696 is a serotonin-1A (5-HT(1A)) receptor agonist which relaxes the proximal stomach in man. Our aim was to investigate the influence of R-137696 on symptoms in FD with VH or IA. Randomized, double-blind, placebo-controlled, parallel group study of 4 weeks R-137696 2 mg t.i.d. in FD with VH or IA. Symptoms were assessed using the patient assessment of upper gastrointestinal symptom severity index (PAGI-SYM) total score and individual symptom subscales. Barostat studies were performed before and after 4 weeks of treatment. Fifty-three patients (33 VH and 20 IA), 18 men, mean age 40 +/- 13 years were recruited. Twenty-four received placebo and 29 received R-137696. In VH patients, both placebo and R-137696 improved total symptom scores, with a tendency for superiority of placebo (-1.12 vs-0.51, P = 0.07). Placebo was superior for the subscales of early satiety, bloating, fullness and discomfort (all P < 0.05). In IA, both placebo and R-137696 had no significant influence on total or individual symptom scores (-0.08 and -0.27). In VH, both placebo and R-137696 increased the discomfort volume, without a statistical difference between both arms (+120 and +164 mL). In IA, both placebo and R-137696 enhanced accommodation, without a statistical difference between both (+77 and +159 mL). Adverse events were similar for drug and placebo. A 4-week administration of the fundus-relaxing 5-HT(1A) agonist R-137696 failed to significantly improve symptoms, VH or gastric accommodation compared to placebo.

A dose-ranging, placebo-controlled, pilot trial of Acotiamide in patients with functional dyspepsia

Impaired gastric accommodation, hypersensitivity to distension and delayed gastric emptying are major pathophysiological mechanisms in functional dyspepsia (FD). Acotiamide (Z-338) was well-tolerated in healthy volunteers. To determine the effect of three doses of Acotiamide on major pathophysiological mechanisms, symptoms, quality of life (QOL) and safety in functional dyspeptics. A phase IIa, randomized, double-blind, placebo-controlled study (14, 21 and 28 days, respectively, for run-in, study drug administration and follow-up). Gastric accommodation, sensitivity to distension and gastric emptying were assessed by barostat and (13)C breath test, symptoms by daily diary cards and QOL by SF-36. A total of 71 patients were enrolled (62 evaluable). There was no effect on gastric emptying and sensitivity to distension. 300 mg was better than placebo for meal accommodation (P = 0.024). 100 mg was better than placebo at week 2 for upper abdominal bloating (P = 0.001) and overall symptom score (P = 0.022), and at week 3 for bloating (P = 0.008) and heartburn (P = 0.041). 100 mg was also better than placebo for QOL (physical function) (P = 0.003). Acotiamide was safe and well-tolerated in patients with FD. The involved mechanism could at least in part depend on an effect on meal-induced accommodation. 100 mg Acotiamide exhibited the potential to improve FD symptoms and QOL. Further studies are indicated.

Effects of remifentanil on gastric tone

OBJECTIVES

Opioids are well known for impairing gastric motility. The mechanism is far from clear and there is wide interindividual variability. The purpose of this study was to evaluate the effect of remifentanil on proximal gastric tone.

MATERIALS AND METHODS

Healthy volunteers were studied on two occasions and proximal gastric tone was measured by a gastric barostat. On the first occasion (n=8), glucagon 1 mg IV was given as a reference for a maximal relaxation of the stomach. On the second occasion (n=9), remifentanil was given in incremental doses (0.1, 0.2 and 0.3 microg/kg/min) for 15 min each, followed by a washout period of 30 min. Thereafter, remifentanil was readministered, and 10 min later glucagon 1 mg was given. Mean intragastric bag volumes were calculated for each 5-min interval.

RESULTS

Glucagon decreased gastric tone in all subjects. Remifentanil had a marked effect on gastric tone; we found two distinct patterns of reactions with both increases and decreases in gastric tone and, during the remifentanil infusion, glucagon did not affect gastric tone.

CONCLUSIONS

Remifentanil induced changes in gastric tone with both increases and decreases. The effect of remifentanil on gastric tone is probably dependent on the current state of the systems involved.

