Relaxatory responses of canine proximal stomach to esophageal and duodenal distension. Importance of vagal pathways

Contribution of different triggers to the gastric accommodation reflex in humans

Accommodation of the stomach consists of a vagally mediated relaxation of the proximal stomach, providing the meal with a reservoir. Our aim was to study whether, similar to other vagally mediated processes, the accommodation reflex is also determined by cephalic, oropharyngeal, gastric, and intestinal phases. Eleven healthy subjects underwent in randomized order five gastric barostat studies and two satiety drinking tests. In all studies, isobaric tone measurements (at minimal distending pressure + 2 mmHg) were performed 20 min before and 20 min after a nutrient stimulus. The stimuli included only visual and olfactory exposure to a meal (cephalic stimulation), taking liquid nutrient in the mouth without swallowing (sham feeding), ingestion of a 200-ml 300-kcal nutrient meal with blocked outflow to the pylorus (gastric retention), and meal infusion through a nasointestinal tube (duodenal instillation), or normal ingestion (control). During satiety testing, subjects ingested liquid nutrient at a fixed rate of 15 ml/min until maximum satiety, with an inflated or deflated intrapyloric balloon assembly. Progressively bigger gastric relaxatory responses were seen with cephalic stimulation (18 +/- 19 ml), sham feeding (54 +/- 21 ml), gastric retention (95 +/- 47), duodenal instillation (144 +/- 33), and control (232 +/- 33 ml). The amount of nutrient ingested at maximum satiety was significantly lower with an inflated intrapyloric balloon (1,223 +/- 103 vs. 1,392 +/- 124 ml, P < 0.05). The accommodation reflex in humans lacks a cephalic phase, but it can be activated from the oropharynx, the stomach, and the duodenum. Blocking passage to the duodenum significantly decreases the amplitude of the accommodation reflex and induces early satiety.

Factors regulating vagal sensory development: potential role in obesities of developmental origin

Contributors to increased obesity in children may include perinatal under- or overnutrition. Humans and rodents raised under these conditions develop obesity, which like obesities of other etiologies has been associated with increased meal size. Since vagal sensory innervation of the gastrointestinal (GI) tract transmits satiation signals that regulate meal size, one mechanism through which abnormal perinatal nutrition could increase meal size is by altering vagal development, possibly by causing changes in the expression of factors that control it. Therefore, we have begun to characterize development of vagal innervation of the GI tract and the expression patterns and functions of the genes involved in this process. Important events in development of mouse vagal GI innervation occurred between midgestation and the second postnatal week, suggesting they could be vulnerable to effects of abnormal nutrition pre- or postnatally. One gene investigated was brain- derived neurotrophic factor (BDNF), which regulates survival of a subpopulation of vagal sensory neurons. BDNF was expressed in some developing stomach wall tissues innervated by vagal afferents. At birth, mice deficient in BDNF exhibited a 50% reduction of putative intraganglionic laminar ending mechanoreceptor precursors, and a 50% increase in axons that had exited fiber bundles. Additionally, BDNF was required for patterning of individual axons and fiber bundles in the antrum and differentiation of intramuscular array mechanoreceptors in the forestomach. It will be important to determine whether abnormal perinatal environments alter development of vagal sensory innervation of the GI tract, involving effects on expression of BDNF, or other factors regulating vagal development.

The use of gastric electrical signals for algorithm for automatic eating detection in dogs

Food ingestion increases fundic impedance (FI) and reduces antral slow wave rate (SWR). Our aim was to determine if such changes can be integrated into an algorithm for automatic eating detection (AED). When incorporated in implantable medical devices, AED can time treatment to food intake without need for patient input. Four dogs were implanted with fundic and antral electrodes, connected to an implantable recording device. Changes in FI and SWR induced by fixed meals of different weights were determined, and were used to build an AED algorithm. Its performance was then tested on the same animals given an ad libitum access to food. The effects of gastric balloon distension and nitroglycerin on SWR and FI were also tested. Fixed meals reduced SWR in a weight-dependent manner, R(2) = 0.936, P < 0.05 baseline compared to 50, 100, 200 and 400 g. Meals increased FI above baseline in a weight-dependent manner; R(2) = 0.994, P < 0.05 baseline compared to 200 and 400 g. During ad libitum intake, the AED algorithm detected 86% of all meals > or =15 g. Gastric distension reduced SWR and increased FI. Nitroglycerin reduced SWR. AED, using changes in FI and gastric SWR is feasible. Changes in FI and SWR are induced primarily by the presence of food in the stomach.

Duodenal afferent input converges onto T9-T10 spinal neurons responding to gastric distension in rats

Clinically, the overlap of gastroduodenal symptoms, such as visceral pain or hypersensitivity, is often observed in functional gastrointestinal disorders. The underlying mechanism may be related to intraspinal neuronal processing of noxious convergent inputs from the stomach and the intestine. The purpose of this study was to examine whether single low thoracic (T9-T10) spinal neurons responded to both gastric and duodenal mechanical stimulation. Extracellular potentials of single T9-T10 spinal neurons were recorded in pentobarbital anesthetized, paralyzed, and ventilated male rats. Graded gastric distensions (GD, 20, 40, 60 mm Hg, 20 s) were induced by air inflation of a latex balloon surgically placed in the stomach. Graded duodenal distensions (DD, 0.2, 0.4, 0.6 ml, 20 s) were produced by water inflation of a latex balloon placed into the duodenum. Of 70 deeper (depth from dorsal surface of spinal cord: 0.3-1.2 mm) spinal neurons responsive to noxious GD (> or =40 mm Hg), 44(63%) also responded to noxious DD (> or =0.4 ml). Similarly, 13/17 (76%) superficial neurons (depth <0.3 mm) responded to both GD and DD. Of 57 gastroduodenal convergent neurons, 41 (72%) had excitatory and 6 had inhibitory responses to both GD and DD; the remaining neurons exhibited multiple patterns of excitation and inhibition. 43/57 (75%) gastroduodenal convergent neurons had low-threshold (< or =20 mm Hg) responses to GD, whereas 42/57 (74%) of these neurons had high-threshold (> or =0.4 ml) responses to DD. In addition, 34/40 (85%) gastroduodenal convergent neurons had somatic receptive fields on the back, flank, and medial/lateral abdominal areas. These results suggested that superficial and deeper T9-T10 spinal neurons received innocuous and/or noxious convergent inputs from mechanical stimulation of the stomach and duodenum. Gastroduodenal convergent spinal neurons might contribute to intraspinal sensory transmission for cross-organ afferent-afferent communication between the stomach and duodenum and play a role in visceral nociception and reflexes.

Total fundoplication does not obstruct the esophageal secondary peristalsis: investigation with pre- and postoperative 24-hour pH-multichannel intraluminal impedance

AIM

To determine the impact of total fundoplication on the spontaneous esophageal clearance, known as secondary peristalsis.

BACKGROUND

Although there is general agreement that total fundoplication is not an obstacle to bolus swallowing (primary peristalsis), whether it is an obstacle to spontaneous esophageal clearance (secondary peristalsis) is still not clear. Based on 24-hour monitoring, multichannel intraluminal impedance was used to calculate the time of spontaneous bolus clearance (BCT).

