Assessment of neural inhibition of the lower esophageal sphincter in cats with esophagitis

Esophagitis in Cats and Dogs

Esophagitis in cats and dogs is a consequence of increased exposure of the esophageal mucosa to gastroduodenal reflux. Causes can include anesthesia-related reflux, frequent vomiting, or lodged foreign bodies. An exception is eosinophilic esophagitis, an emerging primary inflammatory disease of the esophagus with a presumed allergic etiology. Reflux esophagitis owing to lower esophageal sphincter incompetence is often suspected; a tentative diagnosis can be made by endoscopic assessment, wireless esophageal pH-monitoring, or histologic examination. Because it can be difficult to distinguish diet-responsive upper gastrointestinal disease from esophagitis, response to treatment with gastric acid suppressants is needed to confirm the tentative diagnosis.

Esophagogastric junction and esophageal body contraction metrics on high-resolution manometry predict esophageal acid burden

BACKGROUND

Distal contractile integral (DCI) and esophagogastric junction contractile integral (EGJ-CI) are high-resolution manometry (HRM) software metrics assessing esophageal motor function in gastroesophageal reflux disease (GERD).

METHODS

Patients undergoing HRM and ambulatory pH monitoring off antisecretory therapy prospectively completed symptom questionnaires assessing symptom burden and a global symptom score (GSS) at baseline and after GERD therapy. DCI<450 mm Hg/cm/s in ≥5 swallows diagnosed ineffective esophageal motility (IEM); proportions of failed (DCI<100 mm Hg/cm/s) and weak (DCI 100-450 mm Hg/cm/s) sequences were separately assessed. EGJ-CI assessed vigor of the EGJ barrier. Univariate and multivariate analyses addressed performance of esophageal body and EGJ metrics in predicting abnormal esophageal reflux burden, and symptom outcome from antireflux therapy.

KEY RESULTS

Of 188 patients (55.2 ± 0.9 year, 64% F), 42.6% had low EGJ-CI, and 25.0% had IEM. While low EGJ-CI was associated with abnormal reflux burden (P = 0.003), IEM alone was not (P = 0.2). Increasing proportions of failed swallows predicted abnormal AET better than the current IEM definition. Combined low EGJ-CI and IEM segregated abnormal total and supine acid burden compared to patients with normal EGJ-CI and no IEM (P ≤ 0.007 for each comparison). Medical therapy and surgical antireflux therapy were similarly effective in improving symptom burden; surgery resulted in better outcomes with low EGJ-CI (P ≤ 0.04), especially with intact esophageal body motor function (P = 0.02).

CONCLUSIONS & INFERENCES

While abnormal EGJ and esophageal body metrics are collectively associated with elevated esophageal reflux burden, increasing proportions of failed swallows are better predictors of reflux burden and outcome compared to the current IEM definition.

Classification of esophageal motor findings in gastro-esophageal reflux disease: Conclusions from an international consensus group

BACKGROUND

High-resolution manometry (HRM) has resulted in new revelations regarding the pathophysiology of gastro-esophageal reflux disease (GERD). The impact of new HRM motor paradigms on reflux burden needs further definition, leading to a modern approach to motor testing in GERD.

METHODS

Focused literature searches were conducted, evaluating pathophysiology of GERD with emphasis on HRM. The results were discussed with an international group of experts to develop a consensus on the role of HRM in GERD. A proposed classification system for esophageal motor abnormalities associated with GERD was generated.

KEY RESULTS

Physiologic gastro-esophageal reflux is inherent in all humans, resulting from transient lower esophageal sphincter (LES) relaxations that allow venting of gastric air in the form of a belch. In pathological gastro-esophageal reflux, transient LES relaxations are accompanied by reflux of gastric contents. Structural disruption of the esophagogastric junction (EGJ) barrier, and incomplete clearance of the refluxate can contribute to abnormally high esophageal reflux burden that defines GERD. Esophageal HRM localizes the LES for pH and pH-impedance probe placement, and assesses esophageal body peristaltic performance prior to invasive antireflux therapies and antireflux surgery. Furthermore, HRM can assess EGJ and esophageal body mechanisms contributing to reflux, and exclude conditions that mimic GERD.

