Transient lower oesophageal sphincter relaxations--a pharmacological target for gastro-oesophageal reflux disease?

Effects of electroacupuncture on stress-induced gastric dysrhythmia and mechanisms involving autonomic and central nervous systems in functional dyspepsia

Electroacupuncture (EA) is widely used as an effective method to treat stress-related disorders. However, its mechanisms remain largely unknown. The aim of this study was to investigate the effects and mechanisms of EA on gastric slow wave (GSW) dysrhythmia and c-Fos expression in the nucleus of the solitary tract (NTS) induced by stress in a rodent model of functional dyspepsia (FD). Rats in the neonatal stage were treated using intragastric iodoacetamide. Eight weeks later, the rats were implanted with electrodes in the stomach for the measurement of GSW and electrodes into accupoints ST36 for EA. Autonomic functions were assessed by spectral analysis of heart rate variability. Rats were placed for 30 min in a cylindrical plastic tube for acute restraint stress. The involvement of a central afferent pathway was assessed by measuring c-Fos-immunoreactive cells in the NTS. 1) EA normalized restraint stress-induced impairment of GSW in FD rats. 2) EA significantly increased vagal activity (P = 0.002) and improved sympathovagal balance (P = 0.004) under stress in FD rats. 3) In FD rats under restraint stress, plasma norepinephrine concentration was increased substantially (P < 0.01), which was suppressed with EA. 4) The EA group showed increased c-Fos-positive cell counts in the NTS compared with the sham EA group (P < 0.05) in FD rats. Acute restraint stress induces gastric dysrhythmia in a rodent model of FD. EA at ST36 improves GSW under stress in FD rats mediated via the central and autonomic pathways, involving the NTS and vagal efferent pathway.

The role of high resolution oesophageal manometry in occult respiratory symptoms

PURPOSE

Cough Hypersensitivity Syndrome is the urge to cough following minimal stimulation, but its mechanism and method of provocation remain unexplained. 121 patients (44 males, 77 females; age range 18-81 years) were evaluated.

PROCEDURES

High resolution manometry was performed on consecutive patients presenting with unexplained respiratory symptoms (Respiratory Group 61). Data were compared with matched controls, i.e. dyspepsia without respiratory symptoms (Dyspepsia Group 60).

MAIN FINDINGS

Results showed increased inspiratory gastro-oesophageal pressure gradient due to significantly lower intra-oesophageal pressure on inspiration (p = 0.001), and reduced oesophageal motility in the Respiratory Group.

CONCLUSIONS

Further research in respiratory conditions characterised by decreased intrathoracic pressure during inspiration is needed.

Survey of findings in patients having persistent heartburn on proton pump inhibitor therapy

In patients with refractory heartburn while on proton pump inhibitor (PPI) therapy, changing drugs or increasing treatment to a twice a day (b.i.d.) dose has become a common practice. This study aims to study patients with persistent heartburn while on PPI therapy and to determine if persistent symptom indicates the need for more aggressive or different therapy. A retrospective review of impedance-pH tracings on PPI therapy (q.d. or b.i.d.) for patients with persistent heartburn was performed. DeMeester score, impedance, and symptom sensitive index (SSI) were used as indices. Statistical analyses were performed using chi-squared test with Yates correction and paired t-test. One hundred consecutive patients, (female 50%, male 50%, mean age 54 [range 16-83] years) were studied on q.d. (n = 45) or b.i.d. PPI (n = 55). Only 20% of the patients had abnormal DeMeester score; 41% had an abnormal impedance score and 56% had abnormal SSI; 29% had all indices normal. There was no difference between patients taking q.d. versus b.i.d. PPI for abnormal DeMeester score (22 vs. 18%), impedance (38 vs. 44%) and SSI (53 vs. 58%); P = 0.80, 0.69, and 0.77, respectively. In 56 patients with positive SSI, symptoms were due to acid reflux in 8 (14%) patients, nonacid reflux in 31 (55%) patients, and combined acid and nonacid reflux in 17 (30%) patients. Patients with persistent heartburn on PPI therapy show a variety of disorders: (i) acid reflux (20%); (ii) nonacid reflux (26%); (iii) positive SSI (56%); (iv) all normal indices (29%). These studies indicate that persistent heartburn on PPI therapy is a complex problem that may not respond to simply increasing acid inhibition.

Ameliorating effects of auricular electroacupuncture on rectal distention-induced gastric dysrhythmias in rats

Gastric slow waves (GSW) are known to regulate gastric motility and are impaired with rectal distention (RD). Electroacupuncture (EA) at body acupoints, such as ST 36, has been shown to improve gastric dysrhythmias; however, little is known about the possible effects of auricular electroacupuncture (AEA) on GSW. To study effects and possible mechanisms of AEA on RD-induced gastric dysrhythmias in rats, ten male Sprague-Dawley (SD) rats implanted with gastric serosal electrodes were studied in two different experiments in fed state. Four sessions were performed in experiment 1 as follows: control (RD, no stimulation), RD+AEA, RD+EA at body points and RD+sham AEA. Two sessions were included in experiment 2 to study mechanisms of AEA: RD + atropine and RD + atropine + AEA. It was found that 1) RD significantly decreased the percentage of normal GSW from 89.8 ± 3.5% to 76.0 ± 3.3% (P<0.05); 2) AEA increased the percentage of normal GSW during RD to 94.0 ± 2.1% (P<0.05 vs. RD) via a reduction in the percentages of tachygastria and arrhythmia (P<0.05 vs. RD); 3) atropine blocked the ameliorating effect of AEA on RD-induced gastric dysrhythmias. Our results demonstrated that RD induces gastric dysrhythmias in fed state in rats. AEA improves RD-induced gastric dysrhythmias via the vagal pathway. AEA may have a therapeutic potential in treating gastric dysrhythmias.

Treatment of GORD: Three decades of progress and disappointments

The treatment of GORD has been revolutionized by the introduction, in the 1980s, of proton-pump inhibitors as the mainstay of medical therapy and by the development of laparoscopic antireflux surgery which has definitively replaced open surgery. However, despite these major advances, many unmet therapeutic needs still persist and justify novel therapeutic approaches. The aim of this historical review is to recall the main discoveries in the treatment of GORD that have occurred during the last three decades and to discuss why some initially promising drugs or techniques have not translated into clinical applications. A careful analysis of these previous disappointing experiences should help to identify high priorities and better research programmes on the management of GORD.

Novel partial 5HT3 agonist pumosetrag reduces acid reflux events in uninvestigated GERD patients after a standard refluxogenic meal: a randomized, double-blind, placebo-controlled pharmacodynamic study

BACKGROUND

Low basal lower esophageal sphincter (LES) pressure and transient LES relaxations are major causes of gastroesophageal reflux disease (GERD). Pumosetrag, a novel selective partial 5HT3 receptor agonist, showed a promising effect on reducing reflux events in health. We aimed to evaluate the effect of pumosetrag on changes in reflux episodes, lower esophageal sphincter pressure (LESP), and specific symptoms in patients with GERD receiving a refluxogenic meal.

METHODS

Patients with GERD, who developed heartburn and/or regurgitation after ingestion of a refluxogenic meal, were randomized to 1 of 3 dose levels of pumosetrag (0.2, 0.5, or 0.8 mg) or placebo. Before and after 7 days of treatment, patients underwent manometry, intraesophageal multichannel, intraluminal impedance and pH after a standard refluxogenic meal.

