Lower Esophageal Sphincter Contraction Research Articles

Group I secreted PLA2 and arachidonic acid metabolites in the maintenance of cat LES tone.

Spontaneous tone of in vitro lower esophageal sphincter (LES) circular muscle is associated with elevated levels of arachidonic acid (AA), PGF(2alpha), and increased [35S]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to Gq-, Gi3-, and G(i1/i2)-like G proteins. Tone and AA levels were reduced by inhibitors of a pancreatic-like (group I) secreted phospholipase A2 (sPLA2), by the cyclooxygenase inhibitor indomethacin, and by the thromboxane A2 antagonist SQ-29548. In addition, pertussis toxin (PTX) reduced LES tone, confirming a role of PTX-sensitive G proteins in maintenance of LES tone. PGF(2alpha) contracted LES smooth muscle (strips and cells) and increased [35S]GTPgammaS binding to Gq and Gi3 in solubilized LES circular muscle membranes. PGF(2alpha)-induced contraction of LES permeable muscle cells was inhibited by Gq and Gi3 but not by G(i1/i2) and Go antibodies. The thromboxane A2 analog U-46619 contracted LES smooth muscle and increased Gq binding. U-46619-induced contraction was inhibited by Gq but not by Gi3, G(i1/i2), and Go antibodies. LES tone and [(35)S]GTPgammaS binding were significantly reduced by indomethacin. We conclude that group I sPLA2 may mediate "spontaneous" LES tone by producing AA, which is metabolized to PGF(2alpha) and thromboxane A2. These AA metabolites activate receptors linked to Gi3 and Gq to maintain LES contraction.

Leukotriene D 4–induced contraction of cat esophageal and lower esophageal sphincter circular smooth muscle

Background & Aims: In esophageal circular muscle, acetylcholine activates phosphatidylcholine-specific phospholipases C and D and phospholipase A 2, producing diacylglycerol and arachidonic acid, which cause contraction by interacting synergistically to activate protein kinase C. In a model of acute esophagitis, leukotriene D 4 (LTD 4) contributes to acetylcholine-induced contraction. We examined intracellular signaling in LTD 4-induced contraction. Methods: Esophageal and lower esophageal sphincter (LES) cells, isolated by enzymatic digestion, were contracted by LTD 4 in the absence or presence of inhibitors. Permeabilization by saponin allowed use of G-protein antibodies and heparin. Results: Esophageal contraction was inhibited by pertussis toxin, G i3 antibodies, D609 (phosphatidylcholine-specific phospholipase C inhibitor), propranolol (phospholipase D pathway inhibitor), and chelerythrine (protein kinase C antagonist) but not W7 (calmodulin antagonist). LES contraction was unaffected by pertussis toxin. It was inhibited by G q antibodies, U-73122 (phosphatidylinositol-specific phospholipase C inhibitor), heparin (inositol 1,4,5-trisphosphate inhibitor), and W7 and reduced by D609. Conclusions: In the esophagus, LTD 4 activates a protein kinase C–dependent pathway through pertussis toxin–sensitive G i3 proteins and phosphatidylcholine-specific phospholipase. In the LES, LTD 4 activates a calmodulin-dependent pathway through pertussis toxin–insensitive G q proteins and phosphatidylinositol-specific phospholipase C. The intracellular pathways activated by LTD 4 in the esophagus and the LES are similar to those activated by acetylcholine and other agonists. GASTROENTEROLOGY 1998;115:919-928

Signal Transduction Pathways in Esophageal and Lower Esophageal Sphincter Circular Muscle