METHODS

Mean BCT was prospectively calculated in 15 consecutive patients before and after total fundoplication. BCT was calculated in seconds including all the gastroesophageal reflux episodes, whereas bolus swallows (solid meals and liquid swallows) were excluded from the analysis.

RESULTS

BCT was extrapolated from 1,057 episodes in the 623 h of study. Overall, BCT did not change after surgery (13.6 +/- 4 vs. 15.2 +/- 10 s; p = nonsignificant) and in the upright (12.2 +/- 3 vs. 16.5 +/- 7 s; p = nonsignificant) and recumbent position (22.9 +/- 9 vs. 23.0 +/- 9 s; p = nonsignificant).

CONCLUSIONS

In this study total fundoplication did not affect the BCT by combined 24-hour ph monitoring and multichannel intraluminal impedance.

Laparoscopic Nissen-Rossetti fundoplication with routine use of intraoperative endoscopy and manometry: technical aspects of a standardized technique

BACKGROUND

Several different ways of fashioning a total fundoplication lead to different outcomes. This article addresses the technical details of the antireflux technique we adopted without modifications for all patients with GERD beginning in 1972. In particular it aims to discuss the relation between the mechanism of function of the wrap and the physiology of the esophagus.

METHODS

The study population consisted of 380 patients affected by GERD with a 1-year minimum of follow-up who underwent laparoscopic Nissen-Rossetti fundoplication by a single surgeon.

RESULTS

No conversion to open surgery and no mortality occurred. Major complications occurred in 4 patients (1.1%). Follow-up (median 83 months; range: 1-13 years) was achieved in 96% of the patients. Ninety-two percent of the patients were satisfied with the results of the procedure and would undergo the same operation again. Postoperative dysphagia occurred in 3.5% of the patients, and recurrent heartburn was observed in 3.8%.

CONCLUSIONS

Laparoscopic Nissen-Rossetti fundoplication with the routine use of intraoperative manometry and endoscopy achieved good outcomes and long-term patient satisfaction with few complications and side-effects. Appropriate preoperative investigation and a correct surgical technique are important in securing these results.

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.

Partial gastric volumes and upper abdominal sensations in functional dyspeptic and GERD patients: a 3D ultrasonographic study

OBJECTIVES

The aim of the study was to evaluate the change in proximal and distal gastric volumes after ingestion of a nutrient drink and its relationship to upper abdominal sensations using three-dimensional ultrasonography.

METHODS

Fifty FD patients, 20 GERD patients patients and 35 healthy controls participated. Partial gastric volumes and sensations were assessed while fasting and after ingestion of a nutrient drink (500 mL, 300 kcal). Division of partial gastric volumes by total gastric volume was used to calculate proximal and distal gastric volume ratios.

RESULTS

The proximal gastric volume ratio was smaller in FD patients and larger in GERD patients compared to controls (p < 0.001 and p= 0.008, respectively). FD patients with impaired proximal relaxation (46%) had a larger increase in distal gastric volume (p= 0.008) and higher fullness sensations (p= 0.027) compared to FD patients with normal proximal relaxation. Fullness was related to distal gastric volume in both GERD patients and healthy controls (r= 0.761, p < 0.001 and r= 0.674, p= 0.001, respectively). In FD patients this relationship was not observed.

CONCLUSIONS

Impaired proximal gastric volume change after ingestion of a nutrient drink is associated with a larger distal gastric volume and increased fullness. In health and in GERD patients, the distal stomach is important in the regulation of fullness. However, in FD patients with normal or altered gastric volume distribution, this relationship is disturbed, implying that other causes are involved in the excessive generation of fullness.

A genetic approach for investigating vagal sensory roles in regulation of gastrointestinal function and food intake

Sensory innervation of the gastrointestinal (GI) tract by the vagus nerve plays important roles in regulation of GI function and feeding behavior. This innervation is composed of a large number of sensory pathways, each arising from a different population of sensory receptors. Progress in understanding the functions of these pathways has been impeded by their close association with vagal efferent, sympathetic, and enteric systems, which makes it difficult to selectively label or manipulate them. We suggest that a genetic approach may overcome these barriers. To illustrate the potential value of this strategy, as well as to gain insights into its application, investigations of CNS pathways and peripheral tissues involved in energy balance that benefited from the use of gene manipulations are reviewed. Next, our studies examining the feasibility of using mutations of developmental genes for manipulating individual vagal afferent pathways are reviewed. These experiments characterized mechanoreceptor morphology, density and distribution, and feeding patterns in four viable mutant mouse strains. In each strain a single population of vagal mechanoreceptors innervating the muscle wall of the GI tract was altered, and was associated with selective effects on feeding patterns, thus supporting the feasibility of this strategy. However, two limitations of this approach must be addressed for it to achieve its full potential. First, mutation effects in tissues outside the GI tract can contribute to changes in GI function or feeding. Additionally, knockouts of developmental genes are often lethal, preventing analysis of mature innervation and ingestive behavior. To address these issues, we propose to develop conditional gene knockouts restricted to specific GI tract tissues. Two genes of interest are brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), which are essential for vagal afferent development. Creating conditional knockouts of these genes requires knowledge of their GI tract expression during development, which little is known about. Preliminary investigation revealed that during development BDNF and NT-3 are each expressed in several GI tract regions, and that their expression patterns overlap in some tissues, but are distinct in others. Importantly, GI tissues that express BDNF or NT-3 are innervated by vagal afferents, and expression of these neurotrophins occurs during the periods of axon invasion and receptor formation, consistent with roles for BDNF or NT-3 in these processes and in receptor survival. These results provide a basis for targeting BDNF or NT-3 knockouts to specific GI tract tissues, and potentially altering vagal afferent innervation only in that tissue (e.g., smooth muscle vs. mucosa). Conditional BDNF or NT-3 knockouts that are successful in selectively altering a vagal GI afferent pathway will be valuable for developing an understanding of that pathway's roles in GI function and food intake.

Concomitant variations of gastric tone and duodenal motility in humans: results of a placebo-controlled study assessing octreotide and sumatriptan

OBJECTIVE

To describe the concomitant effects of octreotide and sumatriptan on fundic tone and duodenal phase III activity.

MATERIAL AND METHODS

A double-blind study was performed in nine volunteers, studied for 2 h after receiving 50 microg octreotide, 6 mg sumatriptan or placebo. Fundic tone variations were assessed by barostat while antroduodenal motility was studied concomitantly using manometry.

RESULTS

A rapid increase in intrabag volume was observed in all but one subject after both sumatriptan and octreotide administration, while only two subjects exhibited a volume variation after placebo, p<0.01. A significant decrease in the number of phasic contractions was observed after octreotide, while sumatriptan reduced only wave amplitudes (p<0.05). A total of 13 concomitant duodenal phase III-like activities were observed in the duodenum after octreotide, 3 after sumatriptan and 4 after placebo, all followed by spontaneous fundic relaxation with disappearance of phasic contractions, p<0.05. Spontaneous phase III activities were different from phases III-like activities after octreotide in velocity and duration (p<0.05).

CONCLUSIONS

Octreotide induced concomitant fundic relaxation, disappearance of phasic contractions and duodenal phase III-like activity. Sumatriptan relaxed the proximal stomach and reduced the amplitude of fundic phasic contractions without affecting concomitant antroduodenal phase III activity.