KEY RESULTS

A total of 223 patients with GERD [125 (56%) women, mean (SD) age = 36 (12) years] were enrolled. No overall treatment effects were detected for the total number of reflux episodes (acidic and weakly acidic) (p > 0.5); however, significant treatment effects (p < 0.05) on the number of acid reflux episodes were observed with lower values on pumosetrag 0.2 mg (10.8 ± 1.1), 0.5 mg (9.5 ± 1.1), and 0.8 mg (9.9 ± 1.1) compared with placebo (13.3 ± 1.1). Significant treatment effects (p < 0.05) were also observed for the percentage of time pH was <4, with less time for pumosetrag at 0.5 mg (10%) and 0.8 mg (10%) compared with placebo (16%).

CONCLUSIONS & INFERENCES

In GERD, the partial 5HT3 agonist pumosetrag significantly reduced the rate of acid reflux events but did not result in a significant change in LESP or symptomatic improvement over a 1-week treatment period.

The relevance of transient lower oesophageal sphincter relaxations in the pathophysiology and treatment of GORD

Gastro-oesophageal reflux disease (GORD) is associated with the passage of gastric contents into the oesophagus resulting in potential oesophageal damage and impaired quality of life. GORD is a frequently encountered problem in today's population, with 25% of people in western populations reporting such symptoms at least once a month. Proton pump inhibitors (PPI) are the drug of choice, with surgery being employed in refractory cases. Although acid suppression is often effective, some patients remain symptomatic despite maximal PPI therapy. By delving into the mechanisms of the disease, it is clear that transient lower oesophageal sphincter relaxations are a key component of its pathophysiology. Research has demonstrated various therapeutic targets for reducing the frequency of such relaxations through GABA and glutamate modulation, for instance. This review highlights such modulations and hopes to explore these mechanisms and therapeutic targets in an area that will no doubt see a change in its pharmacological management in the near future.

Observations of Acid Reflux and Motor Function in Distal Esophagus Using Simultaneous Measurements of Intra-esophageal pH and Pressure in 8 Directions With Novel Sensor Catheter - A Feasibility Study

Background/Aims

Esophagogastric junctional lesions, such as mucosal breaks with Los Angeles grade A or B reflux esophagitis, lacerations in Mallory Weiss syndrome, and short segment Barrett's esophagus, are mainly found in the right anterior wall of the distal esophagus. Asymmetrical lower esophageal sphincter pressure and resting radial asymmetrical acid reflux may be causes of this asymmetrical distribution of reflux esophagitis and short segment Barrett's esophagus. We developed a novel pH and pressure catheter to investigate the asymmetrical distributions of pH and intra-esophageal pressure in the distal esophagus.

Methods

One healthy male volunteer was enrolled in this study. Acid reflux and motor function in distal esophagus was investigated using simultaneous measurements of intra-esophageal pH and pressure in 8 directions with novel sensor catheter.

Results

Thirty-six acid and weak acid reflux events were observed, of which 22 were circumferential refluxes with pH drops in all channels and 14 were partial refluxes with pH drops in some channels. Increase in transient circumferential intraesophageal pressure was observed just after 72.7% of the circumferential reflux and 42.9% of the partial reflux events.

Conclusions

Using a novel sensor catheter, 2 different types of acid reflux events were identified in the present study.

Ingestion of a carbonated beverage decreases lower esophageal sphincter pressure and increases frequency of transient lower esophageal sphincter relaxation in normal subjects

Transient lower esophageal sphincter relaxation (tLESR) and decreased basal lower esophageal sphincter (LES) pressure are postulated mechanisms of gastroesophageal reflux (GER). There is conflicting evidence on the effect of carbonated drinks on lower esophageal sphincter function. This study was conducted to assess the effect of a carbonated beverage on tLESR and LES pressure. High resolution manometry tracings (16 channel water-perfused, Trace 1.2, Hebbard, Australia) were obtained in 18 healthy volunteers (6 men) for 30 min each at baseline, and after 200 mL of chilled potable water and 200 mL of chilled carbonated cola drink (Pepsi [Pepsico India Ltd]). The sequence of administration of the drinks was determined by random number method generated by a computer. The analysis of tracings was done using TRACE 1.2 software by a physician who was unaware of the sequence of administration of fluids. The mean (SD) age of the participant was 37.3 (12.9) years. The median (range) frequency of tLESr was higher after the carbonated beverage (10.5 [0-26]) as compared to baseline (0 [0-3], p = 0.005) as well as after water (1 [0-14], p = 0.010). The LES pressure decreased after ingestion of the carbonated beverage (18.5 [11-37] mmHg) compared to baseline (40.5 [25-66] mmHg, p = 0.0001) and after water (34 [15-67] mmHg, p = 0.003). Gastric pressure was not different in the three groups. Ingestion of a carbonated beverage increases tLESr and lowers LES pressure in healthy subjects.

The effects of a novel metabotropic glutamate receptor 5 antagonist (AZD2066) on transient lower oesophageal sphincter relaxations and reflux episodes in healthy volunteers

BACKGROUND

Selective metabotropic glutamate receptor 5 (mGluR5) antagonists inhibit transient lower oesophageal sphincter relaxations (TLESRs) in animals and acid reflux in humans.

AIM

To assess the effect of single doses of the mGluR5 antagonist AZD2066 on TLESRs and reflux in humans.

METHODS

Healthy male volunteers received AZD2066 13 mg and placebo (part A), or AZD2066 2 mg and AZD2066 6 mg and placebo (part B), in a randomised crossover study. Postprandial manometry/pH-impedance measurements were taken after each dose.

RESULTS

A total of 13 individuals completed part A of the study and 19 individuals completed part B. There was a significant reduction in the geometric mean number of TLESRs (27%; P = 0.02) and the geometric mean number of reflux episodes (51%; P = 0.01) in subjects receiving AZD2066 13 mg compared with placebo. Adverse events in participants receiving AZD2066 13 mg were mostly related to the nervous system [dizziness (3/13); disturbance in attention (3/13)]. Adverse events were reversible and of mild intensity. There were no serious adverse events. The effects of AZD2066 appeared dose-dependent, with smaller reductions in TLESRs and reflux episodes (relative to placebo) and fewer adverse events observed for AZD2066 2 mg and AZD2066 6 mg compared with AZD2066 13 mg.

CONCLUSION

The mGluR5-mediated inhibition of TLESRs may be a useful approach for inhibiting gastro-oesophageal reflux.

Mechanisms of reflux perception in gastroesophageal reflux disease: a review

Patients with reflux symptoms often do not have excessive esophageal acid exposure, and patients with severe gastroesophageal reflux often do not have reflux symptoms. Understanding why different types of reflux induce symptoms in different patients is vital for addressing therapeutic gaps in the treatment of gastroesophageal reflux disease (GERD). Here we review studies providing insight into how gastroesophageal reflux is perceived, with a focus on comparing reflux characteristics and esophageal sensitivity among subgroups of patients with GERD. The available studies indicate that patients with nonerosive reflux disease have fewer acid reflux episodes and thus less esophageal acid exposure than patients with reflux esophagitis but perceive less intense stimuli because of greater esophageal sensitivity. Reflux characteristics other than acidity, such as the presence of bile, pepsin, liquid, or gas in reflux, and the proximal extent or volume of reflux, may also contribute to symptom perception. Factors contributing to greater esophageal sensitivity may include impaired mucosal barrier function, peripherally mediated esophageal sensitivity (enhanced esophageal receptor signaling), and centrally mediated esophageal sensitivity (physiological stressors, sensitization of spinal sensory neurons). Further insight into mechanisms of reflux perception may require a shift toward studies aimed at understanding predisposing cellular, molecular, and genetic factors.

Objective definition and detection of transient lower esophageal sphincter relaxation revisited: is there room for improvement?

BACKGROUND

The advent of drugs that inhibit transient lower esophageal sphincter relaxation (TLESR) necessitates accurate identification and scoring. We assessed the intra- and inter-assessor variability of the existing objective criteria for TLESR, improving them where necessary.