Esophageal reflux is a common condition that affects children and 1 in 10 adults, and if untreated may result in chronic esophagitis, aspiration pneumonia, esophageal strictures, and Barrett’s esophagus, a premalignant condition. Although esophagitis is a multifactorial disease that may depend on transient lower esophageal sphincter (LES) relaxation, speed of esophageal clearance, mucosal resistance, and other factors, impairment of LES pressure is a common finding in patients complaining of chronic heartburn. Our data suggest that esophageal and LES circular muscle utilize distinct Ca 2+ sources, phospholipid pools, and signal transduction pathways to contract in response to acetylcholine (ACh): (1) In esophageal muscle ACh-induced contraction requires influx of extracellular Ca 2+ and may be linked to phosphatidylcholine metabolism, production of diacylglycerol (DAG) and arachidonic acid, and activation of a protein kinase C (PKC)-dependent pathway. (2) In LES muscle ACh-induced contraction utilizes intracellular Ca 2+ release arising from metabolism of phosphatidylinositol (PI), and a calmodulin-myosin light chain kinase-dependent pathway. Resting LES tone, on the other hand, may be due to relatively low basal PI hydrolysis resulting in submaximal levels of inositol triphosphate (IP 3)-induced calcium release and interaction with DAG to activate PKC. (3) After induction of experimental esophagitis, basal levels of PI hydrolysis and intracellular calcium stores are substantially reduced, resulting in a reduction of resting tone. In addition the signal transduction pathway responsible for LES contraction in response to ACh changes from one that depends on IP 3 production, calcium release, and calmodulin activation to one that relies on influx of extracellular calcium and activation of PKC.

Superior laryngeal nerve stimulation in the cat: effect on oropharyngeal swallowing, oesophageal motility and lower oesophageal sphincter activity.

Superior laryngeal nerve (SLN) stimulation can activate the brainstem swallowing mechanism to produce a complete swallowing sequence consisting of oropharyngeal, oesophageal and lower oesophageal sphincter (LOS) components. However, little is known of the effect of SLN stimulation (peripheral-sensory input from the pharynx) on the characteristics of oesophageal motor activity, especially in the smooth muscle portion. The present study examined the effect of varying stimulus train length and frequency on each of the three components of the reflex. Acute studies were performed in urethane anaesthetized cats. Oesophageal motility was monitored using conventional manometric techniques, and oropharyngeal swallowing by the mylohyoid electromyogram. SLN stimulus train length (1-10 sec) and frequency (5-30 Hz) were varied independently. Increased train length or frequency resulted in (1) an increase in oropharyngeal swallowing and incidence of the complete swallowing response, (2) an increase in latency to onset of the oesophageal peristaltic wave, (3) reduction of the amplitude of the evoked peristaltic contraction in the smooth muscle portion, without altering its velocity, (4) increased LOS relaxation, and increased LOS after-contraction. The LOS contraction was abolished by atropine (100 micrograms kg-1). Therefore, increased SLN stimulation not only results in excitation of the central swallowing program and the oropharyngeal stage of swallowing, but has major effects on the oesophageal and LOS stages of swallowing. Afferent SLN stimuli can impact on the control mechanisms for each stage, to inhibit or excite the stages in different ways.

Relationship between nitric oxide and non-adrenergic non-cholinergic inhibitory nerves in human lower esophageal sphincter.

Nitric oxide (NO) has recently been shown to be a neurotransmitter in the non-adrenergic non-cholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the the role of NO in the human lower esophageal sphincter (LES), enteric nerve responses in lower esophageal tissue specimens obtained from patients with esophageal cancer (n = 7) and patients with gastric cancer (n = 6) were investigated. A mechanographic technique was used to evaluate in vitro LES muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, including NG-nitro-L-arginine (L-NNA) and L-arginine. Findings were: (1) Cholinergic nerves were those mainly involved in the regulation of enteric- nerve responses to EFS in the steady state, and NANC inhibitory nerves acted on the LES; (2) L-NNA concentration-dependently inhibited the relaxation in response to EFS in the LES; and (3) this inhibitory effect in the LES was reversed by L-arginine. These findings suggest that cholinergic and NANC inhibitory nerves play important roles in regulating contraction and relaxation of the human LES, and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of the human LES.

Quantification of the oesophageal peristaltic reflex in man.