CONCLUSIONS & INFERENCES

Structural and motor EGJ and esophageal processes contribute to the pathophysiology of GERD. A classification scheme is proposed incorporating EGJ and esophageal motor findings, and contraction reserve on provocative tests during HRM.

Effect of repeated cycles of acute esophagitis and healing on esophageal peristalsis, tone, and length

Severe esophagitis is associated with motor abnormalities in the esophageal body and lower esophageal sphincter. Reflux disease involves repeated episodes of mucosal inflammation and spontaneous or treatment-induced healing. The aims of this study were 1) to further assess changes induced by acute esophagitis on esophageal peristalsis, tone, and shortening and 2) to assess the effect of repeated sequences of acute esophagitis-healing on these motor parameters. Experiments were performed on adult cats. Esophageal manometry and barostat were performed before, 24 h after, and every 7 days after intraesophageal acid perfusion (0.1 N HCl, 80 min). Esophageal length was measured during manometry, and compliance of the esophageal body was assessed with barostat. The identical protocol was performed 8 and 16 wk after the first acid perfusion. The degree of esophageal mucosal damage was evaluated by endoscopy, histopathology, and myeloperoxidase activity. Acid perfusion induced severe esophagitis. At 24 h, distal peristaltic contractions disappeared, lower esophageal sphincter pressure was reduced by 60%, the esophagus length was 1-2 cm shorter, and esophageal compliance was reduced by 30%. Most parameters recovered in 4 wk. Subsequent repeated acute injuries induced similar endoscopic esophagitis but a different pattern of inflammatory infiltration and fibrosis in the mucosa and muscle layers, resulting in milder motor disturbances. Acute experimental esophagitis provokes severe but reversible hypomotility. Spaced repeated acute injuries provoke milder motor effects, suggesting an adaptive response.

Progress with novel pharmacological strategies for gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GORD) is a chronic disorder characterised by an increased exposure of the oesophagus to intragastric contents. Currently, GORD symptoms are maintained under control with antisecretory agents, mainly gastric proton pump inhibitors (PPIs). Although impaired oesophageal motility may partly underlie the pathophysiology of GORD, the use of prokinetic agents has been found to be unsatisfactory. To date, novel pharmacological approaches for GORD are mainly related to the control of transient lower oesophageal sphincter (LOS) relaxations (TLOSRs). The majority of patients with GORD have reflux episodes during TLOSRs, which are evoked by gastric distension, mainly occurring after ingestion of a meal. Patients with reflux disease with normal peristalsis and without or with mild erosive disease could potentially benefit from anti-TLOSR therapy. This therapy might also be of value to treat some severe forms of esophagitis in combination with PPIs. GABA-B-receptor agonists are the most promising class of agents identified so far for TLOSR control. The GABA-B-receptor agonist, baclofen, is the most effective compound in inhibiting TLOSRs in humans. Since baclofen has several CNS adverse effects, novel orally available GABA-B agonists are needed for effective and well tolerated treatment of GORD. Endogenous or exogenous cholecystokinin (CCK) causes a reduction in LOS pressure, an increase in TLOSR frequency and a reduction in gastric emptying. In healthy volunteers and patients with GORD, loxiglumide, a selective CCK1-receptor antagonist, was found to reduce the rate of TLOSRs, although its effect on postprandial acid reflux may be modest. Orally effective CCK antagonists are not marketed to date. The anticholinergic agent atropine, given to healthy volunteers and patients with GORD, markedly reduced the rate of TLOSRs. Because of severe gastrointestinal (and other) adverse effects of anticholinergics, including worsening of supine acid clearance and constipation, it is unlikely that this class of drugs will have a future as anti-TLOSR agents on a routine basis. In spite of their effectiveness in reducing TLOSR rate, untoward adverse effects, such as addiction and severe constipation, currently limit the use of morphine and other opioid mu-receptor agonists. The same applies to nitric oxide synthase inhibitors, which are associated with marked gastrointestinal, cardiovascular, urinary and respiratory adverse effects. Animal studies provide promising evidence for the use of cannabinoid receptor 1 agonists, by showing potent inhibition of TLOSRs in the dog, thus opening a new route for clinical investigation in humans. A better understanding of TLOSR pathophysiology is a necessary step for the further development of novel drugs effective for anti-reflux therapy.