METHODS

Two 3-h postprandial esophageal manometric and pH recordings were performed in 20 healthy volunteers. Each recording was duplicated. The recordings were analyzed by five experienced observers for TLESRs based on their expert opinion. TLESRs were also analyzed for the presence of the original four criteria as well as inhibition of the crural diaphragm (ID), a prominent after-contraction (AC), acid reflux and an esophageal common cavity.

KEY RESULTS

The overall inter- and intra-observer agreements for TLESRs scored, according to observer's expert opinion, were 59% (range 56-67%) and 74% (60-89%), respectively. When TLESRs were restricted to those fulfilling the original criteria, these agreements fell to 46% (40-53%) and 60% (44-67%), respectively. Cleaning the recordings by removal of technically flawed sections improved agreements by 5%. Inclusion of additional criteria (ID and AC) resulted in inter- and intra-observer agreements of 62% (52-70%) and 69% (53-79%), respectively. A consensus analysis performed collectively by three observers and based on the new criteria (original ± ID and AC) resulted in 84% agreement between the paired recordings.

CONCLUSIONS & INFERENCES

The original criteria for the definition of TLESRs allows for substantial inter- and intra-observer variability, which can be reduced by incorporation of additional objective criteria. However, the highest level of intra-observer agreement can be achieved by consensus analysis.

In vitro effect of pantoprazole on lower esophageal sphincter tone in rats

AIM: To investigate the in vitro effects of pantoprazole on rat lower esophageal sphincter (LES) tone.

METHODS: Rats weighing 250-300 g, provided by the Yeditepe University Experimental Research Center (YÜDETAM), were used throughout the study. They were anesthetized before decapitation. LES tissues whose mucosal lining were removed were placed in a standard 30-mL organ bath with a modified Krebs solution and continuously aerated with 95% oxygen-5% carbon dioxide gas mixture and kept at room temperature. The tissues were allowed to stabilize for 60 min. Subsequently, the contractile response to 10^-6 mol/L carbachol was obtained. Different concentrations of freshly prepared pantoprazole were added directly to the tissue bath to generate cumulative concentrations of 5 × 10^-6 mol/L, 5 × 10^-5 mol/L, and 1.5 × 10^-4 mol/L. Activities were recorded on an online computer via a 4-channel transducer data acquisition system using the software BSL PRO v 3.7, which also analyzed the data.

RESULTS: Pantoprazole at 5 × 10^-6 mol/L caused a small, but statistically insignificant, relaxation in the carbachol-contracted LES (2.23% vs 3.95%). The 5 × 10^-5 mol/L concentration, however, caused a significant relaxation of 10.47% compared with the control. 1.5 × 10^-4 mol/L concentration of pantoprazol caused a 19.89% relaxation in the carbachol contracted LES (P < 0.001).

CONCLUSION: This is the first study to demonstrate that pantoprazole has a relaxing effect in isolated LESs. These results might have significant clinical implications for the subset of patients using proton pump inhibitors who do not receive full symptomatic alleviation from gastroesophageal reflux disease.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Proton pump inhibitors omeprazole, lansoprazole and pantoprazole induce relaxation in the rat lower oesophageal sphincter

Objectives

We aimed to investigate effects of the proton pump inhibitors (PPIs) omeprazole, lansoprazole and pantoprazole, which are currently used for the treatment of hyperacidity and gastro-oesophageal reflux, on the reactivity of the isolated rat lower oesophageal sphincter.

Methods

Omeprazole, lansoprazole and pantoprazole (all 10–9–10–3m, cumulatively) were tested on carbachol-induced (10–6m) contraction. In addition, the effects of PPI preincubation (all 10–3m) on the contractions induced by cumulative carbachol (10−9–10−5m), angiotensin-2 (10−9–10–5m) or electrical field stimulation (EFS; 40 V, 32 Hz, 1 ms, 10 s) were assessed. Finally, the effects of PPI on the spontaneous contractile activity of the tissue were also evaluated.

Key findings

PPI relaxed precontracted lower oesophageal sphincter in a concentration-dependent manner and suppressed carbachol-, angiotensin- and EFS-induced contractions. Furthermore, PPI attenuated spontaneous contractile activity of the tissue.

Conclusions

Omeprazole, lansoprazole and pantoprazole had a suppressor effect on lower oesophageal sphincter contractions.

Distal esophageal hypercontractility is related to abnormal acid exposure

BACKGROUND AND AIMS

Nutcracker esophagus (NE) is a frequent primary motility disorder of the distal esophagus, and the relationship with acid exposure remains controversial. We studied simultaneous distal esophageal hypercontractility (EH) using two sensors at 8 and 3 cm above the lower sphincter (LES) and abnormal exposure to acid (pH DeMeester score).

METHODS

From 400 screened patients with chest pain and heartburn, 54 (age 44.5 ± 8.8 years and 74% females) had abnormal manometry and underwent acid exposure measurement. Frequencies of the EH disorder were classic NE (EH(3 cm)) found in 29 (40.8%) patients, diffuse (EH(3,8 cm)) in 30 patients (42.3%), and upper segmental (EH(8 cm)) in 12 patients (16.9%).

RESULTS

We found a positive correlation among age with high amplitude in EH(3 cm) and EH(3,8 cm). DeMeester's score (DMS) had the lowest value for EH(3,8 cm) (2.58 ± 0.23) compared with EH(8 cm) (3.78 ± 0.3, p <0.003) and EH(3 cm) (3.12 ± 0.2, p <0.06). Surface response for joint effect of age and DMS on amplitude at EH(3 cm) confirmed the highest amplitude was for older age and lower DMS.

CONCLUSIONS

EH(3 cm) and EH(3,8 cm) were common for esophageal motility and were inversely associated with DMS. Meanwhile, acid exposure was higher in younger patients and hypercontractility was more frequent in older subjects. The former group may benefit more from proton pump inhibitors and the latter from visceral analgesics or possibly both.

Alterations confined to the gastro-oesophageal junction: the relationship between low LOSP, TLOSRs, hiatus hernia and acid pocket

The gastro-oesophageal junction is a specialised segment of the gut designed to prevent reflux of gastric contents into the oesophagus. This task is fulfilled by two structures, i.e. the lower oesophageal sphincter and the crural diaphragm, which generate a high pressure zone. Especially during low pressure at the junction, as in case of long-lasting transient lower oesophageal sphincter relaxations, reflux can occur but mainly if a positive pressure gradient exists between stomach and the oesphagogastric junction. Although patients with gastro-oesophageal reflux disease have increased oesophageal acid exposure compared to controls, the number of transient relaxations is not increased compared to healthy controls. Instead, the risk to have acid reflux is at least doubled in patients, especially in those with a hiatal hernia, most likely as a result of the supradiaphragmatic position of the acid pocket. In hiatal hernia patients, the acid pocket is indeed often trapped in the hernia above the diaphragm. Which factors exactly determine the physical composition (liquid or gas) and the proximal extent of the refluxate however requires further research.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Effects of lesogaberan on reflux and lower esophageal sphincter function in patients with gastroesophageal reflux disease

BACKGROUND & AIMS

Transient lower esophageal sphincter relaxations (TLESRs) are a major mechanism behind reflux. This study assessed the effects of lesogaberan (AZD3355), a novel gamma-aminobutyric acid type B receptor agonist, on reflux and lower esophageal sphincter (LES) function when used as add-on treatment in patients with reflux symptoms despite proton pump inhibitor (PPI) treatment.

METHODS

In this randomized, double-blind, placebo-controlled, crossover study, patients received lesogaberan (65 mg) or placebo twice on day 1 (morning/evening) and once on day 2 (morning), in addition to existing PPI treatment. Patients consumed a standardized meal 45-60 minutes after morning doses. Ambulatory impedance-pH monitoring was conducted for 24 hours after the first dose on day 1. Stationary manometry and impedance-pH monitoring was conducted for 4 hours after the third dose on day 2.