The peristaltic reflex represents the basis of peristalsis and has two components, ascending contraction above and descending relaxation below the site of distension. Studies of the two components of the reflex in the human oesophagus performed by concurrent monitoring of oesophageal body and lower oesophageal sphincter (LOS) motility are lacking. We investigated the peristaltic reflex in eight healthy volunteers (aged 19-25 years; five male, three female) by two series of eight graded (3-10 mL) balloon distensions performed 11 cm above the LOS, monitoring motor activity in the oesophageal body both above and below the balloon and in the LOS (sleeve sensor). During balloon distension both ascending contraction, as assessed by contractile activity above the balloon, and descending relaxation, as assessed by LOS relaxation, increased linearly with increasing inflation volumes (r = 0.6 and r = 0.8, respectively, both P < 0.0001). The threshold for descending relaxation was lower than that for ascending contraction. The contractile response of the body below the balloon was always lower than above the balloon and occurred with a higher (P < 0.05) frequency at 6 and 7 mL compared to 3, 4 and 10 mL. After balloon deflation an oesophageal contraction, usually accompanied by an LOS contraction, occurred with increasing frequency as the balloon volume increased. Our experimental model allows detailed assessment of the two components of the peristaltic reflex in the human oesophagus in vivo and should prove useful in future studies on the physiology and pathophysiology of this reflex.

Effects of nitric oxide synthase blockade on esophageal peristalsis and the lower esophageal sphincter in the cat.

The present study explores the role of nitric oxide (NO) in control of esophageal peristalsis and lower esophageal sphincter (LES) function in the cat. Studies were performed on 20 ketamine-anesthetized cats with manometric recording at the LES, 0, 2, 4, and 6 cm above the LES (smooth muscle section), and 12 and (or) 14 cm above the LES (striated muscle section). L-Ng-Nitro-arginine (L-NNA, 10(-6)-10(-4) mol/kg) was given intravenously, and the effects on swallow-induced esophageal peristalsis were assessed. (i) L-NNA increased the velocity of swallow-induced peristalsis in the smooth muscle esophagus; the effect was dose dependent, more prominent distally, and completely reversed by L-arginine (10(-3) mol/kg). (ii) L-NNA decreased the amplitude of peristaltic contraction in the very distal esophagus; the decrease also was dose dependent but not returned to normal by L-arginine. (iii) L-NNA inhibited LES relaxation (reversed by L-arginine) and decreased the LES "after-contraction" amplitude (unaffected by L-arginine). (iv) L-NNA was associated with the appearance of repetitive contractions. Basal LES tone was unaffected by L-NNA. In conclusion, NO is an important mediator for the timing of peristalsis in the distal smooth muscle esophagus and for LES relaxation in the cat, a species whose contraction amplitude is largely determined by cholinergic excitation. The role of NO in controlling esophageal body and LES contraction amplitude, and in preventing repetitive contractions, requires further study.

Different neurotransmitter systems are involved in the development of esophageal achalasia

Clinical and pharmacological evidence suggests that several neurotransmitters are involved in the control of the esophageal motilility; in fact, besides the well known cholinergic and sympathetic innervation, Vasoactive Intestinal Polypeptide (VIP)-containing fibers as well as dopamine (DA)-containing nerve endings have been identified within the esophageal wall. Lower Esophageal Sphincter (LES) achalasia is a neuromuscular disorder characterized by the absence of peristalsis in the body of the esophagus and by the failure of the LES to relax in response to swallowing. Stimulation of both VIP receptors and D-2 DA receptors induce a decrease in LES pressure, while D-1 receptors mediate LES contractions. In the present study we show that both VIP and DA system is disregulated in LES achalasia. In particular, this disease is associated not only with the lack of VIP nerves in the LES, but also with a failure in the responsiveness of postsynaptic receptors to VIP stimulation. Furthermore, we demonstrate a selective functional loss of the D-2 DA receptor component, without changes in the D-1 DA receptor mediated responses.

Localization and inhibitory actions of galanin at the feline lower esophageal sphincter.