Pathogenesis of Gastroesophageal Reflux Disease

The pathophysiology of reflux esophagitis involves contact of the esophageal epithelium with acid-pepsin in the refluxate. For this contact to occur with sufficient duration, there must either be a combination of defects in antireflux and luminal clearance mechanisms for acid-pepsin to overwhelm a previously healthy epithelium or primary defects within the epithelium develop that subsequently enable 'normal' acid contact times to become damaging to the epithelium. This report examines these 2 pathways to reflux esophagitis and questions the causative role attributed to some phenomena. In either case, the final common pathway for the clinical expression of reflux esophagitis is by damage to the esophageal epithelium that is responsible for the development of heartburn and/or esophageal necrosis and inflammation.

Pathogenesis of gastroesophageal reflux disease

The pathophysiology of GERD involves contact of the esophageal epithelium with acid/pepsin in the refluxate. For this contact to occur with sufficient duration, there must be a combination of defects in antireflux and luminal clearance mechanisms for acid/pepsin to overwhelm an intact epithelium, or defects within the epithelium develop that subsequently enable normal acid contact times to become damaging to the epithelium. In either case, the final common pathway is damage to the esophageal epithelium--damage that is reflected in the development of heartburn, esophageal necrosis and inflammation, or both.

Overview of the mechanisms of gastroesophageal reflux

Reflux of acidic gastric contents through the esophagogastric junction into the esophageal lumen occurs in everyone nearly every day. The esophagogastric junction is composed of several structural components that contribute to its function as the primary antireflux barrier. Only when 1 or more of these components fail does reflux esophagitis develop. The initial focus of this review is on transient lower esophageal sphincter relaxations, a vagally mediated reflex arc that accounts for almost all reflux events in healthy individuals and the majority of reflux events in those with reflux esophagitis. The association of erosive esophagitis with low or absent (incompetent) lower esophageal sphincter (LES) pressure and anatomic disruptions of the esophagogastric junction, such as hiatal hernia, are also important, especially with respect to whether the LES dysfunction and hernia are the cause or the consequence of erosive disease.

Decreased sympathetic inhibition in gastroesophageal reflux disease

This study was undertaken to evaluate autonomic nervous system function in patients with gastroesophageal reflux disease. Based on clinical criteria, 28 consecutive patients with no history of heart, metabolic, or neurologic disease (mean age 41 y, range 20-62 y) reporting with upper gastrointestinal symptoms typical of gastroesophageal reflux underwent esophageal manometry, ambulatory 24-hour pH study with electrocardiographic monitoring, power spectral analysis of heart rate variability, and cardiovascular tests. Twelve healthy subjects served as controls. A positive result of prolonged esophageal pH study (pH in the distal esophagus less than 4, lasting more than 4.2% of recording time) was observed in 21 patients (reflux group); seven patients were categorized in the nonreflux group. No patient showed arrhythmias or any correlation between heart rate variability changes during electrocardiographic monitoring and episodes of reflux (pH less than 4, lasting more than 5 minutes). A decrease of sympathetic function occurred only in the reflux group (p <0.05) supported by the lower increase of systolic/diastolic blood pressure at sustained handgrip. No other cardiovascular tests showed statistically significant differences in the control or nonreflux groups. Total time reflux showed an inverse correlation with sympathetic function in the reflux group (r = -0.415, p <0.028). We concluded that there is some evidence for a slightly decreased sympathetic function in patients with gastroesophageal reflux disease that is inversely correlated with total time reflux. In these patients, decreased sympathetic function may cause dysfunction of intrinsic inhibitory control with increased transient spontaneous lower-esophageal sphincter relaxations, thus resulting in gastroesophageal reflux disease.

