Role of nitric oxide in esophageal peristalsis

A Potential Role of Cholinergic Dysfunction on Impaired Colon Motility in Experimental Intestinal Chagas Disease

Background/Aims

Chagasic megacolon is caused by Trypanosoma cruzi, which promotes in several cases, irreversible segmental colonic dilation. This alteration is the major anatomic-clinical disorder, characterized by the enteric nervous system and muscle wall structural damage. Herein, we investigate how T. cruzi-induced progressive colonic structural changes modulate the colonic contractile pattern activity.

Methods

We developed a murine model of T. cruzi-infection that reproduced long-term modifications of the enlarged colon. We evaluated colonic and total intestinal transit time in animals. The patterns of motor response at several time intervals between the acute and chronic phases were evaluated using the organ bath assays. Enteric motor neurons were stimulated by electric field stimulation. The responses were analyzed in the presence of the nicotinic and muscarinic acetylcholine receptor antagonists. Western blot was performed to evaluate the expression of nicotinic and muscarinic receptors. The neurotransmitter expression was analyzed by real-time polymerase chain reaction.

Results

In the chronic phase of infection, there was decreased intestinal motility associated with decreased amplitude and rhythmicity of intestinal contractility. Pharmacological tests suggested a defective response mediated by acetylcholine receptors. The contractile response induced by acetylcholine was decreased by atropine in the acute phase while the lack of its action in the chronic phase was associated with tissue damage, and decreased expression of choline acetyltransferase, nicotinic subunits of acetylcholine receptors, and neurotransmitters.

Conclusions

T. cruzi-induced damage of smooth muscles was accompanied by motility disorders such as decreased intestinal peristalsis and cholinergic system response impairment. This study allows integration of the natural history of Chagasic megacolon motility disorders and opens new perspectives for the design of effective therapeutic.

On the origin of rhythmic contractile activity of the esophagus in early achalasia, a clinical case study

A patient with early achalasia presented spontaneous strong rhythmic non-propulsive contractions at ~7/min, independent of swallows. Our aim was to evaluate characteristics of the rhythmic contractions, provide data on the structure of pacemaker cells in the esophagus and discuss a potential role for interstitial cells of Cajal (ICC) in the origin of rhythmicity. We hypothesize that intramuscular ICC (ICC-IM) are the primary pacemaker cells. The frequency but not the amplitude of the rhythmic contractions was inhibited by the phosphodiesterase inhibitor drotaverine consistent with cAMP inhibiting pacemaker currents in ICC-IM. The frequency increased by wet swallows but not dry swallows, consistent with stretch causing increase in slow wave frequency in ICC-IM. New studies on archival material showed that ICC-IM were present throughout the human esophageal musculature and were not diminished in early achalasia. Although ICC-IM exhibited a low density, they were connected to PDGFRα-positive fibroblast-like cells with whom they formed a dense gap junction coupled network. Nitrergic innervation of ICC was strongly diminished in early achalasia because of the loss of nitrergic nerves. It therefore appears possibly that ICC-IM function as pacemaker cells in the esophagus and that the network of ICC and PDGFRα-positive cells allows for coupling and propagation of the pacemaker activity. Loss of nitrergic innervation to ICC in achalasia may render them more excitable such that its pacemaker activity is more easily expressed. Loss of propagation in achalasia may be due to loss of contraction-induced aboral nitrergic inhibition.

Examination of the effects of vardenafil on esophageal function using multichannel intraluminal impedance and manometry

Background/Aims

To evaluate the effects of the phosphodiesterase type 5 (PDE5) inhibitor vardenafil on esophageal function, including bolus transit, using multichannel intraluminal impedance and esophageal manometry (MII-EM).

Methods

Sixteen healthy volunteers (15 men) underwent an MII-EM study including 10 liquid swallows and 10 viscous swallows in a seated position after fasting. Then, each subject was asked to ingest 50 mL distilled water or 10 mg vardenafil dissolved in 50 mL water, in a double-blind manner. After 25 minutes, the MII-EM study was repeated.