Intrinsic reflexes of the lower esophageal sphincter (LES) are mediated by specific arrangements of excitatory and inhibitory nerves. We have previously described an excitatory reflex at the feline LES mediated by a bombesin-like peptide (BN) which causes release of substance P (SP) to directly contract the LES. Galanin is a neurotransmitter in the enteric nervous system which colocalizes in neurons containing vasoactive intestinal peptide (VIP). The aims of this study were to determine: (1) the distribution of galanin at the feline LES; (2) the effect of galanin on basal LES tone; (3) the effect of galanin on agonist-induced LES contractions by BN, SP and bethanechol; and (4) the effect of galanin on LES relaxation induced by esophageal distension and exogenous VIP. Galanin-like immunoreactivity (galanin-LI) was localized in neurons that were widely distributed throughout the LES and adjacent organs. Galanin-LI was most abundant in the circular muscle, muscularis mucosa and myenteric plexus of the LES. In anesthetized cats, intra-arterial galanin had no effect on basal LES pressure in a dose range of 10(-11) to 10(-6) g/kg. Galanin (5.10(-7) g/kg) reduced the LES contractile response to SP by 65 +/- 8% (P = 0.0001). This galanin-mediated inhibition of SP was not blocked by tetrodotoxin. Galanin similarly decreased the LES contractile response to BN (63 +/- 7%, P = 0.005) and bethanechol (55 +/- 17%, P = 0.012). Galanin had no effect on the LES relaxation induced by esophageal distension or exogenous VIP. We conclude: (1) galanin-LI is present in neurons at the feline LES; (2) galanin has no effect on basal sphincter tone, but inhibits contractions of the LES by both direct and indirect agonists; and (3) galanin does not effect the LES relaxation induced by esophageal distension or VIP.

Experimental and clinical studies on lower esophageal sphincter motor function with special reference to the influence of vagal denervation

Dysmotility of lower esophageal sphincter (LES) is common following gastric surgery. This may result in gastroesophageal reflux which frequently seen following gastric surgery. The aim of this study was to determine the effect of various surgical procedures on esophagogastric motility in dog and human. Esophago-gastric motility was investigated by strain gauge transducers during fasted and fed state in conscious dogs. Motility recordings were performed in three groups of dogs; 1) control dogs, 2) with truncal vagotomized dogs (TV), 3) with selective proximal vagotomized dogs (SPV). In human, manometric recordings were performed before and after gastric surgery (SPV or distal partial gastrectomy). In control animals, lower esophagus and LES contracted simultaneously with each contractions of the stomach during interdigestive motor contractions in fasted state. In fed state, LES showed tonic contractions, while gastric body showed receptive relaxation. These motility pattern of LES was considered to prevent gastroesophageal reflux in both fasted and fed states. These coordinated LES contractions disappeared following SPV or TV. In human, the amplitude and velocity of esophageal propagating contractions deceased after SPV or distal partial gastrectomy. In conclusion, gastric surgeries such as SPV, TV and/or distal partial gastrectomy caused LES dysmotility. These phenomena explain frequent gastroesophageal reflux following gastric surgery. Supplementation of anti-reflux procedure for gastric surgery should be required in the prevention of gastroesophageal reflux following gastric surgery.

Opposing roles for D-1 and D-2 dopamine receptors in the regulation of lower esophageal sphincter motility in the rat

In the present study we have identified biochemically DA receptors in rat Lower Esophageal Sphincter (LES) and have identified their role in the control of the sphincter motility. Dopamine (DA) both stimulated and inhibited cyclic AMP formation in rat LES; the pharmacological characterization of these effects indicated that they were mediated by D-1 and D-2 receptors, respectively. The results obtained with LES helical strips showed that DA plays both inhibitory and stimulatory effects on the sphincter function; the pharmacological characterization with selective D-1 and D-2 agonists and antagonists strongly suggested that D-1 receptors are involved in LES contraction, while D-2 receptors mediate the relaxation of the sphincter. The same results were obtained by measuring intraluminal LES pressure in anesthetized rats. The selective D-1 agonist fenoldopam (40 μg/kg, i.v.) increased the LES pressure; on the other hand bromocriptine (10 μg/kg, i.v.), which preferentially interacts with D-2 receptors, induced a decrease of the resting LES pressure.