RESULTS

Of 27 randomized patients, 21 were included in the per-protocol efficacy analysis. During the 24 hours after treatment start, lesogaberan reduced the mean number of reflux events by approximately 35% compared with placebo. During the 3 postprandial hours on day 2, lesogaberan reduced the geometric mean number of TLESRs by 25% and increased geometric mean LES pressure by 28% compared with placebo. The most common adverse events were headache (placebo: 11/27 patients; lesogaberan: 8/25 patients) and paresthesia (transient; placebo: 3/27 patients; lesogaberan: 5/25 patients).

CONCLUSIONS

In patients with reflux symptoms despite PPI treatment, lesogaberan decreased the number of TLESRs and reflux episodes, and increased LES pressure compared with placebo. These findings support further evaluation of lesogaberan as an add-on treatment in patients partially responding to PPIs.

Effect of lesogaberan, a novel GABA(B)-receptor agonist, on transient lower oesophageal sphincter relaxations in male subjects

BACKGROUND

Transient lower oesophageal sphincter relaxations (TLESRs) are a major mechanism behind gastro-oesophageal reflux disease (GERD).

AIM

To assess the effect of lesogaberan (AZD3355) - a novel peripherally active GABA(B) receptor agonist - on TLESRs.

METHODS

Twenty-four healthy men were enrolled in this single-blind, placebo-controlled, randomized, single-centre, three-period crossover phase 1 study. Subjects were randomized to receive single oral doses of lesogaberan (0.8 mg/kg), baclofen (40 mg) and placebo, separated by washout periods of < or = 7 days. Subjects finished a meal 1 h after the dose. Oesophageal manometry and pH-metry measurements were taken during the 3 h after the meal.

RESULTS

Twenty-one subjects completed the study. Compared with placebo, lesogaberan 0.8 mg/kg significantly reduced the number of TLESRs by 36% [geometric mean ratio (GMR): 0.64; 95% confidence interval (CI): 0.51-0.82] and significantly reduced the number of acid reflux episodes (mean reduction: 1.6; 95% CI: 0.34-2.9). Lesogaberan also significantly increased lower oesophageal sphincter (LES) pressure by 39% compared with placebo (GMR: 1.39; 95% CI: 1.18-1.64). Comparable results were observed with baclofen. Similar numbers of adverse events were reported by subjects taking lesogaberan and placebo.

CONCLUSION

Compared with placebo, lesogaberan significantly reduced TLESRs and acid reflux episodes and increased LES pressure.

Sensory and motor innervation of the crural diaphragm by the vagus nerves

BACKGROUND & AIMS

During gastroesophageal reflux, transient lower esophageal sphincter relaxation and crural diaphragm (CD) inhibition occur concomitantly. Modifying vagus nerve control of transient lower esophageal sphincter relaxation is a major focus of development of therapeutics for gastroesophageal reflux disease, but neural mechanisms that coordinate the CD are poorly understood.

METHODS

Nerve tracing and immunolabeling were used to assess innervation of the diaphragm and lower esophageal sphincter in ferrets. Mechanosensory responses of vagal afferents in the CD and electromyography responses of the CD were recorded in novel in vitro preparations and in vivo.

RESULTS

Retrograde tracing revealed a unique population of vagal CD sensory neurons in nodose ganglia and CD motor neurons in brainstem vagal nuclei. Anterograde tracing revealed specialized vagal endings in the CD and phrenoesophageal ligament-sites of vagal afferent mechanosensitivity recorded in vitro. Spontaneous electromyography activity persisted in the CD following bilateral phrenicotomy in vivo, while vagus nerve stimulation evoked electromyography responses in the CD in vitro and in vivo.

CONCLUSIONS

We conclude that vagal sensory and motor neurons functionally innervate the CD and phrenoesophageal ligament. CD vagal afferents show mechanosensitivity to distortion of the gastroesophageal junction, while vagal motor neurons innervate both CD and distal esophagus and may represent a common substrate for motor control of the reflux barrier.

Effects of brain stem cholecystokinin-8s on gastric tone and esophageal-gastric reflex

The actions of cholecystokinin (CCK) on gastrointestinal functions occur mainly via paracrine effects on peripheral sensory vagal fibers, which engage vago-vagal brain stem circuits to convey effector responses back to the gastrointestinal tract. Recent evidence suggests, however, that CCK also affects brain stem structures directly. Many electrophysiological studies, including our own, have shown that brain stem vagal circuits are excited by sulfated CCK (CCK-8s) directly, and we have further demonstrated that CCK-8s induces a remarkable degree of plasticity in GABAergic brain stem synapses. In the present study, we used fasted, anesthetized Sprague-Dawley rats to investigate the effects of brain stem administration of CCK-8s on gastric tone before and after activation of the esophageal-gastric reflex. CCK-8s microinjected in the dorsal vagal complex (DVC) or applied on the floor of the fourth ventricle induced an immediate and transient decrease in gastric tone. Upon recovery of gastric tone to baseline values, the gastric relaxation induced by esophageal distension was attenuated or even reversed. The effects of CCK-8s were antagonized by vagotomy or fourth ventricular, but not intravenous, administration of the CCK-A antagonist lorglumide, suggesting a central, not peripheral, site of action. The gastric relaxation induced by DVC microinjection of CCK-8s was unaffected by pretreatment with systemic bethanecol but was completely blocked by NG-nitro-L-arginine methyl ester, suggesting a nitrergic mechanism of action. These data suggest that 1) brain stem application of CCK-8s induces a vagally mediated gastric relaxation; 2) the CCK-8s-induced gastric relaxation is mediated via activation of nonadrenergic, noncholinergic pathways; and 3) CCK-8s reverses the esophageal-gastric reflex transiently.

Effect of delta9-tetrahydrocannabinol, a cannabinoid receptor agonist, on the triggering of transient lower oesophageal sphincter relaxations in dogs and humans

BACKGROUND AND PURPOSE

Transient lower oesophageal sphincter relaxations (TLESRs) are the main mechanism underlying gastro-oesophageal reflux and are a potential pharmacological treatment target. We evaluated the effect of the CB(1)/CB(2) receptor agonist delta(9)-tetrahydrocannabinol (delta(9)-THC) on TLESRs in dogs. Based on these findings, the effect of delta(9)-THC was studied in healthy volunteers.

EXPERIMENTAL APPROACH

In dogs, manometry was used to evaluate the effect of delta(9)-THC in the presence and absence of the CB(1) receptor antagonist SR141716A on TLESRs induced by gastric distension. Secondly, the effect of 10 and 20 mg delta(9)-THC was studied in 18 healthy volunteers in a placebo-controlled study. Manometry was performed before and for 3 h after meal ingestion on three occasions.

KEY RESULTS

In dogs, delta(9)-THC dose-dependently inhibited TLESRs and reduced acid reflux rate. SR141716A significantly reversed the effects of delta(9)-THC on TLESRs. Similarly, in healthy volunteers, delta(9)-THC significantly reduced the number of TLESRs and caused a non-significant reduction of acid reflux episodes in the first postprandial hour. In addition, lower oesophageal sphincter pressure and swallowing were significantly reduced by delta(9)-THC. After intake of 20 mg, half of the subjects experienced nausea and vomiting leading to premature termination of the study. Other side-effects were hypotension, tachycardia and central effects.

CONCLUSIONS AND IMPLICATIONS

Delta(9)-THC significantly inhibited the increase in meal-induced TLESRs and reduced spontaneous swallowing in both dogs and humans. In humans, delta(9)-THC significantly reduced basal lower oesophageal sphincter pressure. These findings confirm previous observations in dogs and indicate that cannabinoid receptors are also involved in the triggering of TLESRs in humans.