Results

Eight men received vardenafil and eight subjects received water. Resting and residual lower esophageal sphincter pressures differed significantly only in the vardenafil group (from 18 ± 6.7 to 6.6 ± 5.3 mmHg, P < 0.001 and from 4.9 ± 2.6 to 2.1 ± 3.6 mmHg, P = 0.006, respectively). Mean distal esophageal amplitude decreased significantly only in the vardenafil group (from 86.7 ± 41.6 to 34.0 ± 38.0 mmHg, P < 0.05). Complete bolus transits of liquid and viscous meals decreased significantly only after vardenafil ingestion (from 80.2% ± 13.8% to 49.4% ± 27.9%, P < 0.05 and from 72.8% ± 33.6% to 21.5% ± 29.0%, P = 0.01, respectively).

Conclusions

Vardenafil decreased esophageal bolus transit in the seated position, despite decreased lower esophageal sphincter pressure.

Lower esophageal sphincter relaxation reflex kinetics: effects of peristaltic reflexes and maturation in human premature neonates

We defined the sensory-motor characteristics of the lower esophageal sphincter relaxation (LESR) (stimulus threshold volume, response onset, and relaxation period, relaxation magnitude, nadir) during maturation in human neonates. We hypothesized that LESR kinetics differs during maturation and with peristaltic reflex type. Basal and adaptive esophageal motility testing was performed (N = 20 premature neonates) at 34.7 and 39.1 wk (time 1 and time 2). Effects of midesophageal provocation with graded stimuli (N = 1,267 stimuli, air and liquids) on LESR kinetics during esophagodeglutition response (EDR) and secondary peristalsis (SP) were analyzed by mixed models. Frequency of LESR with basal primary peristalsis were different during maturation (P = 0.03). During adaptive responses with maturation, 1) the frequencies of peristaltic reflexes and LESR were similar; 2) liquid stimuli resulted in a shorter LESR response latency and LESR nadir and greater LESR magnitude (all P < 0.05); 3) media differences were noted with LESR response latency (air vs. liquids, P < 0.02); and 4) infusion flow rate-LESR were different (P < 0.01 for air and liquids). Mechanistically, 1) frequency of LESR was greater during peristaltic reflexes at both times (vs. none, P < 0.0001); 2) LESR response latency, duration, and time to complete LESR were longer with EDR (all P < 0.05, vs. SP at time 2); and 3) graded stimulus volume LESR were different for air and liquids (P < 0.01). In conclusion, sensory-motor characteristics of LESR depend on the mechanosensitive properties of the stimulus (media, volume, flow), type of peristaltic reflex, and postnatal maturation. Maturation modulates an increased recruitment of inhibitory pathways that favor LESR.

Real-time dynamics of nitric oxide shifts within the esophageal wall

BACKGROUND

Currently, indirect evidence suggests that the neurotransmitter nitric oxide (NO) plays a crucial role in the genesis of aboral propagation of esophageal peristalses during swallowing. However, direct evidence in this regard currently is lacking. This study aimed to assess the feasibility of using NO-selective microprobes to detect real-time NO changes within the esophageal wall of North American opossums (Didelphis virginiana) during normal progressive esophageal peristalsis and induced esophageal dysmotility.

METHODS

Six adult opossums of both sexes (mean weight, 2.28 +/- 0.41 kg) were included in the study. All had normal esophageal motility, as documented by water-perfused esophageal manometry. A calibrated carbon fiber NO-selective microelectrode (ISNOP30, ISNOP100) was placed within the smooth muscle portion of the esophageal wall, and changes in NO levels were measured as redox current in pico-amperes (pA) with the Apollo-4000 NO meter. The dynamics of NO in response to reflexive deglutition were assessed during both normal propagative peristalsis and abnormal esophageal contractions induced by intravenous (i.v.) administration of the neural NO synthase inhibitor L-nitro L-arginine methyl ester (L-NAME) and banding of the gastroesophageal junction (GEJ) for 4-weeks.

