The role of the L-arginine-nitric oxide pathway in relaxation of the opossum lower oesophageal sphincter

Sildenafil improves clinical signs and radiographic features in dogs with congenital idiopathic megaoesophagus: a randomised controlled trial

We evaluated the efficacy of oral sildenafil citrate in dogs with congenital idiopathic megaoesophagus (CIM). Twenty-one puppies were randomly assigned to two groups (treatment and control). The dogs were given sildenafil oral suspension 1 mg/kg every 12 hours for 14 days or placebo in a masked fashion. Clinical signs (frequency of regurgitation and weight gain) and oesophagrams (relative oesophageal diameter, ROD) were evaluated in order to assess the efficacy of drug treatment, by examiners who were unaware of the study protocol. In addition, a set of in vitro experiments on isolated samples of canine lower oesophageal sphincter (LOS) was performed, and the effects of increasing concentrations of sildenafil on basal tone and electrically-stimulated motility were assessed. Sildenafil administration significantly reduced the number of regurgitation episodes (0.88±1.40 v 2.65±1.56, P<0.0001) and significantly increased weight gain in the treated dogs compared to controls (79.76±28.30 per cent v 53.40±19.30 per cent, P=0.034). ROD values, at the end of the treatment period, were significantly decreased in the sildenafil group, compared to pre-treatment values (0.97±0.19 v 0.24±0.14, P<0.0001), in contrast to control subjects (0.98±0.17 v 1.10±0.25, P=0.480). In accordance with the in vivo findings, sildenafil dose-dependently reduced basal tone and increased electrically-induced relaxation of dog LOS samples. These results suggest that sildenafil citrate helps ameliorate clinical and radiographic signs in dogs with CIM by reducing LOS tone, and could represent a novel therapeutic tool for the treatment of this disease.

The effects of hydrogen sulfide on electrical field stimulation-induced neurogenic contractile responses in isolated rabbit lower esophageal sphincter: Contribution of nitrergic and non-adrenergic non-cholinergic transmission

BACKGROUND

Hydrogen sulfide (H₂S) is a gaseous signaling molecule that, similar to nitric oxide (NO), plays an important role as an inhibitor neurotransmitter in the digestive tract. This study aimed to investigate the effect of H₂S and to identify neurogenic contraction responses dependent on the electrical field stimulation (EFS) in the isolated lower esophageal sphincters of rabbits.

METHODS

An isolated lower esophageal sphincter was placed in an organ bath system and mechanical responses were recorded using a force transducer. The nerve-evoked contractile responses were obtained by EFS. The contractile responses were obtained as biphasic "on" and "off" phases seen at the beginning and end of EFS, respectively.

RESULTS

Sodium hydrogen sulfide (NaHS) reduced the EFS-mediated "off" phase and the EFS-mediated non-adrenergic non-cholinergic (NANC) "off" phase. NaHS reduced the EFS-mediated "on" phase as well. l-Cysteine ​​reduced the EFS-mediated "off" phase and the EFS-mediated NANC "off" phase. l-Propargylglycine (PAG) did not affect the EFS-mediated "off" phase or the EFS-mediated NANC "off" phase. NaHS, l-cysteine, and PAG reduced the EFS-mediated, NO-independent "off" phase. The effect of NaHS in all of the experiments returned in time. Also, NaHS caused significant relaxation of 80-mM KCl-Krebs solution induced-contractions, while l-cysteine ​​and PAG did not cause a significant relaxation.

CONCLUSION

These findings suggest that H₂S has an inhibitory effect on the lower esophageal sphincter muscle. While the effect of H₂S on EFS-mediated responses disappeared in time, the effect of H₂S sustained the KCl-Krebs solution-induced contractions. This shows that H₂S may have an effect on neurotransmission at the nerve terminal.

Dominant role of interstitial cells of Cajal in nitrergic relaxation of murine lower oesophageal sphincter

Oesophageal achalasia is a disease known to result from reduced relaxation of the lower oesophageal sphincter (LES). Nitric oxide (NO) is one of the main inhibitory transmitters. NO-sensitive guanylyl cyclase (NO-GC) acts as the key target of NO and, by the generation of cGMP, mediates nitrergic relaxation in the LES. To date, the exact mechanism of nitrergic LES relaxation is still insufficiently elucidated. To clarify the role of NO-GC in LES relaxation, we used cell-specific knockout (KO) mouse lines for NO-GC. These include mice lacking NO-GC in smooth muscle cells (SMC-GCKO), in interstitial cells of Cajal (ICC-GCKO) and in both SMC/ICC (SMC/ICC-GCKO). We applied oesophageal manometry to study the functionality of LES in vivo. Isometric force studies were performed to monitor LES responsiveness to exogenous NO and electric field stimulation of intrinsic nerves in vitro. Cell-specific expression/deletion of NO-GC was monitored by immunohistochemistry. Swallowing-induced LES relaxation is strongly reduced by deletion of NO-GC in ICC. Basal LES tone is affected by NO-GC deletion in either SMC or ICC. Lack of NO-GC in both cells leads to a complete interruption of NO-induced relaxation and, therefore, to an achalasia-like phenotype similar to that seen in global GCKO mice. Our data indicate that regulation of basal LES tone is based on a dual mechanism mediated by NO-GC in SMC and ICC whereas swallow-induced LES relaxation is mainly regulated by nitrergic mechanisms in ICC.

Effect of nitrite delivered in saliva on postprandial gastro-esophageal function

OBJECTIVE

Acid reflux produces troublesome symptoms (heartburn) and complications including esophagitis, Barrett's esophagus, and adenocarcinoma. Reflux occurs due to excessive and inappropriate relaxation of the lower esophageal sphincter. An important mediator of this is nitric oxide, high concentrations of which are generated within the lumen when swallowed saliva meets gastric acid. Saliva contains nitrite, derived from the enterosalivary recirculation of dietary nitrate, which is reduced to nitric oxide by gastric acid. The aim of this study was to investigate whether salivary nitrite contributes to dysfunction of the lower esophageal sphincter.