Pathogenesis of gastro-oesophageal reflux disease and novel options for its therapy

Better understanding of the mechanisms that lead to reflux disease is an important area for future research, given the very high prevalence of this problem. During the lifetime of this journal, much has been learnt about the pathophysiology of reflux disease. Abnormally, frequent acid reflux plays a key role in pathogenesis: this reflux occurs predominantly during transient lower oesophageal sphincter relaxations. Analysis of the literature suggests that the importance of transient relaxations as the major permissive event for occurrence of acid reflux is currently substantially underestimated. 'Transient relaxation' is an inexact descriptor, as this motor programme includes inhibition of the diaphragmatic hiatus and distal oesophageal body circular muscle and contraction of the oesophageal longitudinal muscle. Laxity of the diaphragmatic hiatus and hiatus hernia are probably important factors that increase the probability for acid reflux to occur during transient relaxations and in allowing strain-induced reflux episodes. The importance of straining and low basal tone of the lower oesophageal sphincter in causing abnormal reflux has probably been overestimated, but these need more investigation. High resolution manometry is the key method for acquisition of important new insights into the normal and disordered mechanics of the antireflux function of the gastro-oesophageal junction, but as yet, the potential of this technique has been tapped relatively little. In the future, improved understanding of the mechanics of the gastro-oesophageal junction should lead to improved physical antireflux procedures. Much progress has been made in defining the control of transient relaxations and this has been translated into several promising options for a new class of drug that treats reflux disease by inhibition of transient relaxations. Clinical trials on these agents appear imminent.

A novel partial 5HT3 agonist DDP733 after a standard refluxogenic meal reduces reflux events: a randomized, double-blind, placebo-controlled pharmacodynamic study

BACKGROUND

DDP733, a selective partial 5HT(3) receptor agonist, increases lower oesophageal sphincter pressure in experimental animal models. However, its effect on gastro-oesophageal reflux or lower oesophageal sphincter pressure in humans remains unknown.

AIM

To evaluate the effect of DDP733 on reflux episodes in healthy volunteers receiving a refluxogenic meal.

METHODS

A randomized, double-blind, placebo-controlled cross-over study evaluated the pharmacodynamic effects of DDP733 (0.5, 0.8 and 1.4 mg). Healthy subjects underwent oesophageal manometry and intra-oesophageal multichannel intraluminal impedance and pH after a refluxogenic meal.

RESULTS

DDP733 0.5 mg significantly (P = 0.013) reduced the rate of reflux episodes after a refluxogenic meal from 10 (+/-2.2) on placebo to 6 (+/-1.2) on drug over a 2-h period. DDP733 0.8 and 1.4 mg had no significant effect on reducing the number of reflux episodes. Significant differences in resting lower oesophageal sphincter pressure and the proportion of time pH was <4 (placebo minus drug) after a refluxogenic meal were not observed. No serious adverse events were reported.

CONCLUSION

In healthy subjects, the partial 5HT(3) agonist DDP733 at a dose of 0.5 mg significantly reduces the rate of reflux events, but did not result in a significant change in lower oesophageal sphincter pressure at 1 h postdosing.

Review article: the pathophysiology of gastro-oesophageal reflux disease

BACKGROUND

Gastro-oesophageal reflux disease (GERD) is a common condition that develops when the reflux of stomach contents causes troublesome symptoms and/or complications.

AIM

To review the current knowledge on the underlying factors contributing to GERD, with particular emphasis on the most recent research.

METHODS

Literature searches were conducted in Medline and EMBASE. The abstracts from recent large congresses were also reviewed to ensure coverage of the latest findings.

RESULTS

The pathophysiological factors causing GERD can be split into those inducing greater exposure of the oesophagus to stomach contents, and those that provide increased perception of reflux or increased mucosal damage. Transient lower oesophageal sphincter relaxations, which are likely to be triggered by gastric distension, appear to be a key physiological cause of GERD. Excessive reflux may also be provoked by impaired oesophageal or gastric clearance mechanisms. Pre-epithelial, epithelial and post-epithelial defences all normally protect the oesophagus from injury, and may be compromised in individuals with GERD. Heartburn could also be caused by oesophageal hypersensitivity as a result of visceral neural pathway dysfunction.

CONCLUSION

The pathophysiology of GERD is multifactorial, and abnormalities in the gastro-oesophageal junction, the stomach, the oesophagus and the nervous system may all contribute to this disease state.

Modulation of upper and lower esophageal sphincter tone during sleep

BACKGROUND AND PURPOSE

The pressures generated within the upper esophageal sphincter (P(UES)) and lower esophageal sphincter (P(LES)) reflect the integrity of these barriers to gastroesophageal and pharyngoesophageal reflux, respectively. This study sought to describe the effects of sleep, respiration and posture on the function of the UES and the LES and the pressure differentials developed across them.

METHODS

Ten healthy volunteers (7M, 3F: 38+/-10 yr) without a history of sleep-disordered breathing or reflux underwent overnight polysomnography with simultaneous measurement of P(LES) and P(UES) using a purpose-built sleeve device (Dentsleeve). Posture was recorded but not controlled.

RESULTS

Subjects slept for 4.3+/-1.6h. Compared to waking values, both end-inspiratory and end-expiratory Pues were significantly less during slow wave sleep (SWS) (p<0.05). However, P(LES) was unaffected by sleep stage. During wakefulness and all stages of sleep, both P(UES) and P(LES) were greater at end-inspiration than end-expiration (p<0.05). Similar relationships were observed whether subjects were supine or in the lateral decubitus position.

CONCLUSION

Sleep decreases the effectiveness of the UES to act as a barrier to pharyngoesophageal reflux, particularly during slow wave sleep (SWS). UES pressure varies with respiration, with minimal values observed during expiration. Hence, barrier function of the UES appears most impaired during SWS, in the expiratory phase of the respiratory cycle. The LES pressure and its barrier pressure also vary with respiration, being least during expiration. However, unlike the UES, the function of the LES was unaffected by sleep.

Pharmaceutical and analytical characterisation of (2R)-(3-amino-2-fluoropropyl)sulphinic acid, a GABAB receptor agonist

(2R)-(3-amino-2-fluoropropyl)sulphinic acid (AFPSiA) is a potent GABAB agonist, which makes it a possible alternative in future GERD treatment. The degradation of AFPSiA was investigated to support the drug-development effort. The compound is too polar to be compatible with regular reversed-phase LC. Moreover, the compound and the degradation products cannot be detected by UV due to low absorption. Instead, the degradation of AFPSiA was followed by two different capillary electrophoresis methods with indirect UV detection and 1H NMR and 19F NMR. AFPSiA was very unstable in basic conditions and at temperatures above room temperature. The corresponding sulphonic acid and allylamine are formed via two separate degradation routes. Both these degradation products may cause unwanted side-effects in vivo. Aqueous solutions of AFPSiA were found to be more stable at pH between 1 and 3. It was suggested that AFPSiA should be stored frozen, preferably at -70 degrees C. In solid state, the compound can be stored at ambient conditions in closed vials with low relative humidity. A solid oral dosage form should be kept in a blister package.

Circadian change of cardiac autonomic function in correlation with intra-esophageal pH

BACKGROUND AND AIM

Although autonomic alterations are observed in patients with gastroesophageal reflux disease (GERD), the influence of visceral receptor responses on the dynamics of autonomic function remains unknown. The aim of this study was to investigate the autonomic functional changes in association with intra-esophageal pH under ambulation.

METHODS

Thirty patients referred for 48 h ambulatory pH monitoring underwent simultaneous 24 h cardiac monitoring for heart rate variability (HRV). We used linear mixed-effects models to estimate the relationship between esophageal acid exposure and power spectral analysis of HRV, including low-frequency power (0.04 < LF < 0.15 Hz), high-frequency power (0.15 < or = HF < 0.4 Hz), and LF/HF power ratio.