RESULTS

During normal propagative esophageal peristalsis, a mean change of 2,158.85 +/- 715.93 pA was measured by the NO meter. Intravenous administration of L-NAME and chronic banding of the GEJ induced achalasia-like esophageal contractions. A significantly smaller change in levels of NO was detected within the esophageal wall during dysfunctional motility (331.94 +/- 188.17 pA; p < 0.001) than during normal propagative peristalsis (579 +/- 385 pA; p < 0.001).

CONCLUSION

The results of this study indicate that carbon fiber NO-selective microprobes can successfully measure changes in the concentration of NO, an important inhibitory neurotransmitter, within the esophageal wall and that these preliminary data support the involvement of this crucial neurotransmitter in programming normal propagation of peristaltic waves within the esophagus.

Effects of excitatory and inhibitory neurotransmission on motor patterns of human sigmoid colon in vitro

BACKGROUND AND PURPOSE

To characterize the in vitro motor patterns and the neurotransmitters released by enteric motor neurons (EMNs) in the human sigmoid colon.

EXPERIMENTAL APPROACH

Sigmoid circular strips were studied in organ baths. EMNs were stimulated by electrical field stimulation (EFS) and through nicotinic ACh receptors.

KEY RESULTS

Strips developed weak spontaneous rhythmic contractions (3.67+/-0.49 g, 2.54+/-0.15 min) unaffected by the neurotoxin tetrodotoxin (TTX; 1 microM). EFS induced strong contractions during (on, 56%) or after electrical stimulus (off, 44%), both abolished by TTX. Nicotine (1-100 microM) inhibited spontaneous contractions. Latency of off-contractions and nicotine responses were reduced by N(G)-nitro-L-arginine (1 mM) and blocked after further addition of apamin (1 microM) or the P2Y(1) receptor antagonist MRS 2179 (10 microM) and were unaffected by the P2X antagonist NF279 (10 microM) or alpha-chymotrypsin (10 U mL(-1)). Amplitude of on- and off-contractions was reduced by atropine (1 microM) and the selective NK(2) receptor antagonist Bz-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH(2) (1 microM). MRS 2179 reduced the amplitude of EFS on- and off-contractions without altering direct muscular contractions induced by ACh (1 nM-1 mM) or substance P (1 nM-10 microM).

CONCLUSIONS AND IMPLICATIONS

Latency of EFS-induced off-contractions and inhibition of spontaneous motility by nicotine are caused by stimulation of inhibitory EMNs coreleasing NO and a purine acting at muscular P2Y(1) receptors through apamin-sensitive K(+) channels. EFS-induced on- and off-contractions are caused by stimulation of excitatory EMNs coreleasing ACh and tachykinins acting on muscular muscarinic and NK(2) receptors. Prejunctional P2Y(1) receptors might modulate the activity of excitatory EMNs. P2Y(1) and NK(2) receptors might be therapeutic targets for colonic motor disorders.

Effect of caffeine on lower esophageal sphincter pressure in Thai healthy volunteers

Caffeine affects many aspects of body function including the gastrointestinal system. A single-blinded experimental study was performed to evaluate the effect of caffeine on lower esophageal sphincter (LES) and esophageal peristaltic contractions in healthy Thai adults. The volunteers were six men and six women aged 19-31 years. Subjects drank 100 mL of water. Five wet swallows were performed 30 min after the drink. The basal LES pressure was continuously measured using esophageal manometric technique. They then consumed another 100 mL of water containing caffeine at the dose of 3.5 mg/kg body weight. The swallows and basal LES pressure monitoring were repeated. The results showed no change in basal LES pressure after a water drink while caffeine consumption significantly lowered the pressure at 10, 15, 20 and 25 min. The mean amplitude of contractions and peristaltic velocity were decreased at the distal esophagus at 3 and 8 cm above LES. The mean duration of contraction was decreased at the distal part but increased at the more proximal esophagus. The heart rate, systolic and diastolic blood pressures were increased significantly at 10-20 min after caffeine ingestion. This study indicated that caffeine 3.5 mg/kg affected esophageal function, resulting in a decrease in basal LES pressure and distal esophageal contraction, which is known to promote the reflux of gastric contents up into the esophagus.