MATERIALS AND METHODS

In 20 volunteers, studies of gastro-esophageal function were performed on four separate days, following consumption of a standardized meal, with saliva nitrite concentrations modified differently each day by intra-oral nitrite infusion.

RESULTS

The infusions produced an appropriate range in saliva nitrite concentrations, from below to well above the physiological range. The standardized meal induced expected physiological changes in gastro-esophageal function confirming the recordings were sensitive and robust. Esophageal acid exposure (primary outcome) was similar on each study day. Secondary outcomes, including number and duration of reflux events, rate of transient lower esophageal sphincter relaxations, lower esophageal sphincter pressure and rate of gastric emptying were also unaffected by variations in saliva nitrite concentration.

CONCLUSIONS

Nitrite in swallowed saliva does not modify gastro-esophageal junction function or predispose to gastro-esophageal reflux. The wide range in saliva nitrite concentrations, the sensitivity of the physiological recordings and the number of subjects studied make it very unlikely that an effect has been missed.

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

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

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

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

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

Physiology of normal esophageal motility

The esophagus consists of 2 different parts. In humans, the cervical esophagus is composed of striated muscles and the thoracic esophagus is composed of phasic smooth muscles. The striated muscle esophagus is innervated by the lower motor neurons and peristalsis in this segment is due to sequential activation of the motor neurons in the nucleus ambiguus. Both primary and secondary peristaltic contractions are centrally mediated. The smooth muscle of esophagus is phasic in nature and is innervated by intramural inhibitory (nitric oxide releasing) and excitatory (acetylcholine releasing) neurons that receive inputs from separate sets of preganglionic neurons located in the dorsal motor nucleus of vagus. The primary peristalsis in this segment involves both central and peripheral mechanisms. The primary peristalsis consists of inhibition (called deglutitive inhibition) followed by excitation. The secondary peristalsis is entirely due to peripheral mechanisms and also involves inhibition followed by excitation. The lower esophageal sphincter (LES) is characterized by tonic muscle that is different from the muscle of the esophageal body. The LES, like the esophageal body smooth muscle, is also innervated by the inhibitory and excitatory neurons. The LES maintains tonic closure because of its myogenic property. The LES tone is modulated by the inhibitory and the excitatory nerves. Inhibitory nerves mediate LES relaxation and the excitatory nerves mediate reflex contraction or rebound contraction of the LES. Clinical disorders of esophageal motility can be classified on the basis of disorders of the inhibitory and excitatory innervations and the smooth muscles.

Interstitial cells of Cajal and neuromuscular transmission in the rat lower oesophageal sphincter

The distribution of interstitial cells of Cajal (ICC) and neurotransmission were investigated in lower oesophageal sphincter (LES) circular muscle strips from Sprague-Dawley (SD) rats, Ws/Ws mutant rats and their wild-type (+/+) siblings. Intramuscular c-Kit-positive cells, confirmed to be ICC-IM by electron microscopy, were observed throughout both muscle layers from SD and +/+ rats. In contrast, c-Kit-positive, ultrastructurally typical ICC-IM were absent in Ws/Ws. LES strips from Ws/Ws rats showed increased spontaneous contractile activity. Strips from SD and +/+ rats, responded to electrical neuronal stimulation with a relaxation that was in part L-NNA and in part apamin sensitive, followed by a contraction which was decreased by atropine. In Ws/Ws rats, similar to +/+ rats, neurally mediated relaxation was L-NNA and apamin sensitive and the contraction was decreased by atropine. We conclude that in the rat LES, relaxation is mediated by NO and an apamin-sensitive mediator, and contraction primarily by acetylcholine. Despite the absence of c-Kit-positive ICC, nerve-muscle interaction can be accomplished likely by diffusion of neurotransmitters to the smooth muscle cells. The lack of c-Kit-positive ICC is related to an increase in the basal tone and spontaneous contractile activity. The presence of fibroblast-like ICC in Ws/Ws rats might represent immature ICC whose possible functions need further investigation.

Achalasia: physiology and etiopathogenesis

Achalasia is a disorder of esophageal motility that has been well documented for over 300 years. Despite this, the initiating factor or factors and the underlying mechanisms leading to the characteristic features of achalasia, the absence of distal esophageal peristalsis and abnormal lower esophageal sphincter relaxation, are still not well understood. Recent work has shed light on changes in neurotransmission and cell signaling in the lower esophagus and lower esophageal sphincter that lead to achalasia. A number of recent reviews have thoroughly discussed diagnostic and therapeutic modalities and the reader is referred to these for in-depth review of these topics. The focus of this review will be on our current understanding of the physiology of esophageal peristalsis and lower esophageal sphincter function as it relates to achalasia and on available evidence for etiology and proposed pathophysiologic mechanisms.