Effects of partial (Belsey Mark IV) and complete (Nissen) fundoplication on proximal gastric function and esophagogastric junction dynamics

OBJECTIVES

This study aimed to assess the effects of Belsey Mark IV 270 degrees (partial) and Nissen 360 degrees (complete) fundoplication on proximal stomach function, transient lower esophageal sphincter relaxation (TLESR) elicitation and the esophagogastric junction (EGJ) pressure profile during TLESR to further elucidate the mechanism of action of fundoplication.

METHODS

Ten patients after partial and 10 patients after complete fundoplication were studied. High-resolution EGJ manometry and pH recording were performed for 1 h at baseline and 2 h following meal ingestion (500 mL/300 kcal). Three dimensional (3D) ultrasonographic images of the stomach were acquired every 15 min after meal ingestion. From the 3D ultrasonographic images, proximal gastric volumes were computed.

RESULTS

Postprandial proximal to complete gastric volume distribution ratios were larger among patients after partial (0.42 +/- 0.028) compared with patients after complete fundoplication (0.37 +/- 0.035; p < 0.05). Partial fundoplication patients had a markedly greater postprandial rate of TLESR (1.7 +/- 0.3/h) than patients after complete fundoplication (0.8 +/- 0.2/h; p < 0.05). The axial EGJ pressure profile was minimally affected by partial fundoplication but instead markedly changed after complete fundoplication.

CONCLUSIONS

Patients after partial fundoplication exhibit a larger meal-induced increase in proximal stomach volume, a higher TLESR rate, and a minimally affected axial EGJ pressure profile compared to patients after complete fundoplication.

Hindbrain chemical mediators of reflex-induced inhibition of gastric tone produced by esophageal distension and intravenous nicotine

The purpose of this study was to activate a vagovagal reflex by using esophageal distension and nicotine and test whether hindbrain nitric oxide and norepinephrine are involved in this reflex function. We used double-labeling immunocytochemical methods to determine whether esophageal distension (and nicotine) activates c-Fos expression in nitrergic and noradrenergic neurons in the nucleus tractus solitarii (NTS). We also studied c-Fos expression in the dorsal motor nucleus of the vagus (DMV) neurons projecting to the periphery. Esophageal distension caused 19.7 +/- 2.3% of the noradrenergic NTS neurons located 0.60 mm rostral to the calamus scriptorius (CS) to be activated but had little effect on c-Fos in DMV neurons. Intravenous administration of nicotine caused 19.7 +/- 4.2% of the noradrenergic NTS neurons 0.90 mm rostral to CS to be activated and, as reported previously, had no effect on c-Fos expression in DMV neurons. To determine whether norepinephrine and nitric oxide were central mediators of esophageal distension-induced decrease in intragastric pressure (balloon recording), N(G)-nitro-L-arginine methyl ester microinjected into the NTS (n = 5), but not into the DMV, blocked the vagovagal reflex. Conversely, alpha2-adrenergic blockers microinjected into the DMV (n = 7), but not into the NTS, blocked the vagovagal reflex. These data, in combination with our earlier pharmacological microinjection data with nicotine, indicate that both esophageal distension and nicotine produce nitric oxide in the NTS, which then activates noradrenergic neurons that terminate on and inhibit DMV neurons.

Gastric tone variations during gastric infusion of fiber-supplemented formulas

BACKGROUND AND AIM

Despite gastric feeding being a common method of artificial nutritional support, little is known about the effects of enteral nutrition on fundic motor function. The objective of this study was to assess variations of fundic tone and their relation to antroduodenal motility before, during and after nasogastric feeding supplemented or not with fibers.

METHOD

Double-blinded studies were performed in random order with the three different diets (2100 kJ) in eight volunteers: fiber free (FF), insoluble fiber (IF) or mixed fiber (MF). Fundic tone was recorded by barostat concomitantly with antroduodenal manometry.

RESULTS

Before the infusion, seven spontaneous fundic relaxations occurred during the 24 studies. Concomitantly or less than 2 min before these relaxations, phase III of the migrating motor complex (MMC) with a duodenal onset was recorded. Only the 17 studies without spontaneous fundic relaxation (4 FF, 6 MF, 7 IF) were suitable for the assessment of fundic response to infusion. Disappearance of the volume waves at the beginning and during the whole infusion was observed in 11/17 studies (FF 50%, MF 66% and IF 71%, NS), but a proximal gastric relaxation following the beginning of the infusion occurred in only three individuals, one with the FF and two with IF. When it occurred, fundic relaxation was observed within 2 min and was not different from those observed spontaneously.

CONCLUSION

Gastric infusion of a polymeric diet, supplemented or not with fiber, did not promote fundic relaxation in most of the cases but often induced a disappearance of gastric volume waves.

Does the nutrient drink test accurately predict postprandial gastric volume in health and community dyspepsia?

Nutrient drink tests have been proposed as a surrogate for measurement of gastric accommodation. To study the relationship of maximum tolerated volume (MTV) during nutrient drink test and gastric volumes measured by single-photon emission computed tomography (SPECT) in healthy controls and functional dyspepsia (FD) patients. We reviewed data from 85 healthy controls and 35 FD residents of south-eastern Minnesota. All underwent standardized nutrient drink and SPECT studies between August 2000 and June 2003. To test for associations between nutrient drink test and SPECT gastric volumes, we used multiple linear regression and partial regression analyses, assigning age, gender, dyspepsia status and postprandial symptoms as covariates in the model. In the combined group (healthy and FD), MTV was weakly associated with fasting gastric volume (r = 0.43, P = 0.0001) and with volume response to feeding (r = 0.25, P = 0.006). In the FD group, associations were similar (fasting r = 0.53, P = 0.001; postmeal r = 0.32, P = 0.06). After accounting for covariates, MTV only explained 13 and 3% of variations in fasting and postprandial volumes measured by SPECT. MTV during the nutrient drink test does not accurately reflect gastric volume measurements by SPECT in healthy controls and a sample of people in the community with FD.

Relationship between partial gastric volumes and dyspeptic symptoms in fundoplication patients: a 3D ultrasonographic study

OBJECTIVES

Impaired gastric accommodation may induce dyspeptic symptoms in postfundoplication patients. Our aim was to assess the effect of a meal on total and partial gastric volumes in relation to dyspeptic symptoms in both dyspeptic and nondyspeptic fundoplication patients using three-dimensional (3D) ultrasonography.

METHODS

Eighteen postfundoplication patients of whom eight with and ten without dyspeptic symptoms and eighteen controls were studied. Three-dimensional ultrasonographic images of the stomach were acquired and symptoms were scored while fasting and at 5, 15, 30, 45, and 60 min after ingesting of a 500-ml liquid meal. From the 3D ultrasonographic images of the stomach the total, proximal, and distal gastric volumes were computed.