RESULTS

Over the 24-h period, patients with pathological reflux had lower average LF and HF powers than patients with functional heartburn, but the LF/HF power ratios were similar for the two patient groups. As we stratified the data according to waking and sleeping times, a significantly higher HF power but lower LF/HF power ratio was found during sleeping time regardless of diagnosis. In the regression analysis, esophageal pH was positively associated with change (not basal tone) of both LF and HF powers during waking, but only with change of HF power during sleeping time. The significant associations between pH values and changes in HRV decreased gradually with time. The LF/HF power ratio did not alter significantly with pH.

CONCLUSION

Esophageal acid exposure is generally associated with decreases in autonomic tone. A predominant parasympathetic fluctuation during sleeping and a superimposed sympathetic interaction during waking dictate diurnal characteristics of autonomic regulation.

Feline lower esophageal sphincter sling and circular muscles have different functional inhibitory neuronal responses

The lower esophageal sphincter (LES) has a circular muscle component exhibiting spontaneous tone that is relaxed by nitric oxide (NO) and a low-tone sling muscle that contracts vigorously to cholinergic stimulation but with little or no evidence of NO responsiveness. This study dissected the responses of the sling muscle to nitrergic innervation in relationship to its cholinergic innervation and circular muscle responses. Motor responses were induced by electrical field stimulation (EFS; 1-30 Hz) of muscle strips from sling and circular regions of the feline LES in the presence of cholinergic receptor inhibition (atropine) or NO synthase inhibition [NG-nitro-L-arginine (L-NNA)+/-atropine]. This study showed the following. First, sling muscle developed less intrinsic resting tone compared with circular muscle. Second, with EFS, sling muscle contracted (most at <or=10 Hz), whereas circular muscle relaxed >50% by 5 Hz. Third, on neural blockade with atropine or L-NNA+/-atropine, 1) sling muscle, although predominantly influenced by excitatory cholinergic stimulation, had a small neural NO-mediated inhibition, with no significant non-NO-mediated inhibition and 2) circular muscle, although little affected by cholinergic influence, underwent relaxation predominantly by neural release of NO and some non-NO inhibitory influence (at higher EFS frequency). Fourth, the sling, precontracted with bethanecol, could relax with NO and some non-NO inhibition. Finally, the tension range of both muscles is similar. In conclusion, sling muscle has limited NO-mediated inhibition to potentially augment or replace sling relaxation effected by switching off its cholinergic excitation. Differences within the LES sling and circular muscles could provide new directions for therapy of LES disorders.

Effects of (2R)-(3-amino-2-fluoropropyl)sulphinic acid (AFPSiA) on transient lower oesophageal sphincter relaxation in dogs and mechanism of hypothermic effects in mice

The effects of the novel GABA analogue (2R)-(3-amino-2-fluoropropyl)sulphinic acid (AFPSiA) on transient lower oesophageal sphincter relaxations (TLOSRs) were studied in the dog. In addition, the GABA(A)/GABA(B) selectivity was determined in vitro and in vivo, and the pharmacokinetics and the metabolism of the compound were studied in the dog and rat. TLOSRs were reduced by 55 +/- 8% after intragastric administration of AFPSiA at 14 mumol kg(-1) and did not decrease further at higher doses. When evaluated 2 and 4 h after administration, the effect declined to 37 +/- 6 and 16 +/- 9%, respectively. Spontaneous swallowing was only significantly inhibited at 100 micromol kg(-1). The oral availability of AFPSiA was 52 +/- 17 and 71 +/- 4% in the dog and rat, respectively. A fraction of AFPSiA was oxidised to the corresponding sulphonate, (2R)-(3-amino-2-fluoropropyl)sulphonic acid (AFPSoA) after oral administration to the rat and dog. In rat brain membranes, AFPSiA was found to have ten times higher affinity for rat brain GABA(B) (K(i) =47 +/- 4.4 nM) compared to GABA(A) (K(i) = 430 +/- 46 nM) binding sites. The compound was a full agonist at human recombinant GABA(B(1a,2)) receptors (EC(50) = 130 +/- 10 nM). In contrast, the metabolite AFPSoA was considerably more selective for binding to rat brain GABA(A) (K(i) = 37 +/- 3.1 nM) vs GABA(B) (K(i) = 6800 +/- 280 nM) receptors. In the mouse, high doses (1-8 mmol kg(-1)) of AFPSiA induced a rapid and mild hypothermia followed by a profound and sustained hypothermia at the higher doses tested (6 and 8 mmol kg(-1)). This effect was unaffected by the selective GABA(B) receptor antagonist CGP62349. AFPSoA (1 and 2 mmol kg(-1)) produced transient and moderate hypothermia while the hypothermic response was considerably larger at 4 mmol kg(-1).It is concluded that AFPSiA inhibits but does not abolish TLOSRs in the dog. High doses of the compound induce hypothermia in the mouse, which probably is attributable to activation of the GABA(A) receptor. The latter effect may be caused both by AFPSiA and its oxidised sulphonic acid metabolite AFPSoA.

Relationship between the mechanism of gastro-oesophageal reflux and oesophageal acid exposure in patients with reflux disease

This study investigated the relationship between the oesophageal acid exposure time and the underlying manometric motor events in patients with gastro-oesophageal reflux disease (GORD). In 31 patients, 3-hour oesophageal motility and pH were measured after a test meal. Ten patients underwent 24-hour ambulatory manometry and pH recording. In the 3-hour postprandial study, of 367 reflux episodes 79% was associated with a transient lower oesophageal sphincter relaxation (TLOSR), 14% with absent basal lower oesophageal sphincter (LOS) pressure and the remaining 7% with other mechanisms, representing 62, 28 and 10% of the acid exposure time, respectively. Acid reflux duration per motor mechanism was longer for absent basal LOS pressure than for TLOSR (189 +/- 23 s and 41 +/- 5 s, respectively, P < 0.001). In the 24-hour ambulatory study, the contribution of TLOSRs to reflux frequency vs acid exposure time were 65 vs 54% interprandially and 74 vs 53% after the meal. During the night, absence of basal LOS pressure accounted for 36% of reflux events representing 71% of acid exposure time. In conclusion, the duration of oesophageal acid exposure following a TLOSR is shorter than reflux during absent basal LOS pressure. TLOSRs are, the major contributor to oesophageal acid exposure during the day. At night, however, reflux during absent basal LOS pressure is the major contributor to acid exposure.

Inhibition of transient lower esophageal sphincter relaxations by electrical acupoint stimulation

Acupuncture has been shown to modulate visceral sensation and function. Traditionally, stimulation at the Neiguan (pericardial meridian) has been used to treat upper gastrointestinal symptoms. Some of the effects of acupuncture may be mediated through release of endogenous opioids and are reversed by naloxone. Gastric distension is the major trigger for transient lower esophageal sphincter (LES) relaxations (TLESRs). The aim of this study was to investigate the effect of electric stimulation at the Neiguan and naloxone on the TLESRs. In 14 healthy volunteers, electrical acupoint stimulation was applied at the Neiguan and a sham point on the hip in randomized order on the same day. In 12 healthy volunteers, the effects of naloxone (80 microg/kg iv bolus injection) and saline on electrical acupoint stimulation were compared on separate days at least 1 wk apart. Esophageal motility was measured during distension of the proximal stomach with 500 ml of air using a barostat balloon. Electric acupoint stimulation at the Neiguan decreased the rate of TLESRs by approximately 40% from a median of 6/h to 3.5/h (P < 0.02). Acupoint stimulation had no effect on basal LES pressure, the residual LES pressure during TLESRs, the duration of TLESRs, or gastrointestinal symptoms of fullness, bloating, discomfort, or nausea. The effect of acupoint stimulation was not inhibited by naloxone. Electric acupoint stimulation at the Neiguan significantly inhibits the frequency of TLESRs in response to gastric distention in healthy subjects. This effect does not appear to be mediated through mu-opioid receptors.