Acute experimental esophagitis impairs signal transduction in cat lower esophageal sphincter circular muscle

It has been previously shown that induction of experimental esophagitis in the cat by esophageal perfusion for 30 minutes with 0.1N HCl for 4 consecutive days results in a significant reduction of in vivo lower esophageal sphincter (LES) resting pressure and in vitro spontaneous tone without affecting esophageal response to KCl. It has also been shown that basal LES tone and LES contraction in response to acetylcholine depend on the release of calcium from intercellular stores, whereas esophageal contraction is mediated by extracellular calcium. The present report shows that esophageal acid perfusion impairs the transduction pathway mediating lower esophageal sphincter contraction in response to acetylcholine through release of intracellular calcium because LES strips and single cells no longer contract in response to acetylcholine if calcium is removed from the physiologic salt solution. This suggests that either the intracellular calcium stores or the release mechanisms that mediate maintenance of tone and contraction in response to acetylcholine may be damaged. However, the acid perfusion has no effect on the acetylcholine response in the esophagus, which is mediated by the influx of extracellular calcium. In the LES circular muscle, the injury results in reduced levels of inositol phosphates without affecting resting levels of 5′-cyclic adenosine monophosphate or 5′-cyclic guanosine monophosphate. The reduced levels of 1,4,5-inositol trisphosphate are consistent with impairment in the mechanisms responsible for release of intracellular calcium, although concurrent damage to calcium stores may also occur.

Intracellular pathways for contraction in gastroesophageal smooth muscle cells

Intracellular pathways utilized for contraction in response to acetylcholine (ACh), inositol 1,4,5-trisphosphate (IP3), and KCl were examined in isolated circular smooth cells from the esophagus, lower esophageal sphincter (LES), and fundus. In physiological nutrient salt solution (PSS) intact muscle cells isolated from these three tissues responded in a similar dose-dependent manner to ACh. In all tissues the contractile response to ACh was maximal at 30 s. Contraction of smooth muscle cells from LES and fundus did not change after incubation in Ca(2+)-free medium, but contraction of esophageal cells was abolished. KCl-induced contraction of all three cell types was also abolished after incubation in Ca(2+)-free medium. After permeabilization with saponin in cytosolic (low Ca2+) salt solution, muscle cells from LES and fundus contracted in a dose-dependent manner in response to IP3, whereas cells from esophagus did not contract. Contraction of permeabilized LES and fundic cells in response to ACh was the same as that of intact muscle cells. Response to IP3 was more rapid than response to ACh; it reached 85% of maximum by 5 s and peaked at 15 s. Calmodulin antagonists W-7 and CGS 9343B blocked contraction in response to ACh in intact cells from LES and fundus but had no effect on ACh-induced contraction in esophageal cells. These antagonists blocked IP3-induced contraction in permeabilized cells from LES and fundus. KCl-induced contraction in intact cells from all three tissues was not blocked by either W-7 or CGS 9343B. These data suggest that calmodulin antagonists block contraction mediated by release of intracellular Ca2+ induced by ACh or IP3.(ABSTRACT TRUNCATED AT 250 WORDS)

Medical treatment of esophageal achalasia

Calcium channel blockers have been previously shown to decrease lower esophageal sphincter (LES) pressure and improve symptoms in achalasia. We performed a placebo-controlled, double-blind, crossover study to assess the effects of oral nifedipine and verapamil on LES pressure, amplitude of esophageal body contraction, and clinical symptomatology in eight patients with symptomatic achalasia diagnosed by endoscopy, barium swallow, and manometry. Patients were randomized to receive up to 20 mg nifedipine, 160 mg verapamil, or placebo and underwent esophageal manometry before (baseline) and after four weeks on each drug. Diary cards were kept to record and grade symptoms and drug plasma level determinations were correlated with manometric and clinical findings. Both nifedipine and verapamil caused a statistically significant decrease in mean LES pressure, but only nifedipine caused a significant decrease in the amplitude of contractions of the smooth muscle portion of the esophagus. No statistically significant differences in the overall clinical symptomatology were noted with any of the drugs, although some individual improvements in dysphagia and chest pain were noted. We conclude that, despite the reduction in LES pressure and contraction amplitude of the distal esophageal body, oral nifedipine and verapamil do not significantly alter the clinical symptomatology of patients with achalasia.