RESULTS

Dyspeptic and nondyspeptic fundoplication patients exhibited similar total gastric volumes at 5 min postprandially compared to controls, whereas smaller total gastric volumes were observed from 15 to 60 min postprandially (p = 0.007 and p < 0.001, respectively). Postprandial proximal/total gastric volume ratios were markedly reduced in both dyspeptic (0.39 +/- 0.016; p < 0.05) and nondyspeptic (0.38 +/- 0.016; p < 0.01) fundoplication patients compared to controls (0.47 +/- 0.008). In contrast, distal/total gastric volume ratios were larger in dyspeptic fundoplication patients (0.14 +/- 0.008) compared to both nondyspeptic fundoplication patients (0.11 +/- 0.007); p < 0.05) and controls (0.07 +/- 0.003); p < 0.001). Dyspeptic fundoplication patients had a higher postprandial score for fullness, nausea, and pain than nondyspeptic patients (p < 0.05) and controls (p < 0.05). Meal-induced distal gastric volume increase correlated significantly with the increase in fullness (r = 0.68; p < 0.01).

CONCLUSIONS

After a liquid meal, fundoplication patients exhibit a larger volume of the distal stomach compared with controls. Distal stomach volume was more pronounced in dyspeptic fundoplication patients and related with the increase in postprandial fullness sensations.

Increased short-term food satiation and sensitivity to cholecystokinin in neurotrophin-4 knock-in mice

Neurotrophin-4 (NT-4) knockout mice exhibited decreased innervation of the small intestine by vagal intraganglionic laminar endings (IGLEs) and reduced food satiation. Recent findings suggested this innervation was increased in NT-4 knock-in (NT-4KI) mice. Therefore, to further investigate the relationship between intestinal IGLEs and satiation, meal patterns were characterized using solid and liquid diets, and cholecystokinin (CCK) effects on 30-min solid diet intake were examined in NT-4KI and wild-type mice. NT-4KI mice consuming the solid diet exhibited reduced meal size, suggesting increased satiation. However, compensation occurred through increased meal frequency, maintaining daily food intake and body weight gain similar to controls. Mutants fed the liquid diet displayed a decrease in intake rate, again implying increased satiation, but meal duration increased, which led to an increase in meal size. This was compensated for by decreased meal frequency, resulting in similar daily food intake and weight gain as controls. Importantly, these alterations in NT-4KI mice were opposite, or different, from those of NT-4 knockout mice, further supporting the hypothesis that they are specific to vagal afferent signaling. CCK suppressed short-term intake in mutants and controls, but the mutants exhibited larger suppressions at lower doses, implying they were more sensitive to CCK. Moreover, devazepide prevented this suppression, indicating this increased sensitivity was mediated by CCK-1 receptors. These results suggest that the NT-4 gene knock-in, probably involving increased intestinal IGLE innervation, altered short-term feeding, in particular by enhancing satiation and sensitivity to CCK, whereas long-term control of daily intake and body weight was unaffected.

An impaired accommodation of the proximal stomach to a meal is associated with symptoms after distal gastrectomy

OBJECTIVE

The aim of this study was to assess gastric emptying and postprandial proximal gastric tone variations depending on the presence of postoperative symptoms after Billroth II gastrectomy (BII).

METHODS

A total of 16 consecutive patients were prospectively studied 10 +/- 3 months after distal gastrectomy for antral cancer. No evidence of cancer recurrence was detected at the time of the study. Ten patients were asymptomatic after surgery, whereas six patients were considered as symptomatic because of at least one weekly epigastric pain, postprandial fullness, nausea, or vomiting. The fasting fundus volume and tone, the onset of a gastric relaxation after a standard 200-kcal liquid meal, and the characteristics of this relaxation (delay of occurrence, amplitude) were determined with a barostat. Patient results were compared to normal values obtained in 12 healthy volunteers. Gastric emptying studies were performed in all patients using the C(13) acid octanoic breath test after a 250-kcal meal.

RESULTS

In the patients, both fasting fundus tone (BII 7.0 +/- 0.5, controls 8.4 +/- 2.4 mm Hg) and volume (BII 108 +/- 11, controls 119 +/- 29 ml) were not different from controls. Fasting fundus tone was lower in asymptomatic patients than in symptomatic patients (6.5 +/- 0.4 vs 8.1 +/- 0.5 mm Hg, p < 0.04). Gastric relaxation was observed immediately after the meal in all asymptomatic patients as well as in controls. In contrast, gastric relaxation occurred in only two of six symptomatic patients (p < 0.01); when it occurred it was delayed by the meal and was observed only 23 +/- 1 min after food intake. When a relaxation occurred, its amplitude was higher than that observed in controls both in asymptomatic and symptomatic patients (294 +/- 21 vs 179 +/- 53 ml, p < 0.02).

CONCLUSIONS

After distal gastrectomy, gastric accommodation is impaired (i.e., absent or delayed) in symptomatic patients. When relaxation exists in these patients, its amplitude is higher than in control subjects.

Effects of glucagon-like peptide-1 and feeding on gastric volumes in diabetes mellitus with cardio-vagal dysfunction

Glucagon-like peptide-1 (GLP-1) increases gastric volume in humans possibly through the vagus nerve. Gastric volume response to feeding is preserved after vagal denervation in animals. We evaluated gastric volume responses to GLP-1 and placebo in seven diabetic patients with vagal neuropathy in a crossover study. We also compared gastric volume response to feeding in diabetes with that in healthy controls. We measured gastric volume using SPECT imaging. Data are median (interquartile range). In diabetic patients, GLP-1 did not increase gastric volume during fasting [5 mL (-3; 30)] relative to placebo [4 mL (-14; 50) P = 0.5], or postprandially [Delta postprandial minus fasting volume 469 mL (383; 563) with GLP-1 and 452 mL (400; 493) with placebo P = 0.3]. Change in gastric volume over fasting in diabetic patients on placebo was comparable to that of healthy controls [452 mL (400; 493)], P = 0.5. In contrast to effects in health, GLP-1 did not increase gastric volume in diabetics with vagal neuropathy, suggesting GLP-1's effects on stomach volume are vagally mediated. Normal gastric volume response to feeding in diabetics with vagal neuropathy suggests that other mechanisms compensate for vagal denervation.

Role of 5-HT1B/D receptors in canine gastric accommodation: effect of sumatriptan and 5-HT1B/D receptor antagonists

The 5-HT1B/D receptor agonist sumatriptan has been proposed to treat dyspeptic symptoms, because it facilitates gastric accommodation. It is unknown whether stimulation of 5-HT1B/D receptors is involved. Thus, in four conscious dogs, we compared the effects of sumatriptan alone or combined with N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-[1,1-biphenyl]-4-carboxamide hydrocloride (GR-127935), N-[3-[3 (dimethylamino)-ethoxy]-4-methoxyphenyl]-2'-[methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)]-[1,1-biphenyl]-4-carboxamide hydrocloride (SB-216641 hydrochloride), or 3-[4-(4-chloro-phenyl)piperazin-1-yl]-1,1-diphenyl-2-propanol hydrochloride (BRL-15572 hydrochloride) (respectively, nonselective 5-HT1B/D, selective 5-HT1B, and selective 5-HT1D receptor antagonists) on gastric accommodation to isobaric distensions performed with a barostat. An exponential and a linear model were used to fit the pressure-volume relationship. An exponential equation fitted the data better than a linear equation. Sumatriptan (800 nmol/kg iv) induced an immediate gastric relaxation (Deltavolume: 112 +/- 44 ml, P < 0.05). After sumatriptan, the pressure-volume curve was shifted toward significantly higher volumes. This effect was fully reversed by GR-127935 or SB-216641 but not by BRL-15572. In conclusion, 5-HT1B receptors seem to play an important role in modulating gastric accommodation to a distending stimulus. An exponential model for pressure-volume curves fits well with the concept of gastric adaptive relaxation.

