Mechanism Of Gastro-oesophageal Reflux Research Articles

Inhibition of Transient Lower Esophageal Sphincter Relaxation and Gastroesophageal Reflux by Metabotropic Glutamate Receptor Ligands

Transient lower esophageal sphincter relaxation (TLESR) is the major mechanism of gastroesophageal acid reflux. TLESR is mediated via vagal pathways, which may be modulated by metabotropic glutamate receptors (mGluRs). Group I mGluRs (mGluR1 and 5) have excitatory effects on neurons, whereas group II (mGluR2 and 3) and group III (mGluR4, 6, 7, and 8) are inhibitory. This study determined the effect of mGluRs on triggering of TLESR and reflux in an established conscious ferret model. Esophageal manometric/pH studies were performed in ferrets with chronic esophagostomies. TLESR were induced by a gastric load of 25 mL glucose (pH 3.5) and 30 mL air. In control treated animals, gastric load induced 3.52 +/- 0.46 TLESRs per 47-minute study, 89.7% of which were associated with reflux episodes (n = 16). The mGluR5 antagonist MPEP inhibited TLESR dose dependently, with maximal 71% +/- 7% inhibition at 35 micromol/kg (n = 9; P < .0001). MPEP also significantly reduced reflux episodes (P < .001) and increased basal lower esophageal sphincter pressure (P < .05). MPEP inhibited swallowing dose dependently, suggesting a common action on trigger mechanisms for swallowing and TLESR. The more selective analogue, MTEP, had more potent effects (90% +/- 6% inhibition TLESR at 40 micromol/kg; n = 8; P < .0001). In contrast, the group I agonist DHPG tended to increase TLESR. The group II agonist (2R, 4R)-APDC was ineffective, whereas the group III agonist L-(AP4 slightly reduced TLESR (33% at 11 micromol/kg; P < .05). The selective mGluR8 agonist (S)-3, 4-DCPG inhibited TLESR by 54% at 15 micromol/kg (P < .01). mGluR5 antagonists potently inhibit TLESR and reflux in ferrets, implicating mGluR5 in the mechanism of TLESR. mGluR5 antagonists are therefore promising as therapy for patients with GERD.

Subcutaneous epinephrine administration decreases lower oesophageal sphincter pressure and gastro-oesophageal pressure gradient in children under general anaesthesia

Background and objective: Children are vulnerable to regurgitation with a relatively high incidence of aspiration during general anaesthesia which is attributed to the high intragastric pressure, a short oesophagus, an immature laryngeal reflex and incomplete lower oesophageal sphincter muscle function. Subcutaneous administration of epinephrine is generally used in surgery to decrease bleeding due to local vasoconstriction. The effect of epinephrine on the sphincter muscle tone was investigated during general anaesthesia in children. Methods: Ten children scheduled for skin graft or plastic surgery of the ear were studied. A gastrointestinal pressure sensor was inserted nasally, and the intraluminal pressures of the lower oesophagus, lower oesophageal sphincter and stomach were monitored under sevoflurane, nitrous oxide anaesthesia. The effect of epinephrine on the lower oesophageal sphincter muscle tone was measured. Results: The resting pressure of the lower oesophageal sphincter muscle tone significantly decreased from 4.56 ± 1.85 to 3.79 ± 1.11 kPa after 3 μg kg−1 epinephrine for 4 min. The barrier pressure is the difference between the lower oesophageal sphincter and intragastric pressure, and that decreased to 1.23 ± 1.17 kPa from the 2.07 ± 1.77 kPa resting level. The observations implied that epinephrine had a long-lasting relaxing effect on lower oesophageal sphincter muscle in children. Conclusions: The observations may give some explanation about the mechanism of gastro-oesophageal reflux during general anaesthesia, especially in the participation of the adrenergic receptors.

The anti-reflux barrier and mechanisms of gastro-oesophageal reflux

The lower oesophageal sphincter (LOS) is the major component of the anti-reflux barrier. The majority of reflux episodes occur because of intermittent brief complete lower oesophageal sphincter relaxations, transient LOS relaxations, rather than from chronic absence of LOS pressure. Recent advances in the understanding of the neural mechanisms and the receptors involved in the triggering of transient LOS relaxations have provided new insights into their control and offer the potential for the development of pharmacological therapy of reflux based on control of these events. Extrinsic support by the crural diaphragm is also important and loss of this support through development of hiatus hernia significantly compromises LOS function. This chapter reviews the components of the anti-reflux barrier, the patterns and mechanisms of LOS dysfunction underlying reflux episodes, and the interplay between sphincteric and non-sphincteric factors.

Cholinergic blockade inhibits gastro-oesophageal reflux and transient lower oesophageal sphincter relaxation through a central mechanism

BACKGROUNDAtropine, an anticholinergic agent with central and peripheral actions, reduces gastro-oesophageal reflux (GOR) in normal subjects and patients with gastro-oesophageal reflux disease (GORD) by inhibiting the frequency of transient lower...