Visceral hypersensitivity and intolerance symptoms in lactose malabsorption

Lactose malabsorption is not always associated with intolerance symptoms. The factors responsible for symptom onset are not yet completely known. As differences in visceral sensitivity may play a role in the pathogenesis of functional symptoms, we evaluated whether an alteration of visceral sensitivity is present in subjects with lactose intolerance. Thirty subjects, recruited regardless of whether they were aware of their capacity to absorb lactose, underwent an evaluation of intestinal hydrogen production capacity by lactulose breath test, followed by an evaluation of lactose absorption by hydrogen breath test after lactose administration and subsequently an evaluation of recto-sigmoid sensitivity threshold during fasting and after lactulose administration, to ascertain whether fermentation modifies intestinal sensitivity. The role of differences in gastrointestinal transit was excluded by gastric emptying and mouth-to-caecum transit time by (13)C-octanoic and lactulose breath tests. Lactulose administration induced a significant reduction of discomfort threshold in subjects with lactose intolerance but not in malabsorbers without intolerance symptoms or in subjects with normal lactose absorption. Perception threshold showed no changes after lactulose administration. Severity of symptoms in intolerant subjects was significantly correlated with the reduction of discomfort thresholds. Visceral hypersensitivity should be considered in the induction of intolerance symptoms in subjects with lactose malabsorption.

Assessment of gastric sensorimotor function in paediatric patients with unexplained dyspeptic symptoms and poor weight gain

Recent studies indicate that impaired meal accommodation or hypersensitivity to distention are highly prevalent in adult functional dyspepsia (FD). Our aim was to investigate whether similar abnormalities also occur in paediatric FD. Sixteen FD patients (15 girls, 10-16 years) were studied. The severity (0-3; 0, absent; 3, severe) of eight dyspeptic symptoms (epigastric pain, fullness, bloating, early satiety, nausea, vomiting, belching and epigastric burning) and the amount of weight loss were determined by questionnaire. All children underwent a gastric barostat study after an overnight fast to determine sensitivity to distention and meal-induced accommodation, which were compared with normal values in young adults (18-22 years). On a separate day, all patients underwent a gastric emptying breath test. A mean weight loss of 4.8 +/- 0.9 kg was present in 14 children. Compared with controls, patients had lower discomfort thresholds to gastric distention (8.8 +/- 1.0 mmHg vs 13.9 +/- 1.9 mmHg, P < 0.02) and gastric accommodation (87 +/- 25 mL vs 154 +/- 20 mL P < 0.04). Hypersensitivity to distention and impaired accommodation were present in respectively nine (56%) and 11 (69%) patients. No relationship was found between barostat and gastric emptying, which was delayed in only three patients. The majority of children with unexplained epigastric symptoms have abnormalities of gastric sensorimotor function.

Role of gastric sensorimotor dysfunction in gastrointestinal symptoms and energy intake in liver cirrhosis

OBJECTIVE

Altered gastric sensorimotor function is related to the symptomatology in several gastrointestinal diseases. Gastrointestinal symptoms in patients with cirrhosis may result in low energy intake contributing to malnutrition and increased morbidity. The aim of this study was to investigate gastric accommodation to a meal and sensitivity to gastric distension with reference to energy intake, nutritional status and gastrointestinal symptoms in liver cirrhosis.

MATERIAL AND METHODS

Sixteen patients with cirrhosis and 15 healthy controls underwent a gastric barostat study to assess gastric accommodation to a meal and sensory thresholds for first perception and discomfort. The patients also underwent a slow caloric satiety drinking test. Food intake and nutritional status were also evaluated and gastrointestinal symptoms were assessed by means of a questionnaire.

RESULTS

Compared with controls, patients with cirrhosis had enhanced gastric accommodation (p<0.05) but lower daily energy intake (p<0.05). Patients with versus those without compromised nutritional status had enhanced gastric accommodation (p<0.05). Gastric accommodation was correlated to daily energy intake in controls (r=0.67, p<0.05) but not in cirrhotic patients (p>0.4). The end-point of the satiety test was inversely related to gastric volumes in cirrhotic patients. Mean post-meal balloon volumes were positively correlated to the Model for End Stage Liver Disease (MELD) score (r=0.53, p<0.05). Sensory thresholds did not differ between patients and controls but were related to gastrointestinal symptom severity and cirrhosis severity scores in the patients.

CONCLUSIONS

Gastric accommodation is increased in cirrhotic patients but there seems to be some disturbance in its relation to energy intake. The satiety drinking test is not a good surrogate marker of accommodation in cirrhotic patients. In cirrhosis the severity of gastrointestinal symptoms is related to gastric sensitivity.