The lower oesophageal sphincter

The lower oesophageal sphincter (LOS) is a specialized segment of the circular muscle layer of the distal oesophagus, accounting for approximately 90% of the basal pressure at the oesophago-gastric junction. Together with the crural diaphragm, it functions as an antireflux barrier protecting the oesophagus from the caustic gastric content. During swallowing or belching, the LOS muscle must relax briefly in order to allow passage of food or intragastric air. These swallow-induced and prolonged transient lower oesophageal sphincter relaxations (TLOSRs) respectively result from activation of the inhibitory motor innervation of the sphincter. Both in man and animals, the main neurotransmitter released by the inhibitory neurones is nitric oxide. The two typical examples of dysfunction of the LOS are achalasia and gastro-oesophageal reflux disease (GORD). Achalasia is characterized by reduction or even absence of the inhibitory innervation to the LOS, leading to impaired LOS relaxation with dysphagia and stasis of food in the oesophagus. On the contrary, GORD results from failure of the antireflux barrier, with increased exposure of the oesophagus to gastric acid. This leads to symptoms such as heartburn and regurgitation, and in more severe cases to oesophagitis, Barrett's oesophagus and even carcinoma. To date, TLOSRs are recognized as the main underlying mechanism, and may represent an important target for treatment. More insight in the pathogenesis of both diseases will undoubtedly lead to new treatments in the near future.

[Reflux esophagitis]

Gastroesophageal reflux disease (GERD) is one of the most prevalent diseases in the industrialized countries. Approximately 15-25% of adults suffer from reflux symptoms, characterized mainly by heartburn and/or regurgitation. Currently, antisecretory medication with proton pump inhibitors (PPI) or antireflux surgery are the established options for GERD-treatment. PPI are the therapeutic gold standard in acute, long-term or on-demand therapy of GERD. Since PPI do not restore the antireflux barrier but merely suppress acid secretion a life-long tablet adherence is required in most cases. In view of limitations of PPI and the potential risks of laparoscopic surgery, several endoscopic antireflux techniques were developed and may evolve as a valuable third option. However, so far objective long-term data are lacking for choosing the appropriate patient who will benefit most from endoluminal antireflux therapy.

Reproducibility of meal-induced transient lower oesophageal sphincter relaxations in patients with gastro-oesophageal reflux disease

AIM

To calculate the number of subjects required in trials investigating drugs reducing the number of transient lower oesophageal sphincter relaxations (TLOSRs), the inter- and intra-individual variability of TLOSRs were determined, using meal ingestion as a trigger of TLOSRs and reflux.

METHODS

A total of 23 gastro-oesophageal reflux disease (GORD) patients with no to grade B oesophagitis and a hiatal hernia < or =3 cm underwent oesophageal manometry and pHmetry 1 h before and 3 h after ingestion of a solid meal on two separate days approximately 4 weeks apart. Reflux episodes and the underlying mechanisms and the number of TLOSRs were evaluated.

RESULTS

The number of TLOSRs, reflux episodes and % time with pH < 4 after meal ingestion did not differ significantly between the two sessions. The intra-individual variation of TLOSRs in the 3 h postprandial period (24.4) was smaller compared with the inter-individual variation (47.5). Transient lower oesophageal sphincter relaxations were the predominant cause of reflux accounting for 61 +/- 7 and 70 +/- 5% of the reflux episodes in visits 1 and 2, respectively.

CONCLUSIONS

These data for the first time provide information on the variability of TLOSRs and reflux evoked by meal ingestion, which is of crucial importance for the design and power calculations of future clinical studies evaluating the efficacy of new drugs targeting TLOSRs.

Molecular structure and physiological functions of GABA(B) receptors

GABA(B) receptors are broadly expressed in the nervous system and have been implicated in a wide variety of neurological and psychiatric disorders. The cloning of the first GABA(B) receptor cDNAs in 1997 revived interest in these receptors and their potential as therapeutic targets. With the availability of molecular tools, rapid progress was made in our understanding of the GABA(B) system. This led to the surprising discovery that GABA(B) receptors need to assemble from distinct subunits to function and provided exciting new insights into the structure of G protein-coupled receptors (GPCRs) in general. As a consequence of this discovery, it is now widely accepted that GPCRs can exist as heterodimers. The cloning of GABA(B) receptors allowed some important questions in the field to be answered. It is now clear that molecular studies do not support the existence of pharmacologically distinct GABA(B) receptors, as predicted by work on native receptors. Advances were also made in clarifying the relationship between GABA(B) receptors and the receptors for gamma-hydroxybutyrate, an emerging drug of abuse. There are now the first indications linking GABA(B) receptor polymorphisms to epilepsy. Significantly, the cloning of GABA(B) receptors enabled identification of the first allosteric GABA(B) receptor compounds, which is expected to broaden the spectrum of therapeutic applications. Here we review current concepts on the molecular composition and function of GABA(B) receptors and discuss ongoing drug-discovery efforts.

Pathophysiological characteristics of patients with non-erosive reflux disease differ from those of patients with functional heartburn

BACKGROUND

Patients with endoscopy-negative heartburn can be subdivided into non-erosive reflux disease and functional heartburn on the basis of abnormal and normal, respectively, oesophageal acid exposure. Different pathophysiological characteristics could explain the reportedly low efficacy of proton pump inhibitors in functional heartburn.

AIM

To assess if non-erosive reflux disease and functional heartburn are pathophysiologically distinguishable.

METHODS

Oesophageal manometry and pH-monitoring were performed in 145 patients with endoscopy-negative heartburn, in 72 patients with erosive reflux disease, in 58 patients with complicated reflux disease, and in 60 controls.

RESULTS

Patients with non-erosive reflux disease (84 cases) and functional heartburn (61 cases) differed with regard to the prevalence of hiatal hernia (49% vs. 31%, P = 0.008), the mean lower oesophageal sphincter tone (18.5 vs. 28.4 mmHg, P < 0.05), and the number of upright diurnal acid refluxes lasting more than 5 min (3.6 vs. 0.37, P < 0.05). The results were very close in thenon-erosive reflux disease, erosive reflux disease and complicated reflux disease groups, whilst patients with functional heartburn were indistinguishable from controls.

CONCLUSIONS

Pathophysiological characteristics typical of gastro-oesophageal reflux disease are found in patients with non-erosive reflux disease but not in patients with functional heartburn. This could explain the reportedly low efficacy of proton pump inhibitors in functional heartburn and suggests considering different management strategies.

An experimental model for the study of transient lower oesophageal sphincter relaxation and motor function of the proximal stomach in humans

A simple and reliable experimental model would be useful in human research on new drugs which target transient lower oesophageal sphincter (LOS) relaxation. The aim was to investigate the effect of repeated distensions on the rate of transient LOS relaxation, LOS pressure and motor function of the proximal stomach. Twelve healthy subjects were studied with a multilumen manometric assembly incorporating a sleeve sensor for the LOS and a bag positioned in the proximal stomach and connected to a barostat. Intrabag volume was set at 75% of the threshold for gastric discomfort and maintained for two 30-min distension periods separated by a 45-min washout with the bag deflated. The studies lasted 145 +/- 2 min. The rate of transient LOS relaxations was similar during the two distensions, 3.5;2-4 vs 3;2.5-4 (median;interquartile range) and so was LOS pressure. Baseline intrabag pressure, as a measure of gastric tone, and the number of pressure waves, as a measure of phasic contractions, were also similar, 11.3;9.3-12.3 mmHg vs 10.8;9.3-12.5 mmHg and 16;13-28 mmHg vs 19;15-29 mmHg, respectively. Our model allows to perform 1-day studies which can assess two experimental conditions on transient LOS relaxations and motor function of the proximal stomach within an acceptable time span.