Peripheral N-methyl-D-aspartate receptors modulate nonadrenergic noncholinergic lower esophageal sphincter relaxation in rabbits

We investigated the role of peripheral N-methyl-D-aspartate (NMDA) receptors in the myenteric plexus in mediating nonadrenergic noncholinergic (NANC) nitrergic relaxation of the lower esophageal sphincter (LES). Isometric contraction of LES strips from Japanese White rabbits was measured. NANC relaxation was induced by KCl (30 mM) in the presence of atropine and guanethidine. The concentration of 3',5'-cyclic guanosine monophosphate (cGMP) was measured using a radioimmunoassay. The muscle strips were exposed to diethyldithiocarbamic acid (DETCA; 3 mM) to inactivate Cu/Zn superoxide dismutase. MK801 (5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine) inhibited NANC relaxation in a concentration-dependent manner (EC50 = 1.5 x 10(-5) M), accompanied by a decrease in cGMP production. NMDA induced a concentration-dependent relaxation, which was antagonized by MK801. NMDA stimulated cGMP production, which was inhibited by N(G)-nitro-L-arginine. Superoxide dismutase (100 U/mL) shifted the concentration-response relationship of MK801-mediated inhibition of NANC relaxation to the right (EC50 = 3.4 x 10(-5) M), whereas catalase did not. Treatment with DETCA shifted the concentration-response relationships of pyrogallol-, ketamine- and MK801-mediated inhibition of NANC relaxation to the left. These findings suggest that the peripheral NMDA receptors mediate NANC smooth muscle relaxation, and modulate it, in part, through extracellular production of superoxide anions, thus eliminating the relaxant effect of endogenous nitric oxide.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Nitric Oxide Synthesis Inhibition Attenuates Conditioned Reinstatement of Ethanol-Seeking, but Not the Primary Reinforcing Effects of Ethanol

BACKGROUND

Nitric oxide (NO) signaling has been implicated in regulating aspects of the reinforcing and addictive actions of cocaine. These experiments were designed to examine whether NO-dependent neurotransmission also participates in mediating the addictive actions of another drug of abuse, ethanol, with emphasis on both the primary reinforcing effects of ethanol and the incentive motivational effects of ethanol-related contextual stimuli.

METHODS

Male Wistar rats were operantly trained to orally self-administer 10% (w/v) ethanol in daily 30-min sessions and to associate distinct discriminative stimuli with the availability of ethanol (S+) versus nonreward (S-). Rats were treated with the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 0, 10, or 40 mg/kg intraperitoneally) 30 min before self-administration tests that were conducted after establishment of stable levels of daily ethanol intake and conditioned reinstatement tests that were performed after extinction of ethanol-maintained operant responding.

RESULTS

L-NAME did not alter the primary reinforcing effects of ethanol in self-administration tests. In contrast, L-NAME dose-dependently attenuated the recovery of extinguished responding induced by the ethanol S in the absence of ethanol availability during reinstatement tests.

CONCLUSIONS

These results suggest that the NO system does not play a role in behavior reinforced directly by ethanol. However, the results implicate NO-dependent neurotransmission in alcohol-seeking responses elicited by drug-related contextual stimuli.

Muscarinic modulation of nitrergic neurotransmission in guinea-pig gastric fundus

Muscarinic receptor activation by (4-Hydroxy-2-butynyl)-1-trimethylammonium-m-chlorocarbanilate chloride (McN-A-343) was investigated both on NADPH-d staining and on electrically induced responses in guinea-pig gastric fundus. McN-A-343 (10 micromol L(-1)) significantly increased the optical density of NADPH-d positive neurones, while blockade of nitric oxide synthase with N(omega)-nitro-L-arginine (L-NA) decreased it, suggesting facilitation of nitric oxide (NO) production. Electrical field stimulation (EFS; 2 Hz, 0.2 ms, supramaximal current intensity, 10 s train duration) elicited on-contraction followed by off-relaxation in the circular muscle strips. McN-A-343 (10 micromol L(-1)) transformed the EFS-evoked response from on-contraction into on-relaxation, which was neurogenic, tetrodotoxin-sensitive and hexamethonium-resistant. L-NA partly reduced the EFS-evoked relaxation, revealing two components: a nitrergic and a non-nitrergic one. The effect of McN-A-343 on the amplitude of the EFS-evoked relaxation was not changed by the M(3) receptor antagonist para-fluoro-hexahydro-sila-difenidol hydrochloride, but was significantly enhanced by M(1) receptor blockade with telenzepine. In the presence of telenzepine, the L-NA-dependent nitrergic component of the EFS-induced relaxation predominates. We suggest that cholinergic receptor activation has a dual effect on nitrergic neurotransmission: (i) stimulation of NOS by muscarinic receptor(s) different from M(1) and M(3) subtype, (ii) prejunctional inhibition of NO-mediated relaxation via M(1) receptors. In addition, M(1) receptors may facilitate the non-nitrergic relaxation.

Anorectal motility in patients with achalasia of the esophagus: recognition of an esophago-rectal syndrome

BACKGROUND

During my study of constipation, I encountered patients who had achalasia of the esophagus (AE) as well. The possibility of an existing relationship between the 2 conditions was studied.

METHOD

Investigations to study the anorectal motility in 9 AE patients included: the intestinal transit time, anorectal manometry, rectoanal inhibitory reflex, defecography and electromyography (EMG) of external anal sphincter and levator ani muscle. Anorectal biopsy was done. The study comprised 8 healthy volunteers as controls.

RESULTS

6/9 AE patients had constipation presenting as strainodynia (excessive prolonged straining at stool). Rectocele was present in 4 of them. The 6 constipated patients showed significantly high rectal neck pressure (p < 0.05), absent rectoanal inhibitory reflex and aganglionosis in the anorectal biopsy. The EMG revealed diminished activity in 4 of the 6 constipated patients. The remaining 3 patients with AE had normal anorectal function. Heller's myotomy with Nissen's fundoplication improved the dysphagia, but not the constipation which was, however, relieved after performance of anorectal myectomy.

CONCLUSION

The high incidence of constipation with AE postulates a relationship between the 2 conditions. Both have the same pathologic lesion which is aganglionosis. This study is preliminary and requires further studies on a larger number of patients.