Contribution of sensitivity, volume and tone to visceral perception in the upper gastrointestinal tract in man: emphasis on testing

Upper gastrointestinal (GI) symptoms occur frequently in the general population, making them among the most common indications responsible for patients consulting the healthcare system. Consequently, understanding and characterization of the upper GI symptoms is important for the diagnosis and assessment of organ dysfunction. In practice, assessment of clinical symptoms is difficult and it is still to a large extent unclear how sensitivity, volume and tone contribute to visceral perception in the upper GI tract. The goal of advanced research in upper GI symptoms is to obtain a better understanding of the mechanisms involved in transduction, transmission, and perception under normal and pathophysiological conditions. An important step towards this goal is understanding the information provided by and the inherent limitations of the currently available measuring techniques. This article focuses on the sensory testing of the oesophagus, and methods and concepts used to assess the relation between gastric volumes or tone and upper GI symptoms. It also summarizes the contributions of these techniques towards identifying the components responsible for the generation of upper GI symptoms.

Nutrient-dependent enhancement of rectal sensitivity in irritable bowel syndrome (IBS)

Food-related gastrointestinal symptoms are common in irritable bowel syndrome (IBS), but the mechanisms behind this are unclear. Enhanced colorectal sensitivity after duodenal lipid administration in IBS patients has been demonstrated. However, the effects of a regular meal on colorectal sensitivity in these patients and the importance of the composition of the meal are not known. On two separate days, 10 IBS patients and 11 controls randomly received a liquid meal (800 kcal), containing 60% calories from fat (fatty meal) or carbohydrate (carbohydrate meal). Using a barostat rectal sensitivity was assessed during four separate distension sequences before, immediately after and 30 and 60 min after the meal. In the patients, the discomfort (P = 0.04) and the pain thresholds (P = 0.007) were gradually reduced after the fatty meal, whereas only a tendency in the same direction was seen after the carbohydrate meal. In patients VAS ratings for pain increased after the fatty meal (P = 0.03), but not after carbohydrates. In the controls, sensory thresholds were not affected by the meals. In IBS, a liquid meal enhances rectal sensitivity, and this seems to be partly nutrient dependent as a fatty meal has more pronounced effects than a carbohydrate meal. This might be of relevance for their postprandial symptoms.

Role of colonic fermentation in the perception of colonic distention in irritable bowel syndrome and functional bloating

BACKGROUND & AIMS

Bloating represents a frequent gastrointestinal symptom, but the pathophysiologic mechanism responsible for its onset is still largely unknown. Patients very frequently attribute the sensation of bloating to the presence of excessive bowel gas, but not all patients with gas-related symptoms exhibit increased intestinal production of gas. It is therefore possible that other still unrecognized mechanisms might contribute to its pathophysiology. Our aim was to evaluate whether a subgroup of patients affected by functional abdominal bloating presents hypersensitivity to colonic fermentation.

METHODS

Sixty patients affected by functional gastrointestinal disorders (11 functional bloating, 36 constipation-predominant, and 13 diarrhea-predominant irritable bowel syndrome) and moderate to severe bloating took part in the study. Twenty sex- and age-matched healthy volunteers were enrolled as a control group. All the subjects underwent a preliminary evaluation of breath hydrogen excretion after oral lactulose. Then, on a separate day, an evaluation of sensitivity thresholds at rectal level was performed with a barostat before and after the induction of colonic fermentation with oral lactulose. A control test with electrolyte solution was also performed.

RESULTS

Both breath hydrogen excretion and mouth-to-cecum transit time did not differ between the 4 groups studied. Neither electrolyte solution nor lactulose modified sensitivity thresholds in healthy volunteers. In low hydrogen producers, basal perception and discomfort thresholds were similar to high hydrogen producers, but after lactulose both perception and discomfort thresholds were significantly reduced only in low hydrogen producers.

CONCLUSIONS

A subgroup of patients with functional gastrointestinal disorders and moderate to severe bloating might have hypersensitivity to products of colonic fermentation.