Involvement of glutamate in gastrointestinal vago-vagal reflexes initiated by gastrointestinal distention in the rat

Vago-vagal reflexes play an integral role in the regulation of gastrointestinal function. Although there have been a number of reports describing the effects of various stimuli on the firing rates of vagal afferent fibers and vagal motor neurons, little is known regarding the neurotransmitters that mediate the vago-vagal reflexes. In the present work, we investigated the role of glutamate in the vago-vagal reflex induced by gastrointestinal distention. Using single-cell recording techniques, we determined the effects of gastric and duodenal distention on the firing rates of gut-related neurons in the dorsal vagal complex, in the absence and presence of glutamate antagonists. Kynurenic acid, a competitive glutamate receptor antagonist, injected into the dorsal vagal complex, blocked the neuronal response of neurons in the dorsal motor nucleus of the vagus and the nucleus of the solitary tract to gastrointestinal distention. Injection of glutamate into the nucleus of the solitary tract produced inhibition of dorsal motor nucleus of the vagus neurons that were also inhibited by gastric and/or duodenal distention. Thus, the distention-induced inhibition of dorsal motor nucleus of the vagus neurons may be mediated by glutamate-induced excitation of gut-related nucleus of the solitary tract neurons. To investigate the role of the various glutamate receptor subtypes in the distention-induced events, we studied the effects of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective non-NMDA receptor antagonist, and DL-2-amino-5-phosphonopentanoic acid (DL-AP5), a selective NMDA receptor antagonist. CNQX injected into the dorsal vagal complex either blocked or attenuated the inhibitory response of the neurons in the dorsal motor nucleus of the vagus and nucleus of the solitary tract neurons to gastric and duodenal distention. In contrast, DL-AP5 had less effect, especially in the vago-vagal reflex elicited by gastric distention. The results suggest (1) distention activates vagal afferents in the gastrointestinal tract; (2) the central branches of the vagal afferents from the gut terminate in the nucleus of the solitary tract and release glutamate that mainly act on non-NMDA receptors; (3) glutamate activates the inhibitory neurons in the nucleus of the solitary tract that project to the dorsal motor nucleus of the vagus; and (4) the inhibitory neurotransmitter suppresses the activity of the dorsal motor nucleus of the vagus neurons. For the excitatory neuronal responses of the dorsal motor nucleus of the vagus neurons to gastrointestinal distention, the possible circuit is that the vagal afferents containing glutamate directly activate the receptors on the dendrites of the dorsal motor nucleus of the vagus.

Vagal motor neurons in rats respond to noxious and physiological gastrointestinal distention differentially

Low-pressure gastrointestinal distention modulates gastrointestinal function by a vago-vagal reflex. Noxious visceral distention, as seen in an obstruction of the gastrointestinal tract, causes abdominal pain, vomiting and affective changes. Using single neuron recording and intracellular injection techniques, we characterized the neuronal responses of neurons in the dorsal motor nucleus of the vagus (DMNV) to low- and high-pressure distensions of stomach and duodenum. Low-pressure gastric distention inhibited the mean activity of the DMNV neurons whereas high-pressure gastric distention excited many neurons. Of 47 DMNV neurons, low-pressure gastric distention inhibited 39, excited four, and did not affect four neurons. High-pressure gastric distention inhibited 26, excited 20, and left one unaffected. Thirteen of the 39 DMNV neurons inhibited by low-pressure distention of the stomach reversed their response to excitation during high-pressure gastric distention. Among 47 DMNV neurons, low-pressure duodenal distention inhibited 30, excited 10, and did not affect the remaining seven neurons. High-pressure distention of the duodenum inhibited 25 and excited 22 neurons. Eight DMNV neurons inhibited by low-pressure duodenal distention were excited in early response to high-pressure distention of the duodenum. High-pressure duodenal distention caused an early excitation and late inhibition in the mean activity of the DMNV neurons while low-pressure duodenal distention only produced late inhibition. These results suggest that different reflexes are present between physiological distention and noxious stimulation of gastrointestinal tract.

Effects of various diets on gastric tone in the proximal portion of the stomach of horses

OBJECTIVE

To assess gastric tone in the proximal portion of the stomach in horses during and after ingestion of 4 diets (2 diets of grain and 2 diets of hay).

ANIMALS

6 adult horses.

PROCEDURE

A polyester bag with a volume of approximately 1,600 ml was inserted through a gastric cannula into the proximal portion of the stomach of each horse. Internal pressure of the bag was maintained at 2 mm Hg by use of an electronic barostat, and changes in bag volume were recorded before, during, and after horses consumed diets of grain or hay. Each horse was fed 0.5 and 1.0 g of grain/kg and 0.5 and 1.0 g of hay/kg. Changes in bag volume measured by use of the barostat were indirectly related to changes in tone of the gastric wall.

RESULTS

Food intake caused a distinctly significant biphasic increase in volume. The first phase was during active ingestion, which was followed shortly by a second, more prolonged postprandial phase. The ingestion-related phase of the response to intake of a diet of 1 g of hay/kg was significantly greater than that for the other diets.

CONCLUSIONS AND CLINICAL RELEVANCE

ingestion of a solid meal induces a biphasic relaxation response in the proximal portion of the stomach of horses. Magnitude of the ingestion-related phase may be determined by size of the meal.

Role of tachykininergic and cholinergic pathways in modulating canine gastric tone and compliance in vivo

Acetylcholine and tachykinins act as co-transmitters along excitatory pathways at different gut levels. Since cholinergic pathways are involved in maintaining gastric tone during fasting, our aim was to study the possible role of tachykininergic pathways in modulating canine gastric tone and compliance in vivo by using selective tachykinin receptor antagonists. In four fasting, conscious dogs, we characterized the pressure-volume relationship in the proximal stomach by using a barostat. We increased the pressure of the intragastric bag by 2 mmHg increments every 3 min, starting from a baseline value of 2 up to 12 mmHg. Drug effects were investigated by studying pressure-volume relationships before and 15 min after intravenous (i.v.) administration of SR140333, SR48968, or SR142801 (respectively, NK (1)-, NK (2)-, and NK (3)-receptor antagonist, each at the dose of 1 mg kg (-1)) or atropine (100 microg kg (-1)). Pressure-volume curves were fitted by nonlinear regression analysis. Before drug administration, the curve that best fitted the pressure-volume relationship was exponential. SR140333, SR48968 and SR142801 did not affect baseline gastric tone or the gastric pressure-volume curve at any distension level. At a distending pressure of 6 mmHg, the Delta volumes obtained after administration of SR140333, SR48968 or SR142801 vs control were 65 +/- 28, 27 +/- 26, 14 +/- 20 ml, respectively. The same was true even when all three antagonists were administered together to achieve simultaneous blockade of all three tachykinin receptor subtypes. Atropine increased baseline gastric volume (Delta volume = 237 +/- 15 ml; P< 0.01) and significantly (P< 0.0001) shifted the pressure-volume curve to the left. After atropine, a linear equation best fitted the pressure-volume curve. We conclude that tachykininergic pathways are not involved in modulating canine gastric tone and compliance during fasting, whereas cholinergic pathways play a major role not only in maintaining gastric tone, but also in modulating the compliance of the proximal stomach to a distending stimulus.