Release of nitric oxide in the central nervous system mediates tonic and phasic contraction of the cat lower oesophageal sphincter

Nitric oxide (NO) in the brainstem is implicated in the control of swallowing and oesophageal peristalsis. This study examines the role of brainstem NO in the maintenance of lower oesophageal sphincter (LOS) tone, relaxation and contraction. In urethane-anaesthetized cats, oesophageal peristalsis and sphincter pressures were continuously monitored. Drugs were administered into the fourth ventricle. Oesophageal peristalsis and sphincter relaxation and contraction were induced by superior laryngeal nerve stimulation or intra-oesophageal balloon distention. Basal sphincter pressure was significantly reduced after the i.c.v. administration of the nitric oxide synthase (NOS) inhibitor, l-Ng-monomethyl arginine. The inhibitor's d-isomer had no significant effect on basal sphincter pressure, while l-arginine partially reversed the effect. The NOS inhibitor had no effect on sphincter relaxation, whereas the contraction of the sphincter following relaxation was significantly inhibited. Central nitric oxide synthase inhibition reduces basal LOS tone and contraction amplitude but has no effect on swallow or balloon distention induced sphincter relaxation. Therefore, central release of NO acts in the pathway to stimulate dorsal motor nucleus of the vagus neurones projecting to excitatory neurones in the sphincter. Inhibition of nitric oxide synthase in the CNS does not prevent relaxation of the LOS, suggesting that other pathways that do not utilize NO are important in the induction of LOS relaxation.

Mexiletine inhibits nonadrenergic noncholinergic lower oesophageal sphincter relaxation in rabbits

Nonadrenergic noncholinergic (NANC) nerves are known to be nitrergic and to have an important role in the regulation of gastrointestinal motility and function. Cardiac antiarrhythmic therapy in humans is accompanied by a high incidence of gastrointestinal side-effects. We investigated the effect of mexiletine, a class Ib antiarrhythmic drug, on NANC lower oesophageal sphincter relaxation. Mexiletine concentration dependently inhibited the NANC relaxation induced by 30 mM KCl (EC(50)=4.4 x 10(-6) M); the production of 3',5'-cyclic guanosine monophosphate (cGMP) after KCl stimulation was concentration dependently decreased. The relaxation induced by the exogenous nitric oxide (NO) donor, diethylamine NONOate (10(-5) M), was not inhibited by mexiletine, and the cGMP production after diethylamine NONOate application was not altered. Mexiletine did not alter the activity of NO synthase. These findings suggest that mexiletine inhibits NANC relaxation via NO-cGMP pathway modulation, possibly by inhibiting myenteric nitrergic neurotransmission in the lower oesophageal sphincter in rabbits.

Treatment of achalasia: the short-term response to botulinum toxin injection seems to be independent of any kind of pretreatment

BACKGROUND

It has been suggested that intrasphincteric injection of botulinum toxin (BTX) may represent an alternative therapy to balloon dilatation in achalasia. The aim of the present study was to test the effectiveness of botulinum toxin injections in achalasia patients, as assessed using lower oesophageal sphincter pressure (LOSP) and symptom scores, and to compare the response in patients with different types of pretreatment (no previous treatment, balloon dilatation, myotomy, BTX injection).

METHODS

Forty patients who presented with symptomatic achalasia were treated with BTX injection (48 injections in 40 patients). Some of the patients had received prior treatment (seven with myotomy, seven with dilatation and eight with BTX). The symptoms were assessed using a global symptom score (0-10), which was evaluated before treatment, 1 week afterwards, and 1 month afterwards. Manometry was also carried out before and after treatment. Three different selections of patients were studied: all patients; untreated patients; and patients with prior BTX, dilatation, or myotomy.

RESULTS

After BTX injection, there was a significant reduction in LOSP (before, 38.2+/-11.3 mmHg; 1 week after, 20.5+/-6.9 mmHg; 1 month after, 17.8+/-6.8 mmHg; P < 0.001). The global symptom score and symptom subscores (dysphagia, regurgitation, chest pain) were significantly decreased after 1 week and 1 month. When the beneficial effects following BTX injection were compared (untreated vs. pretreated), neither changes in LOSP nor beneficial effects on the symptom scores significantly differed. After 6 months, 67.7% of all treated patients were still in symptomatic remission (subgroups: previously untreated patients, 61.5%, n = 26; prior dilatation, 71.4%, n = 7; prior myotomy, 71.4%, n = 7; prior BTX, 73.9%, n = 8).

CONCLUSIONS

BTX injection offers an alternative treatment for achalasia which is safe and can be performed in an outpatient setting. The initial response to BTX, in terms of symptom scores and LOSP, appears to be independent of any prior treatment. A number of patients do not adequately respond to balloon dilatation or myotomy, which are the first-line treatment modalities in achalasia patients. BTX injection can be performed in these patients, and symptomatic benefit can be expected in the same percentages as with BTX injection in untreated patients.

Okadaic acid inhibits relaxant neural transmission in rat gastric fundus in vitro