Tachykinins in the canine gastroesophageal junction

Lower esophageal sphincter (LES) effects produced by the mammalian tachykinins were evaluated in anesthetized dogs. The distribution and content of substance P (SP) and neurokinin A (NKA) in the region of the canine gastroesophageal junction was also studied. SP and NKA stimulated a linear dose-dependent contraction of the LES after intra-arterial administration. Neurokinin B (NKB) failed to stimulate an increase in LES pressure (LESP). SP was characterized by an immediate but short-lived contraction followed by a period of relaxation. NKA stimulated a potent LES contraction that was slow in onset but long-lasting. On an equimolar basis, both SP and NKA were approximately 100 times more potent LES stimulants than bethanechol or phenylephrine. Pretreatment with atropine (muscarinic blockade) or tetrodotoxin (neural blockade) inhibited the effect produced by SP. NKA appeared to stimulate LES contraction independent of neural or cholinergic mechanisms. Radioimmunoassay revealed a regional variation in tachykinin content in the gastroesophageal junction. Ganglia, cell bodies, nerve fascicles, and neurites stained specifically for both SP and NKA. The variable effects, potencies, and mechanisms of action observed in this study suggest the presence of specific tachykinin receptor subtypes in the gastroesophageal junction. Both SP and NKA were found to have a broad neural distribution in this region. These findings suggest that the tachykinins may play an important role in neuroregulation of LES smooth muscle.

Neural Contribution to Interdigestive Lower Esophageal Sphincter Pressure Phenomena in the Conscious Opossum

The genesis of lower esophageal sphincter (LES) pressure in anesthetized opossums is a myogenic phenomenon without excitatory neural input. The mechanism responsible for generating phasic LES pressure phenomena in unanesthetized opossums, however, is not established. In this study, we evaluated the effects of potential pharmacological antagonists on LES pressure phenomena in unanesthetized opossums. We also compared LES responses to pharmacological excitatory agonists in anesthetized and unanesthetized animals. In awake animals the LES exhibited substantial tone as well as characteristic phasic activity. The tonic, or basal, LES pressure did not change during cycling of the migratory motor complex (MMC). However, atropine, 4‐diphenylacetoxy‐N‐methylpiperidine methiodide, and hexamethonium abolished the phasic, MMC‐related LES contractions while having no effect on basal pressure. Pirenzepine, prazosin, propranolol, pyrdamine, naloxone, and haloperidol did not affect either phasic or tonic LES pressure phenomena. Anesthesia substantially reduced the excitatory LES response to motilin but not to bethanechol, cholecystokinin‐octapeptide, pentagastrin, or phenylephrine. The results suggest that phasic LES contractions related to the MMC cycle are mediated by postganglionic cholinergic nerves with nicotinic ganglionic transmission. Basal LES tone, however, is maintained by a myogenic phenomenon. Anesthesia reduces excitatory LES responses induced by motilin, which acts via excitatory nerves, but has no effect on excitatory responses induced by agents that act mainly or exclusively on LES smooth muscle.