Neurotrophin-4 deficient mice have a loss of vagal intraganglionic mechanoreceptors from the small intestine and a disruption of short-term satiety

Intraganglionic laminar endings (IGLEs) and intramuscular arrays (IMAs) are the two putative mechanoreceptors that the vagus nerve supplies to gastrointestinal smooth muscle. To examine whether neurotrophin-4 (NT-4)-deficient mice, which have only 45% of the normal number of nodose ganglion neurons, exhibit selective losses of these endings and potentially provide a model for assessing their functional roles, we inventoried IGLEs and IMAs in the gut wall. Vagal afferents were labeled by nodose ganglion injections of wheat germ agglutinin-horseradish peroxidase, and a standardized sampling protocol was used to map the terminals in the stomach, duodenum, and ileum. NT-4 mutants had a substantial organ-specific reduction of IGLEs; whereas the morphologies and densities of both IGLEs and IMAs in the stomach were similar to wild-type patterns, IGLEs were largely absent in the small intestine (90 and 81% losses in duodenum and ileum, respectively). Meal pattern analyses revealed that NT-4 mutants had increased meal durations with solid food and increased meal sizes with liquid food. However, daily total food intake and body weight remained normal because of compensatory changes in other meal parameters. These findings indicate that NT-4 knock-out mice have a selective vagal afferent loss and suggest that intestinal IGLEs (1) may participate in short-term satiety, probably by conveying feedback about intestinal distension or transit to the brain, (2) are not essential for long-term control of feeding and body weight, and (3) play different roles in regulation of solid and liquid diet intake.

Noninvasive measurement of gastric accommodation in patients with idiopathic nonulcer dyspepsia

OBJECTIVES

Postprandial symptoms are associated with impaired postprandial gastric accommodation. The aims of this study were to apply a noninvasive method to measure accommodation of the entire stomach in healthy subjects and in patients with idiopathic dyspeptic symptoms, and to assess the frequency of abnormal gastric accommodation and emptying of solids in these patients.

METHODS

In 20 healthy volunteers and 32 tertiary referral patients, we used i.v. 99mTc-single photon emission computed tomography (SPECT) to measure fasting and postprandial gastric volumes; we expressed the volume response to feeding ("accommodation") as the change in gastric volume and the ratio of postprandial/fasting volumes. The stomach was identified in transaxial SPECT tomographic images using a semiautomated, intensity-based extraction algorithm. Whole gastric volumes were measured using AnalyzeAVW software. Gastric emptying in patients was measured by scintigraphy. We also assessed dyspeptic symptoms and the association with normal or reduced accommodation.

RESULTS

SPECT imaging detects the postprandial change in gastric volume ("accommodation") in health and disease. Among healthy subjects (eight men, 12 women), the postprandial/fasting gastric volume ratio was 4.9+/-1.7 (mean +/- SD; fifth through 95th percentiles 3-8, median 4.6). Thirteen (41%) patients with idiopathic nonulcer dyspepsia had reduced postprandial "accommodation." Gastric emptying was fast in four (13%), normal in 25 (78%), and slow in three (9%) patients. Both tests were normal in 50% of patients. Weight loss of >10 pounds tended to be more frequently observed in those with reduced "accommodation" (62% vs 32%, p = 0.09).

CONCLUSIONS

SPECT imaging noninvasively measures fasting and postprandial gastric volumes in humans. Half the patients with idiopathic nonulcer dyspepsia had impaired gastric accommodation or emptying. Reduced gastric "accommodation" was observed in 41% of a group with idiopathic nonulcer dyspepsia. Abnormal gastric emptying is less frequent (22%).

Catecholaminergic neurons in rat dorsal motor nucleus of vagus project selectively to gastric corpus

Nitric oxide synthase-immunoreactive (NOS-IR) neurons in the rat caudal dorsal motor nucleus of the vagus (DMV) project selectively to the gastric fundus and may be involved in vagal reflexes controlling gastric distension. This study aimed to identify the gastric projections of tyrosine hydroxylase-immunoreactive (TH-IR) DMV neurons, whether such neurons colocalize NOS-IR, and if they are activated after esophageal distension. Gastric-projecting neurons were identified after injection of retrograde tracers into the muscle wall of the gastric fundus, corpus, or antrum/pylorus before removal and processing of the brain stems for TH- and NOS-IR. A significantly higher proportion of corpus- compared with fundus- and antrum/pylorus-projecting neurons were TH-IR (14% compared with 4% and 2%, respectively, P < 0.05). Colocalization of NOS- and TH-IR was never observed in gastric-projecting neurons. In rats tested for c-Fos activation after intermittent esophageal balloon distension, no colocalization with TH-IR was observed in DMV neurons. These findings suggest that TH-IR neurons in the caudal DMV project mainly to the gastric corpus, constitute a subpopulation distinct from that of nitrergic vagal neurons, and are not activated on esophageal distension.

Effect of CCK pretreatment on the CCK sensitivity of rat polymodal gastric vagal afferent in vitro

To prevent the blood-borne interference and reflex actions via neighboring organs and the central nervous system, the study was conducted in an in vitro isolated stomach-gastric vagus nerve preparation obtained from overnight-fasted, urethan-anesthetized rats. Afferent unit action potentials were recorded from the gastric branch of the vagus nerve. The left gastric artery was catheterized for intra-arterial injection. In vitro we found that 1) 55/70 gastric vagal afferents (GVAs) were polymodal, responding to CCK-8 and mechanical stimuli, 13 were mechanoreceptive, and 2 were CCK-responsive; 2) sequential or randomized intra-arterial injections of CCK-8 (0.1-200 pmol) dose-dependently increased firing rate and reached the peak rate at 100 pmol; 3) the action was suppressed by CCK-A (Devazepide) but not by CCK-B (L-365,260) receptor antagonist; 4) neither antagonist blocked the mechanosensitivity of GVA fibers. These results are consistent with corresponding in vivo well-documented findings. Histological data indicate that the layered structure of the stomach wall was preserved in vitro for 6-8 h. Based on these results, it seems reasonable to use the in vitro preparation for conducting a study that is usually difficult to be performed in vivo. For instance, because there was no blood supply in vitro, the composition of the interstitial fluid, i.e., the ambient nerve terminals, can be better controlled and influenced by intra-arterial injection of a defined solution. Here we report that acutely changing the ambient CCK level by a conditioning stimulus (a preceding intra-arterial injection of increasing doses of CCK-8) reduced the CCK sensitivity of GVA terminals to a subsequent test stimulus (a constant dose of CCK-8 intra-arterial injection).