The aim of the present study was to characterize the influence of the phosphatase type 1 and 2A inhibitor okadaic acid on non-adrenergic, non-cholinergic (NANC) neurotransmission in the rat gastric fundus. Okadaic acid (10-6 M), an inhibitor of protein phosphatases 1 and 2A, did not show any influence on the basal tonus or on a contraction plateau induced by 5-HT (10-7 M) within 30 min of observation. When okadaic acid (10-6 M) was applied 10 min prior to 5-HT (10-7 M), the contraction plateau of serotonin was unchanged. To investigate the inhibitory neurotransmission, the muscle strips were pre-contracted using 5-HT (10-7 M), and inhibitory stimuli were applied at the contraction plateau, which was stable over 30 min. The inhibitory effects of vasoactive intestinal peptide (VIP), nitric oxide (NO) and electrical field stimulation (EFS, 40 V, 0.5 ms, frequencies ranging from 0.5 to 16 Hz) were examined. When okadaic acid (10-6 M) was applied prior to EFS-induced NANC relaxation, significant attenuation of the inhibitory response was demonstrated (16 Hz: control: -92.4 +/- 1.9%; okadaic acid 10-7 M: -60.7 +/- 6.1%; okadaic acid 10-6 M: -25.3 +/- 3.4%; n=11; P < 0.01). By contrast, neither the concentration-dependent inhibitory actions of VIP (10-11-10-8 M) (VIP 10-8 M: -100%; VIP 10-8 M + okadaic acid 10-6 M: -89.9 +/- 8.3%; n=8; n.s) nor that of diethylamine nitric oxide (DEA-NO) (3 x 10-7-10-4 M) (DEA-NO 10-4 M: -95.3 +/- 8.4%; DEA-NO 10-4 M + okadaic acid 10-7 M: -98.3 +/- 6.3%; DEA-NO 10-4 M + okadaic acid 10-6 M: 96.5 +/- 7.6%; n=9; n.s.) on 5-HT induced contraction were altered by pre-incubation with okadaic acid (10-6 M). This is the first report that supports the concept that protein phosphatases 1 and 2A may contribute to the regulation of rat gastric fundus motility. The protein phosphatase inhibitor okadaic acid significantly reduces electrically induced inhibitory NANC responses, while leaving direct muscular effects of the inhibitory NANC neurotransmitters VIP and NO unaffected - suggesting a neural site of action. The potential roles of protein phosphatases on NANC neurotransmission remain to be clarified in detail, as this might offer a new pathway for modulating smooth-muscle function.

Current concepts on pathophysiology, diagnosis and treatment of diffuse oesophageal spasm

Diffuse oesophageal spasm is a functional oesophageal motility disorder of unknown aetiology, which appears to be due to a disturbance of the normal pharmacological timing of propulsive contraction occurring in the oesophageal body after swallowing. The lack of pathophysiological understanding may be due to the fact that there is more than one pathophysiological pathway causing symptoms of diffuse oesophageal spasm. Barium studies, oesophageal scintigraphy and fiberoptic examination can be helpful in finding the correct diagnosis, but manometry is still the gold standard of diagnostic procedures. Similar to other spastic oesophageal motility disorders, pharmacological treatment of diffuse oesophageal spasm includes nitrates, calcium antagonists, anticholinergics and antidepressants with varying beneficial effects. Botulinum toxin, which provides sufficient treatment as measured by symptom score and manometric patterns in patients with achalasia, was recently evaluated for the treatment of diffuse oesophageal spasm in small patient selections with promising results.

Effect of sildenafil, a phosphodiesterase-5 inhibitor, on oesophageal peristalsis and lower oesophageal sphincter function in cats

The propagation of oesophageal peristaltic contractions and lower oesophageal sphincter (LOS) relaxation depends on neural release of nitric oxide (NO) which acts to increase intracellular cGMP. Sildenafil, a phosphodiesterase-5 inhibitor that increases cGMP, reduces basal LOS pressure in patients with achalasia. We investigated the effect of sildenafil on the propagation of oesophageal contractions and LOS relaxation in the cat. Oesophageal manometry was performed in five cats under light sedation. Peristaltic contractions were monitored at 1, 2, 3, 4 and 8 cm proximal to the LOS, at the LOS using a Dent sleeve, and at 3 cm distal to the upper oesophageal sphincter. Swallow-induced oesophageal contractions and LOS relaxation were recorded during 30 min before and 30 min after intravenous administration of sildenafil. Sildenafil reduced the amplitude of oesophageal contractions only in the smooth muscle oesophagus. The latency from swallow to distal oesophageal contractions was significantly delayed. LOS pressure was significantly reduced but the relaxation nadir was not modified by sildenafil. Sildenafil has profound effects on oesophageal motility: it modifies propagation and amplitude of oesophageal contractions and reduces LOS pressure. Slowing down the propagation of contractions in the transitional zone between the striated and smooth muscle can be a useful tool in patients with segmental aperistalsis or intermittent simultaneous contractions, while the effect on the LOS can benefit patients with achalasia.

Role of nitric oxide during swallow-induced esophageal shortening in cats

Swallowing induces esophageal shortening due to contraction of the longitudinal muscle (LM) layer. Experiments in the opossum have shown an excitatory effect of nitric oxide (NO) on esophageal LM strips. We evaluated the role of NO in swallow-induced esophageal shortening and assessed the effect of NO in vitro on feline LM strips. Swallow-induced esophageal shortening was studied before and after NO synthase blockade with L-NAME. In five cats esophageal shortening was measured using two endoscopically affixed mucosal clips. In another five cats LM contraction was measured by a strain gauge sutured on the serosal side at 2 cm above the LES; muscle strips from that region were obtained for in vitro studies. Swallowing induced esophageal shortening of 48.3+/-8.3% and LM contraction of 4.4+/-0.8 g in the control period and 32.1+/-8% and 3.0+/-0.4 g after L-NAME (P < 0.05). Nitric oxide and SNP did not change the basal tone of esophageal LM strips but provoked inhibition of metacholine-induced tonic and phasic activity. Electrical field stimulation induced frequency-dependent contractions that were reduced by atropine without further reduction after L-NAME. In conclusion, the reduction of esophageal shortening after L-NAME during the in vivo experiments suggested an excitatory effect of NO on the feline esophagus. The in vitro experiments, however, showed no contractile effect of NO or SNP on LM strips, but an inhibitory effect on the precontracted tissue. The influence of NO synthase blockade on in vivo esophageal LM shortening might be secondary to its effect on circular muscle contractility.