The influence of the novel 5-HT1A agonist R137696 on the proximal stomach function in healthy volunteers

As fundic dysaccommodation represents one of the pathophysiological mechanisms underlying functional dyspepsia, gastric relaxant agents may serve as a new treatment of this disorder. Previous studies have suggested the involvement of 5HT1 receptors in the control of gastric tone. Our aim was to study the effect of R137696, a novel 5HT1A agonist, on fundus sensorimotor function in healthy volunteers. The effect of single oral doses (1-2 mg) R137696 was evaluated in a double-blind, placebo-controlled manner on fasting fundic volume, visceral perception, distension-evoked symptoms and fundic compliance in 21 healthy male subjects. R137696 increased the proximal stomach volumes in a dose-dependent manner. Distention-evoked symptoms or distention and discomfort threshold were not altered by R137696. A logistic regression model, characterizing the relationships between the volume and the visual analogue scale score for dyspeptic symptoms (nausea, fullness, discomfort, pain and satiety) as a sigmoidal curve, revealed that R137696 had no effect on distension-induced discomfort, fullness, pain and satiety compared to placebo. R137696 relaxes the gastric fundus in fasting conditions but has no effect on distension-evoked dyspeptic symptoms in healthy volunteers.

Influence of delaying gastric emptying on meal-related symptoms in healthy subjects

BACKGROUND

Although delayed gastric emptying is often found in functional dyspepsia, a causal role for delayed emptying in inducing symptoms has not been demonstrated.

AIM

To investigate the influence of delaying gastric emptying rate in healthy volunteers on the occurrence of meal-related symptoms.

METHODS

Fourteen healthy subjects (six men, mean age 23 +/- 1) underwent gastric emptying studies twice using the 14C octanoic acid and 13C glycin breath test after pre-treatment with saline or sumatriptan 6 mg s.c. Breath samples were taken before meal and at 15-min intervals for a period of 360 min postprandially. At each breath sampling, the subject was asked to grade the intensity (0-6) of four dyspeptic symptoms.

RESULTS

Sumatriptan pre-treatment significantly delayed solid but not liquid gastric emptying (t1/2 respectively 159 +/- 11 vs. 112 +/- 9 min, P < 0.005 and 134 +/- 11 vs. 116 +/- 12 min, N.S.). Sumatriptan significantly decreased the mean cumulative symptom score (21.3 +/- 5.5 vs. 8.0 +/- 2.6, P = 0.01), as well as scores for each individual symptom.

CONCLUSION

A moderate delay in gastric emptying in health is not associated with an increase of meal-related symptoms. This observation argues against a causal role for delayed gastric emptying in the pathogenesis of dyspeptic symptoms.

Review article: a critical view on impaired accommodation as therapeutic target for functional dyspepsia

Several important pathophysiological mechanisms have been identified in functional dyspepsia, however a complete understanding of these mechanisms and beneficial therapeutic strategies are still lacking. Based on the currently available literature we aimed at providing a critical view on one of these pathophysiological mechanisms, impaired accommodation. Although impaired gastric accommodation is identified as a major pathophysiological mechanism, the clinical evidence supporting its role as an important therapeutic target is currently still lacking. Treatment with fundic relaxant drugs has shown conflicting results and has been rather disappointing in general. These negative findings could be explained by the fact that impaired fundic accommodation is part of a more complex disorder involving other regions of the proximal gut or by the increasing insight that central mechanisms may play an important role. Future studies of impaired accommodation should take these considerations into account.

Gastric compliance in bulimia nervosa

Bulimia nervosa (BN) is a psychiatric illness characterized by eating binges followed by inappropriate behavioral attempts to compensate for the binges, usually vomiting or laxative abuse. Patients with BN have disturbances in the development of satiety during a meal as well as disturbances in functions of the upper gastrointestinal tract such as slowed gastric emptying, impaired gastric accommodation reflex and blunted cholecystokinin release. The present study examined gastric compliance and sensory responses to gastric distention in women with BN and controls. Sixteen women with BN and 13 healthy control subjects swallowed an inflatable bag that was placed in the proximal stomach. The bag was inflated to produce increasing steps of pressure against the stomach wall, before and after consumption of a 200 ml (200 Kcal) liquid meal. Pressure and volume were recorded for 2-min periods, beginning at 0 mm Hg pressure and increasing in steps of 2 mm Hg until subjects reported discomfort, gastric volume reached 600 ml, or pressure reached 20 mm Hg. At each pressure step subjects made sensory ratings. Gastric compliance was calculated as the slope of the best-fit straight line of each subject's gastric volume vs. gastric pressure. There was a significant postmeal increase in gastric compliance in both groups of subjects but there was no difference in compliance between patients with BN and controls. Patients with BN appeared to have diminished sensitivity to gastric distention. In conclusion, although other studies have described gastrointestinal abnormalities associated with BN, the current study found gastric compliance of patients with BN to be normal.