Prevalence and mechanisms of gastro-oesophageal reflux in adult cystic fibrosis patients.

Gastro-oesophageal reflux (GOR) occurs frequently in children with cystic fibrosis (CF) but has not been studied in adult CF. We surveyed such symptoms by structured questionnaire in 50 adult CF patients (mean age 26 years, range 16-50; 24 male) and performed oesophageal manometry and 24-hour pH recording in 10 who had reflux symptoms (mean age 28 years, range 21-35; 8 men). 47 patients (94%) had upper gastrointestinal symptoms: 40 (80%) heartburn (27 worse when supine); 26 (52%) regurgitation; and 28 (56%) dyspepsia. At oesophageal manometry, lower oesophageal sphincter barrier pressure (LOSBP) was subnormal in 6 of the 10 patients and 3 had uncoordinated peristalsis in the mid oesophagus. 8 patients had raised DeMeester scores, indicating significant GOR. Those patients with a LOSBP < 5mm Hg had a higher DeMeester score (mean 81.0, range 47.9-128.8) than the patients with a normal LOSBP (26.9, 8.7-56.5; p < 0.002). These results show that adult CF patients have high rates of GOR symptoms, diminished LOSBP, and acid reflux.

Motor events underlying gastro-oesophageal reflux in ambulant patients with reflux oesophagitis.

Information on the mechanism of gastro-oesophageal reflux in patients with reflux disease is limited largely to studies in resting recumbent subjects. Evidence exists that both posture and physical activity may influence reflux. The aim of this study was to investigate reflux mechanisms in ambulant patients with reflux oesophagitis. Concurrent ambulatory oesophageal manometry and pH monitoring were performed in 11 ambulant patients with erosive oesophagitis. Lower oesophageal sphincter (LOS) pressure was monitored with a perfused sleeve sensor. Recordings were made for 90 min before and 180 min after a meal. At set times patients sat in a chair or walked. LOS pressure was < or = 2 mmHg at the time of reflux for 98% of reflux episodes. Transient LOS relaxation was the most common pattern overall and the predominant pattern in seven patients, whilst persistently absent basal LOS pressure was the most common pattern in four patients. The pattern of LOS pressure was not altered by the presence of hiatus hernia or by walking. Straining occurred at the onset of 31% of acid reflux episodes but often followed the development of an oesophageal common cavity. The occurrence of straining was not influenced by walking. In ambulant patients with reflux oesophagitis: (1) LOS pressure is almost always absent at the time of reflux, usually because of transient LOS relaxation, (2) persistently absent basal LOS pressure is an important mechanism of reflux in a few patients, (3) straining may help to induce acid reflux in a variable proportion of occasions and may in some instances be a response to gas reflux, and (4) walking does not influence the occurrence of reflux or its mechanisms.

Effect of cholecystokinin on lower oesophageal sphincter pressure and transient lower oesophageal sphincter relaxations in humans.

The effect of cholecystokinin (CCK) on the lower oesophageal sphincter (LOS) pressure, frequency of transient LOS relaxations, and the number of reflux episodes was investigated in six healthy subjects. LOS pressure was recorded on four separate occasions during continuous intravenous infusion of either saline or CCK-33 in doses of 0.25, 0.5, or 1.0 Ivy Dog units per kg body weight per hour (IDU.kg-1.h-1) for 90 minutes. Plasma CCK concentrations did not change during saline infusion, but increased significantly from 2.5 (0.3) pmol/l to steady state levels of 4.0 (0.4) pmol/l, 6.1 (0.4) pmol/l, and 9.3 (0.9) pmol/l respectively starting from 30 minutes. LOS pressure did not change significantly during infusion of saline or of CCK-33 at doses of 0.25 or 0.5 IDU.kg-1.h-1. However, a significant (p < 0.05) reduction in LOS pressure to a minimum level of 12 (4) mm Hg at 30 minutes compared with basal level (18 (4) mm Hg) and compared with saline was observed during infusion of CCK-33 at a dose of 1.0 IDU.kg-1.h-1. In addition, oesophageal motility and pH were recorded simultaneously in these six subjects on two separate occasions one hour before (fasting) and three hours during administration of a gastric load (dextrose 5%, pH 3) combined with continuous intravenous infusion of saline or CCK-33 at a dose of 1.0 IDU,kg-1.h-1. Plasma CCK concentrations did not change during the gastric load combined with saline, but increased significantly to a steady state level of 10.8 (0.8) pmol/l during intravenous infusion of CCK. The number of transient LOS relaxations increased significantly in the first hour during administration of the gastric load compared with fasting levels, both during saline infusion (fasting: 1.7 (0.6)/h, 1st hour: 4.3 (1.2)/h) and during CCK infusion (fasting: 1.7 (0.5)/h, 1st hour: 3.8 (0.7)/h). In the second and third hours the number of transient LOS relaxations fell to fasting levels in both experiments. No significant differences were observed in the number and type of transient LOS relaxations, mechanism of gastro-oesophageal reflux, or duration of acid exposure between the two experiments. It is concluded that in healthy subjects infusion of CCK-33 in a dose of 1.0 IDU.kg-1.h-1 significantly reduces LOS pressure but does not affect the frequency of transient LOS relaxations or acid exposure time during a continuous liquid gastric load.