Regional differences in cholinergic regulation of potassium current in feline esophageal circular smooth muscle

Potassium channels are important contributors to membrane excitability in smooth muscles. There are regional differences in resting membrane potential and K(+)-channel density along the length of the feline circular smooth muscle esophagus. The aim of this study was to assess responses of K(+)-channel currents to cholinergic (ACh) stimulation along the length of the feline circular smooth muscle esophageal body. Perforated patch-clamp technique assessed K(+)-channel responses to ACh stimulation in isolated smooth muscle cells from the circular muscle layer of the esophageal body at 2 (distal)- and 4-cm (proximal) sites above the lower esophageal sphincter. Western immunoblots assessed ion channel and receptor expression. ACh stimulation produced a transient increase in outward current followed by inhibition of spontaneous transient outward currents. These ACh-induced currents were abolished by blockers of large-conductance Ca(2+)-dependent K(+) channels (BK(Ca)). Distal cells demonstrated a greater peak current density in outward current than cells from the proximal region and a longer-lasting outward current increase. These responses were abolished by atropine and the specific M(3) receptor antagonist 4-DAMP but not the M(1) receptor antagonist pirenzipine or the M(2) receptor antagonist methoctramine. BK(Ca) expression along the smooth muscle esophagus was similar, but M(3) receptor expression was greater in the distal region. Therefore, ACh can differentially activate a potassium channel (BK(Ca)) current along the smooth muscle esophagus. This activation probably occurs through release of intracellular calcium via an M(3) pathway and has the potential to modulate the timing and amplitude of peristaltic contraction along the esophagus.

Nitric oxide modulates peristaltic muscle activity associated with fluid circulation in the sea pansy Renilla koellikeri

Nitric oxide (NO) is a well-known regulator of vascular activities in vertebrates and it has also been implicated as a vasodilatatory agent in a cephalopod. In the sea pansy Renilla koellikeri, an octocorallian representative of the most basal animals with a nervous system, we investigated the role of NO in peristalsis, an activity that moves body fluids through the coelenteron (gastrovascular cavity) of the polyps across the colony. NO donors increased the amplitude of peristaltic contractions and increased tonic contractions in relaxed preparations, but caused a relaxation of basal tension in contracted preparations. The NO synthase (NOS) inhibitors L-NAME (N(ω)-nitro-L-arginine methyl ester) and 7-nitroindazole reduced the amplitude of peristaltic contractions and lowered basal tension. In contrast, aminoguanidine, a specific inhibitor of inducible NOS, increased the amplitude but reduced the rate of peristalsis. Zaprinast, a cGMP-specific phosphodiesterase inhibitor, decreased the amplitude of peristaltic contractions, a decrease that was amplified by dibutyryl cGMP. In contrast,the inhibitor of soluble guanylyl cyclase ODQ(1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one) enhanced peristalsis. Putative NOS-containing neurons, revealed by NADPH-diaphorase activity and citrulline immunohistochemistry, were observed in the basiectoderm at the base of the autozooid polyp tentacles and in a nerve-net around the oral disc. Their neurites ran up the tentacles and down to the polyp body wall, crossing from the ectoderm through the mesoglea and into the endoderm musculature where musculo-epithelial cells were also reactive. These data suggest that two distinct nitrergic pathways, one of which is mediated by cGMP, regulate peristalsis and muscle tone in the sea pansy and that these pathways may involve NOS-containing ectodermal neurons and musculo-epithelial cells.