Association of the predominant symptom with clinical characteristics and pathophysiological mechanisms in functional dyspepsia

BACKGROUND & AIMS

Functional dyspepsia (FD) is considered a heterogeneous disorder with different pathophysiological mechanisms contributing to the symptom pattern. The Rome II committee proposed that subdividing patients with FD into groups with predominant pain versus discomfort might identify subgroups with homogeneous pathophysiological and clinical properties. The aim of this study was to analyze the relationship of predominant pain or discomfort with pathophysiological mechanisms and to evaluate whether considering individual predominant symptoms yields better results.

METHODS

Consecutive FD patients (n = 720; 489 women; mean age, 41.3 +/- 0.6 years) filled out a dyspepsia questionnaire and identified a single most bothersome symptom. We analyzed the association of this predominant symptom with demographic, clinical, and pathophysiological features (Helicobacter pylori status, gastric emptying in 592 patients, and gastric sensitivity and accommodation testing in 332 patients).

RESULTS

According to Rome II criteria, 22% were pain predominant and 78% discomfort predominant. Patients with predominant pain had a higher prevalence of hypersensitivity (44% vs 25%) and delayed gastric emptying was observed less frequently in these patients (16% vs 26%), but there was major overlap. Detailed analysis showed that any of 8 dyspeptic symptoms could be predominant. Predominant early satiety or vomiting was associated with significantly higher prevalences of weight loss (89% and 75%, respectively) and of acute onset (61% and 60%, respectively). Impaired accommodation was found in 79% of patients with predominant early satiety. The highest prevalence of delayed emptying was found in predominant fullness (38%) and of hypersensitivity in predominant pain (44%).

CONCLUSIONS

Subdividing FD patient groups according to the predominant symptom does not reliably identify subgroups with a homogeneous underlying pathophysiological mechanism.

Modulation of gastric accommodation by duodenal nutrients

AIM: To determine the relative potency and contribution of intestinal nutrients to net gastric accommodative relaxation and conscious perception.

METHODS: In 12 healthy subjects, we randomly tested duodenal loads of lipids and carbohydrates (12 mL administered in 4 min) at various caloric concentrations (0.0125-0.8 kcal/mL) separated by 12-24 min wash-out periods of saline infusion. Maximal gastric relaxation was induced at the end of each experiment by i.v glucagon (5 µg/kg), as reference. The reflex gastric response was measured by a barostat, and symptom perception by a 0-6 score questionnaire.

RESULTS: Lipids induced a dose-response gastric relaxation with a steep and early rise. Maximal effect (179±42 mL relaxation) reached at a relatively low concentration (0.2 kcal/mL), maximal lipid-induced relaxation was 61±6% of the glucagon effect. By contrast, duodenal infusion of carbohydrates induced weaker relaxation that became significant only at the high end of the physiological concentration range (65±14 mL with 0.8 kcal/mL). Intestinal nutrient loads, either of lipid or carbohydrates, did not induce significant changes in perception (0.6±0.4 and 0.1±0.4 score increase for the highest concentrations, respectively).

CONCLUSION: Chyme entering the small bowel induces nutrient-specific gastric relaxatory reflexes by a physiologically saturable mechanism. Normally, neither the intestinal nutrient load nor the gastric accommodative response is perceived.

Intestinal perception: mechanisms and assessment

Physiological stimuli in the gut induce regulatory reflexes to accomplish the digestive process, but are normally not perceived. However, under some circumstances, gut stimuli may activate perception pathways and induce conscious sensations. Experimental evidence gathered during the past decade suggests that patients with functional gut disorders and unexplained abdominal symptoms may have a sensory dysfunction of the gut, so that physiological stimuli would induce symptoms. Assessment of visceral sensitivity is still poorly developed, but in analogy to somatosensory testing, differential stimulation of visceral afferents may be achieved by a combination of stimulation techniques, which may help to characterize sensory dysfunctions. Visceral afferent input is modulated by a series of mechanisms at different levels of the brain-gut axis, and conceivably, a dysfunction of these regulatory mechanisms could cause hyperalgesia. The sensory dysfunction in functional patients seems to be associated with altered reflex activity, and both mechanisms may interact to produce the symptoms. Evidence of a gut sensory-reflex dysfunction as a common pathophysiological mechanism in different functional gastrointestinal disorders would suggest that they are different forms of the same process, and that the clinical manifestations depend on the specific pathways affected.