Vagal innervation of the rat duodenum

Electrophysiologic and anterograde tract tracing studies have demonstrated that the vagus nerve innervates the duodenum. These studies, however, have provided little information regarding the finer anatomic topography within the vagal complex. In this study, the retrograde neuronal tracers WGA-HRP or DiI, applied to the duodenum, were used to characterize the vagal afferent and efferent innervation of this portion of the gastrointestinal tract. This approach labeled a substantial number of motor neurons in both the medial and lateral columns of the dorsal motor nucleus of the vagus (DMNV). Vagal motor neurons innervating the duodenum were seen across the medial-lateral extent of the DMNV and between 600 microm rostral to obex and 1600 microm caudal to obex. The three branches of the vagus nerve contained efferent fibers to the duodenum. The gastric branch of the vagus nerve was the pathway that connected the majority of DMNV neurons with the duodenum. These neurons were located in the medial and middle thirds of the DMNV. The celiac branch to the duodenum was composed of axons from the majority of lateral column neurons but also contained axons from neurons in the medial column. The hepatic branch of the vagus nerve contained only a small number of cell axons. Some neurons were located medially whereas others were in the lateral third of the duodenum. Although central terminations of vagal primary afferents from the duodenum were not found in previous tract tracing studies, we observed a large number of terminals in the subpostremal/commissural region of the nucleus of the solitary tract. Similar to the motor fibers, most afferent fibers from the duodenum were located in the gastric branch of the vagus nerve, although the hepatic and celiac branches also contained afferent neurons. These results demonstrate that the vagal innervation of the duodenum is unique, being an amalgam of what would be expected following labeling of more proximal and distal portions of the GI tract. The uniqueness of the sensory and motor innervation to the duodenum has implications for hypotheses regarding the organization of vagovagal reflexes controlling gastrointestinal function.

Erythromycin enhances early postoperative contractility of the denervated whole stomach as an esophageal substitute

OBJECTIVE

To determine whether early postoperative administration of erythromycin accelerates the spontaneous motor recovery process after elevation of the denervated whole stomach up to the neck.

SUMMARY BACKGROUND DATA

Spontaneous motor recovery after gastric denervation is a slow process that progressively takes place over years.

METHODS

Erythromycin was administered as follows: continuous intravenous (i.v.) perfusion until postoperative day 10 in ten whole stomach (WS) patients at a dose of either 1 g (n = 5) or 2 g (n = 5) per day; oral intake at a dose of 1 g/day during 1.5 to 8 months after surgery in 11 WS patients, followed in 7 of them by discontinuation of the drug during 2 to 4 weeks. Gastric motility was assessed with intraluminal perfused catheters in these 21 patients, in 23 WS patients not receiving erythromycin, and in 11 healthy volunteers. A motility index was established by dividing the sum of the areas under the curves of >9 mmHg contractions by the time of recording.

RESULTS

The motility index after IV or oral administration of erythromycin at and after surgery was significantly higher than that without erythromycin (i.v., 1 g: p = 0.0090; i.v., 2 g: p = 0.0090; oral, 1 g: p = 0.0017). It was similar to that in healthy volunteers (i.v., 1 g: p = 0.2818; oral, 1 g: p = 0.7179) and to that in WS patients with >3 years of follow-up who never received erythromycin (i.v., 1 g: p = 0.2206; oral, 1 g: p = 0.8326). The motility index after discontinuation of the drug was similar or superior to that recorded under medication in four patients who did not experience any modification of their alimentary comfort, whereas it dropped dramatically parallel to deterioration of the alimentary comfort in three patients.

CONCLUSIONS

Early postoperative contractility of the denervated whole stomach pulled up to the neck under either i.v. or oral erythromycin is similar to that recovered spontaneously beyond 3 years of follow-up. In some patients, this booster effect persists after discontinuation of the drug.

Measurement of gastric emptying during and between meal intake in free-feeding Lewis rats

A new scintigraphic measurement technique is described that allows accurate assessment of gastric emptying in between as well as during a number of successive meals. Measurements were made every minute of food intake, gastric nutrient filling, and gastric emptying over a 6 h, 40 min period in conscious, free-feeding, loosely restrained rats. Before receiving access to the food, the animals had been deprived for a period of 31 h. Over the full duration of the experiment, an average rate of gastric emptying of 2.46 +/- 0.18 (SE) kcal/h was established. During most meals, however, the gastric emptying rate was increased so that an average of 26.9 +/- 2.7% of the ingested calories was emptied while the animals were feeding, with an average emptying rate of 0.15 +/- 0.014 kcal/min or 8.88 +/- 0.84 kcal/h. This transient increase in the rate of gastric emptying was followed by a subsequent slowing of gastric emptying after meal termination; in the 10-min postmeal interval, an average emptying rate of 0.96 +/- 0.12 kcal/h was found. Despite these fluctuations during and immediately after meals, a relatively constant rate of caloric emptying is maintained over longer periods. There were no differences between the emptying rate during the first meal when the gastrointestinal tract was still empty, compared with later meals when the gastrointestinal tract had been filled with food. The emptying rate during the 10-min postmeal interval, however, was significantly reduced during later meals. The results suggest that gastric emptying is controlled by different mechanisms during and after the ingestion of food and that these mechanisms remain in effect at various degrees of gastrointestinal filling.

Esophageal distension induced gastric relaxation is mediated in part by vagal peripheral reflex mechanism in rats

The effect of short-term lower esophageal distension on intragastric pressure (IGP) and the related neural pathways involved were investigated in urethane-anesthetized rats in which enteric nervous system connections were interrupted by ligations of the pylorus and the gastroesophageal junction while keeping the gastric vagus nerve trunks intact. Under these conditions, lower esophageal distension with a bolus of 0.2 to 0.5 ml saline in 0.1 ml step increments, raised the inside esophagus balloon pressure from 1.89 +/- 0.17 to 4.21 +/- 0.13 cm H2O and reduced IGP from -0.42 +/- 0.08 to -0.77 +/- 0.12 cm H2O, respectively. Bilateral cervical vagotomy partly blocked the gastric relaxation induced by 0.5 ml esophageal distension from -0.77 +/- 0.12 to -0.34 +/- 0.02 cm H2O; in contrast, a further bilateral splanchnectomy partly rebounded the effect of 0.5 ml esophageal distension from -0.34 +/- 0.02 to -0.46 +/- 0.05 cm H2O. These results suggest that the enteric nervous system may not play a prominent role in acute esophageal distension induced-gastric relaxation. However, more than 50% of this effect is central nervous system mediated (via the long vago-vagal reflex). The other 40% can be maintained without central and enteric nervous systems involvement, probably via a proposed gastric vagal afferent-esophageal collateral reflex.

Adrenergic mechanisms in the control of gastrointestinal motility: from basic science to clinical applications

Over the years, a vast literature has accumulated on the adrenergic mechanisms controlling gut motility, blood flow, and mucosal transport. The present review is intended as a survey of key information on the relevance of adrenergic mechanisms modulating gut motility and will provide an outline of our knowledge on the distribution and functional role of adrenoceptor subtypes mediating motor responses. alpha1-Adrenoceptors are located postsynaptically on smooth muscle cells and, to a lesser extent, on intrinsic neurons; alpha2-adrenoceptors may be present both pre- and postsynaptically, with presynaptic auto- and hetero-receptors playing an important role in the modulation of neurotransmitter release; beta-adrenoceptors are found mainly on smooth muscle cells. From a clinical standpoint, adrenoceptor agonists/antagonists have been investigated as potential motility inhibiting (antidiarrheal/antispasmodic) or prokinetic agents, although at present their field of application is limited to select patient groups.