Mechanoreceptors of the proximal stomach: Role in triggering transient lower esophageal sphincter relaxation

BACKGROUND AND AIMS

The role of fundic tension and stretch mechanoreceptors in triggering transient lower esophageal sphincter (LES) relaxation is still unknown. This information would be useful for the development of effective pharmacologic strategies. To elucidate this topic, gastric contractile activity was modified during isovolumetric gastric distention at 2 different volumes.

METHODS

LES (Dentsleeve) and gastric (barostat) motility were recorded in 21 healthy subjects during studies comprising two 30-minute isovolumetric gastric distentions (placebo and glucagon or erythromycin). Glucagon (bolus of 4.8 microg/kg plus infusion of 9.6 microg x kg(-1) x h(-1)) was administered at high intragastric volume (i.e., 75% of the threshold volume for discomfort; n = 7) and erythromycin (3 mg/kg) at high (n = 7) and low intragastric volume (i.e., at perception threshold; n = 7).

RESULTS

Glucagon decreased (P < 0.05) baseline intragastric pressure and abolished gastric contractions (0 vs. 16.7 +/- 2.3), whereas erythromycin increased (P < 0.05) baseline pressure and doubled (P < 0.05) the rate of gastric contractions at both volumes. Neither drug affected the rate of transient LES relaxations. Low intragastric volume induced a lower rate of transient LES relaxations (1.7 +/- 0.3 vs. 5.7 +/- 1.1; P < 0.01) and gastric contractions (11.8 +/- 2.5 vs. 20.5 +/- 3.1; P < 0.05) compared with high volume but similar baseline intragastric pressure (10.6 +/- 0.6 vs. 11.9 +/- 0.9 mm Hg).

CONCLUSIONS

Stretch receptors (gastric volume) seem to be more relevant than tension receptors in triggering transient LES relaxation.

Pediatric gastroesophageal reflux disease???current perspectives

PURPOSE OF REVIEW

Although heartburn and regurgitation are common manifestations of gastroesophageal reflux disease (GERD), otolaryngologic or respiratory symptoms may be the only indication of GERD. This review focuses on the recent developments in the pathophysiology, diagnosis, and treatment of GERD and their implications in pediatrics.

RECENT FINDINGS

Newer diagnostic modalities include intraesophageal impedance and Bravo wireless pH monitoring. Impedance technology measures both acid and non-acid reflux, whereas the Bravo capsule allows prolonged pH monitoring under more physiologic conditions. In managing children with GERD, there is increasing evidence that they need higher dosages of acid suppressive therapy to achieve clinical response. Alternative therapeutic options are also currently being explored, including pharmacotherapy that targets the primary mechanism for GERD. Endoluminal therapy for GERD in adults as an alternative to surgery has been an exciting development. At present, two of these procedures, Stretta (using radiofrequency energy) and Endocinch (gastroplication), have been approved by the Food and Drug Administration for use in adults.

SUMMARY

Impedance technology has increased our understanding of acid and nonacid reflux; however, normal values for children are not yet established. There are also limitations to the applicability of the new endoluminal therapies in children. Further research is needed before these developments can be recommended for use in pediatric practice.

Gastroesophageal Reflux Disease

Gastroesophageal reflux disease is a common, usually lifelong, disorder resulting from chronic abnormal exposure of the lower esophagus to gastric contents. Motor dysfunction of the lower esophageal sphincter is the primary cause of this disease. At this writing, no medical therapies can completely resolve abnormal lower esophageal sphincter function; therefore, the treatment of gastroesophageal reflux disease centers on suppression of intragastric acid secretion. Available acid-suppressant medications include proton pump inhibitors, H2-receptor antagonists, and antacids. Of these, the proton pump inhibitors are recognized generally as the mainstays of both short-term and long-term therapy for gastroesophageal reflux disease. All have a low incidence of side effects and are well tolerated by most patients. Five proton pump inhibitors are available currently for patients with gastroesophageal reflux disease. Of these, esomeprazole has shown greater efficacy in controlling intragastric acidity than the others. For patients with erosive esophagitis, esomeprazole has demonstrated higher healing rates and more rapid sustained resolution of heartburn than omeprazole or lansoprazole after up to 8 weeks of once-daily treatment. Because new therapies for gastroesophageal reflux disease are highly effective, patients can be reassured that their disease will be well controlled and their symptoms resolved with a safe and appropriate treatment.

Gastroesophageal reflux disease

Globally, gastroesophageal reflux disease (GERD) remains a common and important clinical disorder. This review summarizes the major advances in the understanding and treatment of GERD that have been made in the past 12 months. Epidemiologic studies have yielded additional data on the clinical presentation and natural history of GERD in the East. Further insights have been presented on the pathogenesis of GERD, including the immunoregulatory environment of GERD, the neurophysiology of transient lower esophageal sphincter relaxation (TLESR), the mechanics of the esophagogastric junction as well as the influence of Helicobacter pylori. Diagnostically, a new acid exposure sensor may be a helpful cost-effective tool. Developments have been made in pharmacotherapy for TLESR. There is ongoing interest in endoscopic therapy and further developments have been made in laparoscopic fundoplication. The cost-effectiveness of several management strategies has been evaluated, aiming to reduce the cost impact of GERD on the health care system.

Pharmacokinetics of a single oral dose of baclofen in pediatric patients with gastroesophageal reflux disease

Transient relaxation of the lower esophageal sphincter (TLESR) is the predominant mechanism of gastroesophageal reflux (GER) in adults and children. Baclofen [4-amino-3-(p-chlorophenyl)-butanoic acid], a gamma-aminobutyric acid (GABA)-B receptor agonist used for the management of spasticity, has been recently shown to significantly inhibit GER in healthy adults without any relevant side effects. The objective of this study was to evaluate the pharmacokinetics of baclofen in a pediatric population with GER disease. In an open-label single-dose pharmacokinetic study, eight children with the diagnosis of GER made on clinical grounds received an oral dose of baclofen, 2.5 mg. Blood samples were drawn from an indwelling venous catheter, and urine was collected during a postdose period of 8 hours. The concentration of baclofen in these body fluids was determined using a validated high-performance liquid chromatography (HPLC) method with electrochemical detection after OPA-sulfite derivatization. Pharmacokinetic data were analyzed using the nonlinear regression program Scientist. Serum concentration-time curves could be best described using a two-compartment open model with a lag time. Mean plasma clearance (Cl) was 315.9 mL/h/kg; volume of distribution (Vd) was 2.58 L/kg; and half-life (T(1/2)beta) was 5.10 hours. No side effects were noted. As half-lives were comparable with those found in adult studies, the risk for accumulation seems not greater in children than in adults. Body composition can have a strong influence on the Vd of baclofen and, therefore, on the dose needed to obtain therapeutic plasma levels. Dosing according to clearly defined age groups with the help of therapeutic drug monitoring seems preferable. In view of the negative correlation between body weight and Vd, dosing according to body weight using adult pharmacokinetic data does not seem an effective way for using baclofen in children.

Plexiglas (polymethylmethacrylate) implantation: technique, pre-clinical and clinical experience

Over the past few decades, a great scientific effort has been made to treat gastroesophageal reflux disease (GERD). This reflects a trend in modem medicine toward optimizing quality of life, reducing health-related lost working hours, and minimizing costs of chronic treatments. It also reflects a revived interest in diseases that can be studied using novel equipment and that can be cured using minimally invasive techniques. In an effort to further minimize surgical trauma, novel endoscopic techniques are beginning to challenge the standard therapeutic approach to GERD.