Mechanisms of gastro-oesophageal reflux in cystic fibrosis.

Abnormal degrees of gastro-oesophageal reflux (GOR) were detected by 24 hour intraoesophageal pH measurement in 12 of 14 children (mean age 7.9 years; range 5 months-16 years) affected by cystic fibrosis and complaining of symptoms suggesting GOR. These patients underwent combined recording of distal oesophageal motility and intraluminal pH in order to investigate mechanisms of GOR. Inappropriate lower oesophageal sphincter relaxation was the most common mechanism of reflux in all patients. Other mechanisms (appropriate relaxation or lowered pressure of the lower oesophageal sphincter, increased intragastric pressure) were detected less frequently. Frequency of inappropriate lower oesophageal sphincter relaxations was significantly higher in patients with cystic fibrosis than in other study groups (symptomatic GOR, GOR disease complicated by respiratory complaints). Inappropriate lower oesophageal sphincter relaxations occurred with the same frequency in patients with cystic fibrosis and in a group of children with GOR disease complicated by oesophagitis. Abnormalities of distal oesophageal contractions such as decreased amplitude or uncoordinated waves were also recorded in cystic fibrosis patients. Seven patients with cystic fibrosis completed a therapeutic trial for eight weeks consisting of postural treatment and oral cisapride, a new prokinetic drug. The oesophageal acid exposure improved in only three patients. We conclude that pathologic GOR is commonly associated with cystic fibrosis. The predominant reflux mechanism in these patients is a transient inappropriate lower oesophageal sphincter relaxation rather than a low steady state basal lower oesophageal sphincter pressure.

Does body posture affect the incidence and mechanism of gastro-oesophageal reflux?

We studied eight patients with gastro-oesophageal reflux disease to compare the frequency and mechanism of reflux in the upright and supine positions. Simultaneous oesophageal manometry and pH studies were performed on two separate days in each subject in the fasting and postprandial periods. The frequency of reflux tended to be higher in the upright position. The most prevalent mechanism of reflux in either position was transient relaxation of the lower oesophageal sphincter. The frequency of transient lower oesophageal sphincter relaxation was higher in the upright than in the supine position. There was no difference in the total reflux time, acid clearance time, and number of reflux episodes lasting longer than five minutes in the two positions. We suggest that daytime reflux (upright) may be as important as night time (supine) reflux in the pathogenesis of reflux oesophagitis and needs to be considered when treating patients with reflux disease.

1 Recent views on the pathogenesis of gastro-oesophageal reflux disease

The pathogenesis of GORD depends on a mix of factors which vary amongst individual patients. The central issue in the pathogenesis of gastro-oesophageal reflux is understanding of the mechanisms that lead to reflux, since the effects of all other factors depend on this event. Consequently, new information and views about the mechanisms of gastro-oesophageal reflux have been presented in detail. This information suggests that defective lower oesophageal sphincter motility is the most important abnormality that underlies pathological gastro-oesophageal reflux. Two major forms of LOS dysfunction have been identified as responsible for pathological gastrooesophageal reflux in the horizontal position: (1) an excessively frequent rate of occurrence of transient LOS relaxations; and (2) defective basal LOS tone. Both of these dysfunctions appear to arise from abnormal neural control of the LOS, probably by the central nervous system. The effect of these LOS dysfunctions on gastro-oesophageal competence is probably significantly influenced by non-sphincteric factors, the most important of these apparently being hiatus hernia. Though there is currently poor understanding about the ways in which hiatus hernia impairs gastro-oesophageal competence, measurement techniques have now advanced sufficiently to allow significant accrual of knowledge in this field. p]Once reflux has occurred, the efficiency of oesophageal acid clearance plays a major role in determining the impact of reflux on the oesophageal mucosa. Recent studies have shown that oesophageal acid clearance depends on both effective volume clearance and neutralization by saliva of residual acid in the oesophageal lumen. The efficiency of oesophageal volume clearance of both simulated and real reflux has not been studied formally in GORD patients, but the high incidence of peristaltic dysfunction in reflux disease suggests that volume clearance will be defective in some patients. The limited information available about salivation in GORD patients suggests that salivary secretion is no different from that of age-matched controls, but that there is an agedependent loss of the salivary response to oesophageal acidification. This impairment of salivary response may produce an age-dependent decline of the efficiency of oesophageal acid clearance. p]Unusually aggressive refluxate and impaired mucosal resistance to injury have been proposed as significant variables which contribute to pathogenesis of reflux disease. The evidence for these factors is circumstantial and scanty. Their importance has probably been overestimated. p]There has been little progress recently in the understanding of factors that lead to disabling oesophagopharyngeal reflux. Significant advances are expected in this field with the application of a measurement approach that will allow recording of the mechanical events associated with regurgitation.