Ion channel diversity in the feline smooth muscle esophagus

We have characterized ion-channel identity and density differences along the feline smooth muscle esophagus using patch-clamp recording. Current clamp recording revealed that the resting membrane potential (RMP) of esophageal smooth muscle cells (SMC) from the circular layer at 4 cm above the lower esophageal sphincter (EBC4; LES) were more depolarized than at 2 cm above LES. Higher distal Na(+) permeability (but not Cl(-) permeability) contributes to this RMP difference. K(+) channels but not large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels contribute to RMP at both levels, because nonspecific K(+)-channel blockers depolarize all SMC. Depolarization of SMC under voltage clamp revealed that the density of voltage-dependent K(+) channels (K(V)) was greatest at EBC4 due to increased BK(Ca.) Delayed rectifier K(+) channels (K(DR)), compatible with subtype K(V)1.2, were present at both levels. Differences in K(Ca)-to-K(DR) channel ratios were also manifest by predictable shifts in voltage-dependent inactivation at EBC4 when BK(Ca) channels were blocked. We provide the first evidence for regional electrophysiological differences along the esophageal body resulting from SMC ion channel diversity, which could allow for differential muscular responses to innervation and varied muscular contribution to peristaltic contractions along the esophagus.

Regional differences in the response of feline esophageal smooth muscle to stretch and cholinergic stimulation

There are no objective differences in neural elements that explain regional differences in neural influences along the smooth muscle (SM) esophageal body (EB). Regional differences in muscle properties are present in the lower esophageal sphincter (LES). This study examines whether regional differences in SM properties exist along the EB and are reflected in length-tension relationships and responses to cholinergic excitation. Circular SM strips from feline EB at 1 cm (EB1) and 3 cm (EB3) above LES and from clasp and sling muscle bundles of LES were assessed in normal and calcium-free solutions with and without bethanechol stimulation. Neural inhibition was assessed by electrical field stimulation (EFS). EB3 developed significantly higher tension in response to stretch and to bethanechol than did EB1. The relaxation response to EFS in bethanechol-precontracted strips was less in EB3 than in EB1. In LES, clasp developed higher resting tension than sling but less active tension in response to bethanechol. EFS-induced relaxations of sling and clasp tissues precontracted by bethanechol were not different. In calcium-free solution, length-tension differences between EB3 and EB1 persisted, but those of LES clasp and sling were abolished. Therefore, regional myogenic differences exist in feline EB circular SM as well as in LES and may contribute to the nature of esophageal contraction.

Effects of sildenafil on esophageal motility of normal subjects

Sildenafil shows an intense and prolonged inhibitory effect on the smooth muscle cells of corpus cavernosum arterioles by blocking phosphodiesterase type 5 that inactivates the nitric oxide-stimulated cyclic guanosine monophosphate. We investigated if this inhibitory effect is also displayed on smooth muscle cells of the esophagus. In 16 normal subjects (9 men and 7 women, mean age 34 years, range 22-56) esophageal motility was recorded by means of a low-compliance manometric system with side holes for the esophageal body and a sleeve for the lower esophageal sphincter (LES). After a basal period of 60 min, a tablet of sildenafil 50-mg ground and dissolved in water was infused in the stomach in eight subjects (group A) and a placebo tablet in the other eight subjects (group B), randomly and in a double-blind manner; the recording continued for another 60 min. LES tone and postdeglutitive residual pressure, as well as amplitude, propagation velocity, and onset latency of contractions were measured each minute, the values averaged every 5 min, and the mean of the entire basal and postinfusion periods was calculated. The postinfusion values were compared with the basal values in each group and with the corresponding values of the other groups. The percent variations of postinfusion values with respect to basal values were also compared. Sildenafil induced a statistically significant decrease of LES tone, residual pressure, wave amplitude, and propagation velocity and a significant increase of onset latency of pressure waves in comparison with the values of the basal period and placebo. The inhibitory effect reached its maximum 10-15 min after the infusion and lasted about 1 hr. In conclusion, sildenafil markedly inhibits the motor activity of the esophageal musculature by decreasing LES pressure, wave amplitude, and propagation velocity and increasing the onset latency of pressure waves.