Gastric relaxation in response to a soup meal in healthy subjects. A study using a barostat in the proximal stomach

BACKGROUND

Meal-induced relaxation of the proximal stomach can be investigated by means of a barostat. Using a standard liquid meat soup that elicits symptoms and a wide antrum in patients with functional dyspepsia, we aimed at finding the best meal size and fat load for studying gastric relaxation.

METHODS

In the first trial 200 ml and 500 ml meat soup (1 g fat/200 ml) was given to six healthy individuals. In the second trial a constant volume of soup (200 ml) containing graded amounts of fat (1, 10, and 20 g/200 ml) was given to seven healthy individuals. Gastric relaxation was investigated for 1 h after consumption of the soup. A sagittal cross-sectional antral was assessed ultrasonographically every 10 min, and abdominal discomfort was scored.

RESULTS

Overall, a positive response (volume increase of 30 ml or more within 5 min after consumption of the meal) was found in 26 of 30 (87%) investigations. Individual maximal responses ranged from 38 to 482 ml (mean, 180 ml +/- 128). Area under the time-volume curve (AUC) was similar after 200 and 500 ml soup (mean, 100 ml/30 min and 107 ml/30 min, respectively). AUC increased with increasing fat content, with a significant difference between the low-fat and high-fat meal (p < 0.05). The barostat bag induced fed-state antral contractions in most individuals (p < 0.001). There was a negative correlation between AUC and postprandial abdominal discomfort (p = 0.04).

CONCLUSIONS

The barostat is a sensitive technique for detecting gastric relaxation, also in response to our standard meat soup meal. The postprandial relaxation response in healthy individuals in dependent on the fat content of the meal. The barostat bag may alter gastric motor activity. Abdominal discomfort after soup ingestion may be related to poor gastric relaxation.

Effects of duodenal distention on fasting and postprandial antropyloroduodenal motility in humans

BACKGROUND/AIMS

Mechanoreceptors in the proximal small intestine may play an important role in the regulation of gastric emptying. Balloon distention of the duodenum causes fundic relaxation. The purpose of the present study was to determine the effect of stimulation of duodenal mechanoreceptors on both fasting and postprandial antropyloroduodenal motility in humans.

METHODS

Antropyloroduodenal pressures were recorded in 12 healthy volunteers with a sleeve-sidehole assembly, incorporating two balloons 5 and 20 cm distal to the pylorus. Duplicate proximal and distal duodenal balloon distensions with 10, 20, and 30 mL of air for 2.5 minutes were performed separately and in randomized order both during fasting and after a meal.

RESULTS

During fasting, proximal and distal distention at all volumes increased the number of isolated pyloric pressure waves (P < 0.05) and basal pyloric pressure (P < 0.05), and the response to proximal distention was greater (P < 0.05). Postprandially, proximal and distal distention increased basal pyloric pressure (P < 0.05) with a greater response to proximal distention (P < 0.05), but had no effect on isolated pyloric pressure waves. Both during fasting and postprandially, there were more synchronous and less antegrade antral waves during distention (P < 0.05). The number of duodenal pressure waves increased during proximal (P < 0.05) but not distal distention.

CONCLUSIONS

Stimulation of duodenal mechanoreceptors by balloon distention has significant and region-dependent effects on antropyloroduodenal motility that vary between fasting and postprandial states.

Effect of glyceryl trinitrate on antral motility and symptoms in patients with functional dyspepsia

Nitric oxide (NO) is considered to be an important physiologic non-adrenergic, non-cholinergic vagal transmitter in the neural regulation of gastric adaptive relaxation, which accommodates the gastric fundus to ingested food. Ten consecutive patients with functional dyspepsia (FD) and erosive prepyloric changes were studied twice on separate days, once without drug administration and once after intake of one tablet of glyceryl trinitrate (GTN), 2.6 mg, 2 h before ingestion of 500 ml meat soup. Width of antral area, amplitude (maximal area reduction as fraction of relaxed area), and frequency of antral contractions were measured ultrasonographically in standardized sections. Postprandial abdominal discomfort was scored. Without GTN, postprandial antral area and symptom scores were positively correlated (r = 0.64, p = 0.05). After administration of GTN, antral area both fasting and 10 min postprandially was reduced (p = 0.02 and p = 0.01, respectively), whereas amplitude and motility index of antral contractions tended to increase (p = 0.07 and p = 0.09, respectively). Abdominal discomfort was not significantly reduced by GTN (p = 0.13). The results suggest a relationship between postprandial antral distension and discomfort. Moreover, GTN (by generation of NO) reduced abnormal antral filling in patients with FD.

Sensorial and intestinointestinal reflex pathways in the human jejunum

Using an intestinal barostat that maintains a constant pressure within an air-filled bag (12 cm long), the authors have previously shown reflex changes in intestinal tone induced by distention. The aim of this study was to investigate the sensitivity and the responsiveness to such reflexes along the jejunum. Eight healthy volunteers were studied using two barostats operating simultaneously in the proximal and the distal jejunum (located 10 cm and 52 cm caudad to the ligament of Treitz, respectively). With one barostat, standardized distentions (1 minute duration at 10-minute intervals in 4-mm Hg increments) were produced; with the other barostat, intestinal tone was measured as volumetric variations at constant pressure. Perception was scored (0-6) by a questionnaire. The proximal jejunum relaxed in response to distention of the distal jejunum (mean +/- SE, 40% + 7% delta vol; 5.1 + 0.1 perception score at the threshold for discomfort; P less than 0.05 for both). In contrast, the distal jejunum did not respond to distention of the proximal jejunum, whereas the perception scores were similar (10% +/- 5% delta vol; 5.1 +/- 0.1 perception score). Thus, the responsiveness of the proximal jejunum to intestinointestinal reflexes fades distally, whereas intestinal sensitivity to distention remains uniform.

Perception and reflex relaxation of the stomach in response to gut distention

Acute intestinal distention in dogs induces a gastric relaxatory reflex. Our aim was to investigate this reflex in humans, including its relationship to perception. In 9 fasting healthy volunteers, we performed graded balloon distentions (2.5 min duration at 10-min intervals) of either the antroduodenal junction (n = 6) or the distal duodenum (n = 6). Gastric tone was quantified as changes in the volume of air within an intragastric bag maintained at a constant pressure by an electronic barostat. Perception was scored by a graded (0-6) questionnaire. Distention of the antroduodenal junction induced dose-related gastric relaxatory responses: distention at a level producing significant perception (5.0 +/- 0.1 perception score) induced significant relaxation (203 +/- 39 ml change in intragastric volume; p less than 0.05); lower levels of distention still induced relaxation (113 +/- 30 ml change in volume; p less than 0.05) without significant perception (1.0 +/- 0.5 perception score). In the distal duodenum, distention at the threshold for discomfort (5.1 +/- 0.3 perception score) induced significantly smaller gastric relaxatory responses (42 +/- 17 ml change in volume). Distentions below the level of significant perception (1.5 +/- 0.7 perception score) failed to induce gastric responses (14 +/- 15 ml change in volume). These data indicate that both perceived and unperceived gastric relaxatory reflexes in response to distention exist in humans and that these reflexes are region dependent.