Mechanoreceptors of the proximal stomach and perception of gastric distension

OBJECTIVES

To assess the role of tension receptors in gastric perception by pharmacologically modifying gastric contractile activity during isovolumetric distensions of the proximal stomach with the hypothesis that relaxation decreased perception and contraction increased it.

METHODS

Fourteen healthy subjects underwent two 30-min isovolumetric (75% of the threshold volume for discomfort) distensions using a barostat. During the second distension, either gastric relaxation was induced by intravenous (i.v.) glucagon 4.8 microg/kg bolus plus 9.6 microg/kg per h or contraction by i.v. erythromycin 3 mg/kg. Hunger and fullness were assessed with a 100-mm analog scale before and at 15 and 30 min during each distension.

RESULTS

Glucagon decreased baseline intrabag pressure (8.4 +/- 1.0 vs 10.7 +/- 1.3 mmHg; p < 0.05) and abolished the pressure waves (0 vs 16.7 +/- 2.3) when compared with placebo, whereas erythromycin increased baseline pressure (13.2 +/- 1.0 vs 11.9 +/- 0.9 mmHg; p < 0.05) and the rate of pressure waves (31.7 +/- 5.4 vs 20.5 +/- 3.1; p < 0.05). Fullness increased (p < 0.05) during distension, but it was unaffected by either of the drugs: Delta score (i.e., score during distension--baseline score) of 38 +/- 10 mm (glucagon) versus 22 +/- 10 (placebo) and 24 +/- 17 mm (erythromycin) versus 36 +/- 14 (placebo) at 15 min. Similar observation were made at 30 min. Hunger was influenced neither by distension nor by any of the two drugs consistently.

CONCLUSIONS

Our data do not support a prominent role of tension receptors of the proximal stomach on perception of fullness, suggesting that stretch, that is, volume, is the more relevant stimulus.

The physiological role of GLP-1 in human: incretin, ileal brake or more?

The proglucagon-derived peptide glucagon-like peptide-1 (GLP-1) is an intestinal signal peptide postprandially released from the L cells of the lower gut. Exogenously administered the synthetic hormone exerts a glucose-dependent insulinotropic effect at the pancreatic beta-cells and lowers plasma glucagon by an inhibitory effect against the alpha-cells. It delays gastric emptying by relaxation of the gastric fundus, inhibition of antral contractility, and stimulation of both the tonic and phasic motility of the pyloric sphincter. Enhancement of insulin, suppression of glucagon, and inhibition of gastric emptying are the main determinants controlling glucose homeostasis with GLP-1. Human studies employing the specific GLP-1 receptor antagonist exendin(9-39) show that endogenously released GLP-1 likewise controls fasting plasma glucagon, stimulates insulin, and influences all the motoric mechanisms known to control gastric emptying. Therefore, GLP-1 is discussed as an incretin hormone and as an enterogastrone in man. Synthetic GLP-1 also suppresses gastric acid and pancreatic enzyme secretion. The inhibitory effects on upper gastrointestinal functions are at least partly mediated by vagal-cholinergic inhibition and may involve interactions with vagal afferent pathways and/or circumventricular regions within the CNS. GLP-1 is a candidate humoral mediator of the 'ileal brake' exerting inhibition of upper gastrointestinal function preventing malabsorption and postprandial metabolic disturbances. As human studies indicate a central action of GLP-1 in reduction of food intake, it is uncertain if this is a consequence of induction of satiety or of transduction of visceral aversive stress signals.

Regional brain activation during proximal stomach distention in humans: A positron emission tomography study

BACKGROUND & AIMS

Hypersensitivity to proximal gastric distention due to abnormal central nervous system processing of visceral stimuli has been suggested as a possible underlying pathophysiologic mechanism in functional dyspepsia. However, the cortical regions activated by distention of the proximal stomach have not been identified. The aim of this study was to investigate regional brain activation during painful and nonpainful proximal gastric distention in humans.

METHODS

Positron emission tomography of the brain was performed in 11 healthy volunteers during 4 conditions: (1) no distention and isobaric distention to the individual thresholds for (2) first, (3) marked, and (4) unpleasant sensation. Data were analyzed using statistical parametric mapping.