Inhibition of small conductance K+-channels attenuated melatonin-induced relaxation of serotonin-contracted rat gastric fundus

The aim of this study was to investigate the effects of melatonin on rat gastric fundus smooth muscle. Melatonin (10-4 to10-3 M) had no effect on the basal tone of gastric smooth muscle. After precontraction with carbachol (10-6 M) or serotonin (10-7 M), melatonin caused a concentration dependent inhibitory action. The half maximal effect on serotonin-induced contraction was found with 1.12 beta 0.86 beta 10-5 M of melatonin. Increasing concentrations of melatonin (10-5 to 10-3 M) resulted in a right shift of the serotonin concentration response curve (10-10 to10-5 M). This inhibitory effect of melatonin was partially blocked in the presence of apamin (10-10 to 10-7 M), a specific blocker of the small conductance calcium-dependent potassium channel, but not in the presence of other potassium channel blockers like charybdotoxin (10-8 M), glibenclamide (10-5 M), or tetraethylammonium (ODQ, 10-4 M). The inhibitory effect was not changed in the presence of the neuronal blocker tetrodotoxin (10-6 M), the selective P2-receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (3 × 10-5 M), the nitric-oxide synthase inhibitor N-nitro-L-arginine (3 × 10-4 M), or the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (10-4 M), suggesting that neither the purinergic, nitrergic, nor guanylate cyclase pathways were involved. We further investigated inhibitory responses to electrical field stimulation (EFS) at different frequencies under non-adrenergic, non-cholinergic (NANC) conditions on a serotonin-induced contraction in the presence of melatonin (10-5 to 10-4 M). Melatonin significantly reduced these inhibitory NANC responses in higher (8-32 Hz), but not lower (05-4 Hz), frequencies (16 Hz without melatonin, 103 ± 6.3%; melatonin 10-5 M, 80.4 ± 7.5%; melatonin 10-4 M, 39.1 ± 17.1%). Melatonin had no effect on contractile responses induced by EFS under basal tone. These results demonstrate that the inhibitory effect of melatonin in rat gastric fundus smooth muscle is apamin sensitive, but is not affected by other potassium channel blockers. This suggests that melatonin may be another transmitter candidate for the apamin sensitive responses within the gastrointestinal tract.Key words: melatonin, smooth muscle, apamin, NANC-inhibition, gastric, potassium channels.

Nitric oxide and the gut

Nitric oxide (NO) has been implicated as a modulator of blood flow, motility, electrolyte and water transport, and the function of endothelial cells, platelets, mast cells, and macrophages within the digestive system. In addition, a number of reports have demonstrated that NO possesses potent anti-inflammatory properties, whereas results from an equally impressive number of studies suggest that NO may promote inflammation-induced cell and tissue dysfunction. Consideration of the physiologic chemistry of NO and its interaction with molecular oxygen and/or superoxide may allow us to identify which of the NO-dependent reactions are important in modulating physiologic and pathophysiologic responses in the gut.

Biphasic relaxation of the opossum lower esophageal sphincter: roles of NO., VIP, and CGRP

Vasoactive intestinal polypeptide (VIP) and nitric oxide (NO.) are thought to mediate lower esophageal sphincter (LES) relaxation. Transverse muscle strips from the opossum LES were used to test this hypothesis. Electrical field stimulation (EFS) produced a biphasic LES relaxation: a rapid component during the stimulus was more prominent at lower stimulus frequencies, and a sustained component was more prominent at higher frequencies. N(omega)-nitro-L-arginine and hemoglobin inhibited the rapid component but affected the sustained component less. Exogenous VIP decreased LES tone. A number of purported VIP antagonists blocked neither VIP-induced nor EFS-induced relaxation of the LES. The calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) did not alter EFS-induced LES relaxation. EFS-induced relaxation of opossum LES muscle is biphasic, and the initial, rapid component of the relaxation is mediated primarily by NO. The mediator of the sustained component was not identified.

Innervation of the esophagus in mice that lack MASH1

The striated muscle of the esophagus differs from other striated muscle, because it develops by the transdifferentiation of smooth muscle, and the motor end plates receive a dual innervation from vagal (cholinergic) motor neurons and nitric oxide synthase (NOS)-containing enteric neurons. Mash1-/- mice have no enteric neurons in their esophagus and die within 48 hours of birth without milk in their stomachs (Guillemot et al. [1993] Cell 75:463-476). In this study, the innervation of the esophagus of newborn Mash1-/-, Mash1+/- and wild type mice was examined. There was no difference between Mash1-/-, Mash1+/-, and wild type mice in the transdifferentiation of the muscle and the development of nicotinic receptor clusters. However, there were significantly more cholinergic nerve terminals per motor end plate in Mash1-/- mice than Mash1+/- or wild type mice. Each of the Mash1-/- mice had fewer than 50 NOS neurons per esophagus, compared with approximately 3,000 in wild type mice. Newborn Mash1+/- mice also contained significantly fewer NOS neurons than wild type mice. In Mash1-/- mice, NOS nerve fibers were virtually absent from the external muscle but were present at the myenteric plexus. Unlike that of newborn wild type mice, the lower esophageal sphincter of Mash 1-/- mice lacked NOS nerve fibers; this may explain the absence of milk in the stomach. We conclude that 1) the transdifferentiation of the esophageal muscle and the development of the extrinsic innervation do not require enteric neurons or MASH1, 2) extrinsic NOS neurons only innervate the myenteric plexus.

Neuronal pathways and transmission to the lower esophageal sphincter of the guinea Pig

BACKGROUND & AIMS

The lower esophageal sphincter (LES) normally controls the opening and closing of the gastroesophageal junction to resist gastric reflux but allow swallowing. Neuronal pathways controlling the guinea pig LES were investigated anatomically and physiologically in isolated preparations.

METHODS

Intracellular recording from the LES with focal electrical stimulation and retrograde and anterograde neuronal tracing were used.