Effect of galanin and galanin antagonists on peristalsis in esophageal smooth muscle in the opossum

Galanin, a neuropeptide that is widely distributed in the esophageal nerves, is known to exert a neuromodulatory action in the gut. These studies examined the effect of galanin and galanin antagonists on esophageal peristalsis in anesthetized opossums in vivo. Intraluminal esophageal pressures were recorded at 1, 3, 5, 7, and 9 cm above the lower esophageal sphincter. Esophageal peristaltic contractions were induced by swallow and short- (1-s) and long-train (10-s) vagal stimulation (VS). Galanin (1 nmol/kg) inhibited the amplitude of swallow-induced peristaltic contractions and increased peristaltic velocity by enlarging the latency periods in the upper part of the esophagus and reducing them in the lower part. Galinin nearly abolished esophageal contractions caused by short-train VS at 5 Hz and inhibited the contractions at 10 Hz. Galanin increased latency periods induced by short-train VS with little change in the velocity of peristalsis and reduced the amplitude of both A (cholinergic) and B (noncholinergic) contractions due to long-train VS. However, the decrease in amplitude of B contractions was more marked. Galantide (3 nmol/kg) antagonized the inhibitory action of exogenous galanin on esophageal contractions elicited by short-train VS, but by itself galantide had no significant effect on esophageal contractions. In conclusion, exogenous galanin inhibits the amplitude of swallow-induced peristaltic contractions and converts them into nonperistaltic contractions by inhibiting both the cholinergic and noncholinergic components.

A comparative study of esophageal and anorectal motility in myotonic dystrophy

Myotonic dystrophy may be associated with visceral abnormalities involving smooth muscle, the pathogenesis of which is not clear. Our aim was to evaluate the involvement of smooth and striated muscles at both ends of the gastrointestinal tract. Esophageal and anorectal manometric studies were performed in 13 patients and healthy controls. There was a correlation between: (1) the resting pressure in the upper esophageal sphincter and in the lower anal canal, (2) the amplitude and the coordination of contraction primary waves in the proximal and in the distal esophagus, and (3) the resting pressure in the higher anal canal and in the lower one. These results suggest that both ends of the gastrointestinal tract are disturbed in a similar fashion, both quantitatively and qualitatively and that there is a relationship between smooth and striated visceral muscle involvement in myotonic dystrophy.

Neuromuscular control of esophageal peristalsis

The esophagus is a muscular conduit connecting the pharynx and the stomach. Its function is controlled by an intrinsic nervous system and by input from the central nervous system through the vagus nerve. Peristalsis in its striated muscle is directed by sequential vagal excitation arising in the brain stem, whereas peristalsis in its smooth muscle involves complex interactions among the central and peripheral neural systems and the smooth muscle elements of the esophagus. The peripheral neuronal elements responsible for producing esophageal off-response, relaxation of the lower esophageal sphincter, and hyperpolarization of the circular esophageal muscle cells reside in the myenteric plexus of the esophagus. For many years these nerves were considered nonadrenergic and noncholinergic because the inhibitory neurotransmitter released on their activation was unknown. We now know that nitric oxide or a related compound is that inhibitory neurotransmitter. The primary excitatory neurotransmitter controlling esophageal motor function is acetylcholine. Some disorders of esophageal motor function, including diffuse esophageal spasm and achalasia, may result from defects in or an imbalance between these excitatory and inhibitory neuromuscular systems.

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

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