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.

Effect of an o-raffinose cross-linked haemoglobin product on oesophageal and lower oesophageal sphincter motor function

The present experiments evaluate the effects on oesophageal motility of an o-raffinose cross-linked haemoglobin-based oxygen carrier (HBOC) purified from outdated donated human blood cells (HemolinkTM), with attention to dose-response (0.6-2.4 g kg-1), oxygenation status and low molecular weight components (4.4-36.4% 64 kDa or less). In ketamine-anaesthetized cats, lower oesophageal sphincter (LES) function and oesophageal peristalsis were monitored 0.5 h before, during and up to 3.5 h after HBOC infusion, and in some cats at 24 h. (1) All products significantly inhibited LES relaxation and increased peristaltic velocity in the distal smooth muscle oesophagus, without consistently altering resting LES pressure. (2) Effects on peristaltic velocity reached a maximum at the smallest dose, whereas the effects on LES relaxation had a maximum effect at 1.2 g kg-1. (3) Effects were not significantly altered by the haemoglobin oxygenation status or presence of low molecular weight components. (4) Repetitive oesophageal contractions occurred. In the cat, an o-raffinose cross-linked human haemoglobin product produces changes in oesophageal body and LES function, which are independent of the HBOC oxygenation status and composition of the low molecular weight components tested. Changes may persist for at least 24 h. These motility changes are likely due to scavenging of nitric oxide by the haemoglobin.

Oesophagitis-induced changes in capsaicin-sensitive tachykininergic pathways in the ferret lower oesophageal sphincter

Prolonged oesophageal acidification may impair lower oesophageal sphincter (LOS) function in reflux disease. The aim of this study was to investigate aspects of altered LOS innervation in a model of oesophagitis. Oesophagitis was induced by acid (HCl, 0.15 M) and pepsin (0.1% w/v) infusions in anaesthetized ferrets. LOS muscle strip responses to the following stimuli were measured in vitro from control and acid/pepsin-treated ferrets: electrical field stimulation (EFS; 1-50 Hz), potassium chloride KCl; 20 mM), substance P, [beta-Ala8]-neurokinin A 4-10, [Sar9, Met (O2)11]-substance P (all 10(-10) to 10(-6) M) and capsaicin (10(-8) to 10(-6) M). LOS relaxation occurred in response to all stimuli except [beta-Ala8]-neurokinin A 4-10, which evoked contraction. In muscle strips from acid/pepsin-treated animals there were no differences in amplitude or sensitivity of relaxation following EFS, KCl or substance P vs controls. However, the inhibitory response to capsaicin was increased four-fold (10(-8) M; P < 0.05) and an increased sensitivity of the inhibitory response to [Sar9, Met (O2)11]-substance P occurred (pD2 = 8.64 +/- 0.12 acid/pepsin-treated vs 7.94 +/- 0.24 control, P < 0.05). We conclude that in acute oesophagitis, increased sensitivity of capsaicin-activated inhibitory pathways occurs in which activation of NK-1 receptors plays an integral role in the ferret LOS.