RESULTS

Electrical stimulation on the LES evoked inhibitory junction potentials (IJPs), which were reduced by 60% by 100 micromol/L N-nitro-L-arginine and subsequently blocked by 0.5 micromol/L apamin, unmasking excitatory junction potentials, which were abolished by 1 micromol/L hyoscine. Esophageal or vagal stimulation evoked IJPs, which were blocked by 100 micromol/L hexamethonium. Focal stimulation of the upper stomach evoked IJPs at 5-8 of 20 stimulation sites, which were abolished by cutting between the stimulation site and sphincter. Application of 1,1'-didodecyl-3,3,3', 3'-tetramethyl indocarbocyanine perchlorate (DiI) to the gastric sling muscle anterogradely labeled many motor axons in the sling muscle but few in the LES, confirming that the two muscles are separately innervated. DiI on the esophagus labeled nerve fibers, but not cell bodies, in the upper stomach.

CONCLUSIONS

The inhibitory motor neurons of the LES receive inputs from the vagus nerve, esophagus, and upper stomach.

The ontogeny of innervation of the human pylorus

PURPOSE

The aim of this study was to document the vagal innervation and expression of neuropeptides, neuronal nitric oxide synthase (nNOS), and neural cell adhesion molecule (NCAM) in the neuromuscular system of the developing human pylorus.

METHODS

Specimens of human pylorus (n = 54; age range, 8 weeks' gestation to 6 months postnatal) were studied. Vagal innervation was determined by Dil autofluorescence. A wide range of neuropeptides, NCAM, and the neural isoform of NOS were examined by immunohistochemistry.

RESULTS

Vagal innervation was first recognized in the myenteric plexus in the 12-week-old fetus as was vasoactive intestinal polypeptide (VIP) expression. Neuropeptides were present from 8 weeks' gestation and appeared to be expressed progressively from the adventitia toward the mucosa and showed an adultlike profile by 23 weeks' gestation. A craniocaudal pattern of expression was noted for VIP and nNOS. Alpha smooth muscle actin was expressed by muscle fibers of the muscularis propria from 8 weeks and the muscularis mucosae by 14 weeks. All the isoforms of NCAM examined were expressed from 8 weeks in the muscularis propria and by 12 weeks in the submucosa.

CONCLUSION

The expression of the antigens studied correlated with the gestational age and development of the pylorus.

Nonadrenergic-noncholinergic relaxations of isolated circular muscle from South American opossum esophagogastric junction: is nitric oxide the inhibitory mediator?

Nonadrenergic-noncholinergic (NANC) inhibitory nerves are responsible for most of the nerve induced relaxations of gastrointestinal muscle. It has recently been proposed that NANC nerves may release nitric oxide (NO) or a related compound derived from L-arginine. We have recently shown that the South American (SA) opossum is another suitable model to elucidate the mechanism involved in these NANC relaxations. In the present study the effect of NO synthase inhibitors as well as NO inactivators on the NANC-nerve induced relaxations of the circular muscle of the esophagogastric junction (EGJ) of the SA opossum was investigated. It was observed that the NO synthase inhibitors, L-NOARG and L-NAME, caused a concentration-dependent reduction of NANC-nerve induced relaxations which was reversed by L- but not D-arginine. The NO-donors sodium nitroprusside and hydroxilamine as well as NO caused concentration-dependent relaxations of the EGJ circular muscle. In the myenteric plexus of this region, NADPH-diaphorase positive neurons and nerve fibers were observed while in the circular muscle layer only numerous positive fibers were found. The NO inactivators, hydroquinone, pyrogallol and carboxy-PTIO, reduced NO-induced relaxations but failed to affect NANC nerve- and sodium nitroprusside-induced relaxations. Taken together, these findings indicate that NANC nerve induced relaxation of the SA opossum EGJ circular muscle is dependent on neural NO synthase activity and suggest that the neurotransmitter being released is a superoxide resistant molecule, which is unlikely to be the NO radical, or that the activity of NO synthase is required for the release of the actual neurotransmitter rather than for synthesizing the neuromediator.

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.

DMPP causes relaxation of rat distal colon by a purinergic and a nitrergic mechanism

The non-adrenergic relaxation of carbachol precontracted longitudinal muscle of the rat distal colon was investigated. Intrinsic nerves were activated by the nicotinic, ganglionic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP). DMPP at 1 and 4 microM caused a relaxation that was markedly antagonized by the nerve blocker tetrodotoxin (1 microM) or the nicotinic receptor antagonist, hexamethonium (1 mM). The response to DMPP was significantly antagonized by apamin (an inhibitor of ATP-sensitive K+-channels), by reactive blue 2 (a blocker of P2y purinoceptors) and by an inhibitor of nitric oxide (NO)-synthase (N(G)-nitro-L-arginine, L-NNA). The combined treatment with reactive blue 2 and L-NNA reduced the relaxatory response to 1 microM DMPP by 77 +/- 8% and to 4 microM DMPP by 58 +/- 4% of control, but left a residual component. Our results indicate that ATP and NO, together with at least one additional (hitherto unidentified) substance may be inhibitory neurotransmitters in rat distal colon.

Pituitary adenylate cyclase activating polypeptide and nitric oxide synthase are expressed in the rat ciliary ganglion

AIMS

To study the distribution in the rat ciliary ganglion of neurons synthesising and storing the recently discovered neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) and neuronal nitric oxide synthase (NOS), the neuronal marker of the novel gaseous transmitter nitric oxide.

METHODS

Neurons expressing PACAP and neuronal NOS mRNA were identified in the rat ciliary ganglion by in situ hybridisation with radiolabelled oligonucleotide probes. Immunocytochemistry was used to demonstrate immunoreactive neuropeptides and NOS.

RESULTS

Immunocytochemistry demonstrated immunoreactivity for PACAP and NOS in a small number of neuronal cell bodies. In situ hybridisation revealed that NOS and PACAP were expressed in numerous ganglion cell somata. The well established ciliary messengers vasoactive intestinal peptide and neuropeptide Y were found in a large number of neuronal cell bodies.

CONCLUSION

These results demonstrate that PACAP and NOS are synthesised and stored in the ciliary ganglion. These findings further illustrate the mixed nature of the ciliary ganglion and may provide a basis for the understanding of the diverse physiological functions of this ganglion.