Somatostatin selectively inhibits excitatory contractile pathways of the feline lower esophageal sphincter

Intrinsic reflexes of the feline lower esophageal sphincter (LES) have been shown to be mediated by specific arrangements of excitatory peptidergic interneurons. Inhibition of intrinsic reflexes may also be mediated by neuropeptides. The specific aims of this study were: (1) to examine the effect of somatostatin (SOM) and vasoactive intestinal peptide (VIP) on basal LES tone, and (2) to determine if these transmitters exert selective inhibitory effects on excitatory contractile pathways. Intraluminal pressures were recorded from the LES, esophagus and fundus by a fixed perfused catheter assembly in anesthetized cats. Peptides were administered via the left gastric artery. SOM had no effect on basal LES pressure with doses ranging from 10 −9 to 10 −5 g/kg. VIP induced a dose-dependent inhibition of basal LES pressure. The maximal effective dose of VIP, 10 −6 g/kg, completely inhibited basal LES pressure ( 34.7 ± 6.8 to 1.0 ± 0.6 mmHg , P < 0.001). We have previously shown that bombesin (BN) but not substance P (SP) or bethanechol contracts the LES via tetrodotoxin-sensitive pathways. BN at the D 50 (5·10 −8 g/kg) increased LES pressure by 32.1 ± 3.6 mmHg . SOM (10 −5 g/kg) decreased this BN response to 19.2 ± 5.0 mmHg , P < 0.05. In contrast, while the D 50 of SP (5·10 −8 g/kg) gave a similar increase in LES pressure, 28.8 ± 5.1 mmHg , this effect was not altered by SOM ( 23.8 ± 6.7 mmHg , P > 0.10). SOM also had no effect on bethanechol-induced LES contractions ( P > 0.10). VIP (10 −6 g/kg) totally inhibited the LES response to the D 50 of BN, SP, and bethanechol. A submaximal dose of VIP (10 −7 g/kg) partially inhibited the contractile response of all three. Conclusions: (1) VIP, but not SOM, inhibits basal LES tone. (2) SOM selectively inhibits BN but not SP- or bethanechol-induced LES contraction. (3) VIP inhibits BN, SP and bethanechol-induced LES contractions. These studies suggest that somatostatin can selectively inhibit excitatory interneurons at the LES.

Calcitonin gene-related peptide: a sensory and motor neurotransmitter in the feline lower esophageal sphincter

The effect of calcitonin gene-related peptide (CGRP) on the feline lower esophageal sphincter (LES) was determined and correlated with its anatomic distribution as determined by immunohistochemistry. Intraluminal pressures of the esophagus and LES were recorded in anesthetized cats. In separate cats, gastroesophageal junctions were removed after locating the LES manometrically and stained for CGRP-like immunoreactivity (LI) and substance P-LI (SP-LI) by indirect immunohistochemistry. CGRP-LI in the LES was most prominent in large nerve fascicles between the circular and longitudinal muscle layers and only rarely seen in nerve fibers within the circular muscle. The myenteric plexus contained numerous CGRP-LI nerve fibers but cell bodies were not seen. Many CGRP-LI nerve fibers in the myenteric plexus and occasional varicose nerves in the circular muscle demonstrated colocalization with SP-LI. Colocalization of CGRP-LI with SP-LI was also seen in the perivascular nerves of the submucosal and intramural blood vessels and in varicose fibers in the lamina propria of the gastric fundic mucosa. In the esophagus, CGRP-LI nerves extended through the muscularis mucosa and penetrated the squamous epithelium to the lumen. CGRP, given intra-arterially, caused a dose-dependent fall in basal LES pressure, with a threshold dose of 10 −8 g/kg (2.63 pmol/kg). At the maximal effective dose, 5 × 10 −6 g/kg (1.31 × 10 3 pmol/kg), CGRP produced 61.0 ± 6.0% decrease in basal LES pressure. At this dose, mean systemic blood pressure fell by 40.9 ± 7.8%. The LES relaxation induced by a submaximal dose of CGRP (10 −6 g/kg, 262.7 pmol/kg), 50.3 ± 3.2% relaxation was partially inhibited by tetrodotoxin (26.9 ± 10.8% relaxation, P < 0.025). The inhibitory effect of CGRP was not affected by cervical vagotomy, hexamethonium, atropine, propranolol, or naloxone. The LES contractile response to the D 50 of SP (5 × 10 −8 g/kg, 37.1 pmol/kg) was not altered by CGRP 10 −8 or 10 −6 g/kg and the CGRP relaxation effect was not altered by the threshold dose of substance P (5 × 10 −9 g/kg, 3.71 pmol/kg). Conclusions: (1) CGRP-LI is present at the feline LES and is primarily seen in large nerve fascicles which pass from the intermuscular plane and through the circular muscle layer to the submucosa and in mucosal nerves. (2) CGRP colocalizes with SP-LI in some varicose nerve fibers of the circular muscle of the esophagus, LES and fundus, in perivascular nerves of the submucosal and intramucosal blood vessels, and in nerves of the lamina propria of the gastric fundus. (3) The luminal penetration of CGRP-LI nerves in the squamous mucosa of the esophagus suggests a sensory function for some CGRP-LI nerves. (4) CGRP exerts a dose-dependent inhibitory effect at the LES by both a neural and a direct smooth muscle effect. (5) Despite colocalization in nerve fibers in the muscularis propria at the LES, CGRP exerts no influence on SP-induced LES contractions.