Lower oesophageal sphincter responses to noxious oesophageal chemical stimuli in the ferret: involvement of tachykinin receptors

Repeated oesophageal acidification is a definitive feature of gastro-oesophageal reflux disease, which in turn is caused by relaxation of the lower oesophageal sphincter (LOS). This study in anaesthetised ferrets investigates the reflex pathways involved in effects of oesophageal acidification on motor function of the LOS, with particular focus on the role of tachykinins. LOS pressure was monitored with a perfused micromanometric sleeve assembly. Oesophageal acidification reduced LOS pressure by 48 +/- 5% until washout with saline. This reduction became larger with repeated tests, and was unaffected in amplitude by acute bilateral vagotomy, although the response became slower in onset. Intra-oesophageal capsaicin (0.5% solution) caused a 68 +/- 17% decrease in LOS pressure which remained unchanged with repeated tests. The NK-1 receptor antagonist CP96,345 (1-5 mg/kg intravenous (i.v.) blocked the post-vagotomy LOS responses to both intra-luminal acid and capsaicin. Close intra-arterial (i.a.) injections of capsaicin (1-100 micrograms) gut induced LOS relaxation which was neither vagally nor NK-1 receptor-mediated. Substance P or the selective NK-1 receptor agonist [Sar9, Met(O2)11] substance P (25-500 ng close i.a.) caused a biphasic LOS response, consisting of initial brief contraction followed by prolonged, dose-dependent relaxation. Tetrodotoxin (10 micrograms/kg close i.a.) changed the biphasic response to substance P to excitation only. The neurokinin-1 (NK-1) receptor antagonist CP96,345 (0.3-10 mg/kg i.v.) dose-dependently reduced the inhibitory response to substance P. The excitatory phase of the response to substance P was larger and prolonged after guanethidine (5 mg/kg, i.v.), or propranolol (1 mg/kg, i.v.). L-NAME (100 mg/kg i.v.) reduced the inhibitory phase. The selective NK-2 receptor agonist [beta-Ala8] neurokinin A(4-10) caused LOS excitation only. These data indicate that intra-oesophageal acid causes substance P release from extrinsic afferent nerve endings which activates local inhibitory pathways to the LOS via NK-1 receptors.

Review article: factors protecting the oesophagus against acid-mediated injury

Reflux of gastric acid and pepsins into the lower oesophagus causes symptoms such as heartburn and nausea, and tissue injury leading to erosive oesophagitis and stricture formation. This article reviews the mechanisms involved in protecting the oesophagus against acid-mediated injury, including the role of the lower oesophageal sphincter, secondary oesophageal peristalsis and swallowed saliva. The oesophageal mucosa has inherent abilities to resist acid damage, and recent data from three laboratories suggest a secretory function with local production of bicarbonate and mucus responsive to local acidification. The evidence for these putative oesophageal defence mechanisms is discussed.

Effect of different coffees on esophageal acid contact time and symptoms in coffee-sensitive subjects

The purpose of this study was to correlate the effects of different coffees on esophageal acid contact, heartburn, and regurgitation in patients with coffee-sensitivity. Twenty volunteers with coffee-sensitivity were studied in a double-blind, 3 period, crossover study examining the effect of three regular (caffeinated) coffees (a coffee from the USA--"A"; a "treated" coffee from Europe--"B"; and an "untreated" coffee from Europe--"C") before and after a high-fat test meal. The median acid contact times for coffees A, B, and C were 6.5%, 9%, and 10.5%, respectively (A vs. C, p = 0.005). Significantly fewer patients reported any symptoms with coffee A compared with coffee C (p < 0.05). Symptoms were usually more frequent and severe after the test meal. There was a trend toward fewer and less severe symptoms with the treated coffee (B) compared with its untreated counterpart (C). Our conclusions are as follows: (a) Different coffees induce variations in gastroesophageal reflux in coffee-sensitive individuals. (b) Coffee can be treated in a manner which decreases heartburn symptoms by 75% while decreasing acid contact by only 14%. (c) Gastroesophageal reflux and symptoms of coffee sensitivity increase with the concomitant ingestion of food. (d) Symptoms of dyspepsia appear to be influenced by variations in both the coffee itself and characteristics of susceptible individuals. (e) Although gastroesophageal reflux is important in the genesis of coffee-sensitivity, there must be other factors which act in concert with reflux to produce symptoms of coffee-sensitivity.