RESULTS

During maximal distention relative to baseline, significant (P corrected <.05) regional brain activation occurred in the left and right gyrus postcentralis (Brodmann area [BA] 43), the left gyrus temporalis superior (BA 38), the right gyrus frontalis inferior (BA 47, orbitofrontal cortex), the right midanterior cingulate gyrus (BA 24), the right anterior insula, and the left cerebellar hemisphere. These areas showed a progressive increase in activation with increasing intensity of the distending stimulus.

CONCLUSIONS

We found evidence for a neuronal network processing distention stimuli of the proximal stomach that is overall consistent with the "visceral stimulation network" described in the literature. In addition, we found activation of the orbitofrontal cortex, confirming its role as a convergence zone for processing of food-related stimuli and regulation of hunger, appetite, satiety, and food intake. We found no evidence for a functional neuroanatomic divergence in the processing of noxious and innocuous gastric stimuli.

Influence of sildenafil on gastric sensorimotor function in humans

After a meal, the proximal stomach relaxes probably through the activation of nitrergic neurons in the gastric wall. Nitric oxide-induced smooth muscle relaxation involves activation of soluble guanylate cyclase, with cGMP production, which is then degradated by phosphodiesterase-5 (PDE-5). The aim of this study was to investigate the effect of sildenafil, a selective PDE-5 inhibitor, on fasting and postprandial proximal gastric volume and on gastric emptying rates in humans. A gastric barostat was used to study gastric compliance and perception to isobaric distension in healthy subjects before and after placebo (n = 13) or sildenafil, 50 mg (n = 15). In 10 healthy subjects, two gastric barostat studies were performed in randomized order to study the effect of placebo or sildenafil on postprandial gastric relaxation. Similarly, solid and liquid gastric emptying rates were studied in 12 healthy subjects. Sildenafil significantly increased fasting intragastric volume (141 +/- 15 vs. 163 +/- 15 ml, P < 0.05) and volumes of first perception. Sildenafil induced a higher and prolonged gastric relaxation either at 30 min (357 +/- 38 vs. 253 +/- 42 ml, P < 0.05) or 60 min (348 +/- 49 vs. 247 +/- 38 ml, P < 0.05) after the meal. Sildenafil did not alter solid half-emptying time but significantly delayed liquid emptying (43 +/- 4 vs. 56 +/- 4 min, P < 0.01). In conclusion, sildenafil significantly increases postprandial gastric volume and slows liquid emptying rate, confirming that meal-induced accommodation in humans involves the activation of a nitrergic pathway. The effect of sildenafil on gastric fundus suggests a therapeutic potential for phosphodiesterase inhibitors in patients with impaired gastric accommodation.

5-HT7 receptor efficacy distribution throughout the canine stomach

This study aimed to determine, quantify and explain regional differences in the relaxant response to the selective 5-HT(1) and 5-HT(7) receptor agonist 5-carboxamidotryptamine (5-CT) throughout the canine stomach. Longitudinal muscle strips from eight gastric corpus regions and six antrum regions were mounted for isotonic measurement. The 5-CT-induced relaxation was examined on a prostaglandin F(2alpha)-induced submaximal response, expressed as percentage of this response and fitted to the operational model of agonism (OMOA). 5-HT(7) receptor messenger RNA (mRNA) expression was compared by means of quantitative PCR. 5-CT inhibited PGF(2alpha)-induced tonic contraction (corpus) and increase of phasic contraction amplitude (antrum). The consistent antagonism produced by the selective 5-HT(7) receptor antagonist SB-269970 (10 nm, pA(2) estimates 8.2-8.9) confirmed that in every region, the inhibition by 5-CT was 5-HT(7) receptor mediated. However, variation in the maximum effect (61-108%) and pEC(50) (6.4-8.6) was observed throughout the different regions. The OMOA explained these differences as differences in the efficacy parameter tau (ratio of receptor density and coupling efficiency; log tau estimates ranging from 0.1 to 2.1). The log tau gradient decreases going from the lesser to the greater curvature. A proportional difference (68%) in the relative expression of 5-HT(7) receptor mRNA between the lesser and the greater curvature indicates that differences in receptor density contribute to the observed functional differences. This study illustrates that 5-HT(7) receptors are present throughout the ventral wall of the canine stomach, but the efficacy (expressed as log tau) is clearly greater close to the lesser curvature. Differences in 5-HT(7) receptor expression at least partially explain the functional differences.