The effect of vagotomy and gastrectomy on the lower esophageal sphincter motility

The motor activity of the canine lower esophageal sphincter (LES) was studied under conscious states by means of the strain gage transducer, and gastroesophageal reflux was investigated after injection of the contrast medium through the silastic tube inserted in gastric fundus by x-ray. The motor activity and function of LES were observed in the dogs with selective proximal vagotomy (SPV), truncal vagotomy (TV) and TV + gastrectomy. Results were summarized as follows; 1. In the postprandial period, so called receptive relaxation was observed in gastric body, and tonic contraction was observed in LES. On the other hand, the occurrence of the LES contraction was consistent with gastric periodic motor activity in the interdigestive state. It was found that such a contractile pattern of LES and gastric body prevented the reflux of gastric juice from stomach to esophagus in the digestive and interdigestive state. 2. In the postprandial period, the tonic contraction of LES was inhibited by the venous injection of atropine sulfate. Mechanisms of digestive contractile activity of LES were mainly regulated by cholinergic nerve. 3. After SPV and TV, the motility of LES and gastric body was disturbed. Namely, receptive relaxation disappeared, and tonic contraction was observed in gastric body, but the relaxation of the LES was found after ingestion. These findings suggested that discordant LES contractiles with the contraction of the gastric body after vagotomy produced a gastroesophageal reflux. 4. After TV + gastrectomy, the synchronous motor activity of the LES, remnant stomach and duodenum disappeared. Namely, it was thought that the reflux esophagitis occurred after gastric surgery with vagotomy and lymphnodes dissection was caused by the duodenal juice reflux to remnant stomach and esophagus.

Contraction mediated by Ca2+ influx in esophageal muscle and by Ca2+ release in the LES.

Single cells and whole tissue specimens were used in this study to determine sources of Ca2+ utilized for contraction of the circular muscle layer of esophagus and lower esophageal sphincter (LES) of the cat. In vitro circular muscle specimens from the cat esophagus respond to electrical stimulation with phasic contractions at the end of the stimulus, whereas the LES spontaneously maintains tonic contraction and relaxes during stimulation. In Ca2+-free buffer, esophageal contractions rapidly decline and disappear within 10 min after the removal of Ca2+, while LES tone is only partially reduced. Similarly, incubation in a solution containing the Ca2+ influx blocker, La3+, abolishes esophageal contraction but only partially decreases LES tone. Conversely, strontium and caffeine substantially reduce LES tone without affecting the amplitude of esophageal contractions. In single muscle cells isolated by enzymatic digestion from the LES and the body of the esophagus, blockade of extracellular Ca2+ influx by methoxyverapamil (D 600) or ethyleneglycol-bis-(beta-aminoethylether) N,N'-tetraacetic acid abolished esophageal contraction in response to acetylcholine without affecting LES cells, and conversely, strontium abolished LES contraction without affecting esophageal cells. These data are consistent with the view that extracellular Ca2+ is required to initiate esophageal phasic contraction, while the LES has the ability to utilize intracellular Ca2+ to maintain resting tone and to contract in response to acetylcholine.