The effect of pelvic nerve stimulation on recto-anal motility in the cat

Rectal and anal motility responses to pharmacological manipulation of neuro-transmission and graded efferent electrical pelvic nerve stimulation were investigated in alpha-1-chloralose anaesthetized cats. N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of nitric oxide synthase, did not influence spontaneous rectal and anal motility. No significant change in anal pressure or rectal tone was observed after sectioning the pelvic nerves in animals pretreated with L-NNA. The effect of pelvic nerve stimulation on anal tone was varying and depended upon the intensity of stimulation and the prevailing anal tone. A reduction of anal tone on pelvic nerve stimulation was consistently converted to an increase of anal tone after pretreatment with L-NNA. The rectal response to pelvic nerve stimulation was unchanged by L-NNA. Residual increase of anal tone observed on pelvic nerve stimulation after L-NNA and noradrenergic blockade was partly sensitive to hexamethonium and abolished by atropine. The results suggest that there is no tonic influence on rectal and anal motility via nitric oxide mechanisms. On the other hand, the reduction of anal tone on high intensity pelvic nerve stimulation seemed to be dependent on the release of nitric oxide. An excitatory cholinergic component of the smooth muscle contractility of the feline anal canal, partly sensitive to hexamethonium, was demonstrated to be conveyed in the pelvic nerves.

Nitrergic inhibition of migrating myoelectric complex in the rat is mediated by vasoactive intestinal peptide

The role of vasoactive intestinal peptide (VIP) for the action of nitric oxide (NO) as a nonadrenergic noncholinergic inhibitory mediator was investigated regarding effects on migrating myoelectric complex (MMC) in rat. Animals were supplied with implanted bipolar electrodes at 5, 15 and 25 cm distal to pylorus for electromyography of small intestine. First, basal recordings with saline were followed by intravenous infusions of glyceryl trinitrate or VIP at different infusion rates to achieve dose-response relationships. Second, effects of different doses of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NNA) were studied. Third, the action of L-NNA (1 mg kg-1) on the effect of VIP (500 pmol kg-1 min-1), and of the VIP receptor antagonist (4-Cl-D-Phe6, Leu17), VIP (45 nmol 20 min-1), on the action of glyceryl trinitrate (44 nmol kg-1 min-1) was investigated. Glyceryl trinitrate prolonged the MMC cycle length from 16.3 +/- 1.3 to 44.9 +/- 8.0 min (P < 0.001), while VIP completely disrupted the MMC for the whole infusion period (P < 0.05). Higher doses of either compound induced quiescence. L-NNA shortened MMC cycle length from 14.7 +/- 1.2 to 8.6 +/- 1.4 min (P < 0.05), increased its propagation velocity from 2.0 +/- 0.4 to 18.3 +/- 8.4 cm min-1 (P < 0.01) and increased calculated length from 6.3 +/- 1.0 to 55.4 +/- 18.4 cm (P < 0.01). Pretreatment with (4-Cl-D-Phe6, Leu17) VIP blocked the inhibitory action of glyceryl trinitrate and preserved MMC pattern (P < 0.05). In contrast, L-NNA had no effect on the inhibition of MMC caused by VIP. Our results indicate that inhibition of MMC is related to production of NO, which may mediate its actions through VIP.

Nitric oxide modulates cholinergic neurotransmission in cat duodenum

1. Longitudinal muscle strips isolated from cat proximal duodenum were characterized by spontaneous phasic contractions. 2. Electrical field stimulation (EFS) (0.5 ms, 1-20 Hz, supramaximal voltage intensity for 40 sec) produced frequency-dependent contractions, and maximal amplitude was achieved at 10 Hz. The EFS-induced contractions were abolished either by atropine (10(-6) M) or by tetrodotoxin (3 x 10(-7) M). 3. The nitric oxide (NO) synthase blocker N infinity-nitro-L-arginine (L-NNA, 10(-4) M) or the inhibitor of the soluble guanylyl cyclase methylene blue (MB, 3 x 10(-5) M) increased the amplitude of the electrically evoked contractions. 4. L-Arginine (10(-3) M) or sodium nitroprusside (SNP, 10(-4) M) significantly decreased the amplitude of the EFS-induced, L-NNA- or MB-potentiated contractions as the effect of SNP was much more pronounced. 5. Neither L-NNA nor MB affected the contraction evoked by exogenous acetylcholine. 6. The L-NNA or MB-induced interruption of the L-arginine-NO pathway potentiated the electrically evoked cholinergic contractions, suggesting the inhibitory role of NO in the cholinergic neurotransmission realized probably at the pre-synaptic level in cat duodenum.

Functional role and histological demonstration of nitric-oxide-mediated inhibitory nerves in dog sphincter of Oddi

Nitric oxide (NO) plays an important physiological role in regulating gastrointestinal motility. Involvement of endogenous NO was evaluated in the response to non-adrenergic, non-cholinergic (NANC) nerve stimulation of the dog sphincter muscle of Oddi. Transmural electrical stimulation (TES), nicotine (10(-5) M) and K+ (10 mM) produced only a relaxation in the sphincter muscle strips contracted with substance P, which was not potentiated by atropine. The TES-induced relaxation was abolished by tetrodotoxin (3 x 10(-7) M) and oxyhaemoglobin (1.6 x 10(-5) M), but not affected by atropine (10(-7) M), propranolol (10(-7) M), phentolamine (10(-7) M), indomethacin (10(-6) M), cholecystokinin (CCK, 10(-8) M) and vasoactive intestinal polypeptide (VIP, 10(-8) M). The relaxation was also abolished by treatment with NG-nitro-L-arginine (L-NA, 10(-5) M), an NO synthase inhibitor. Nicotine produced a transient relaxation, which was abolished by tetrodotoxin, hexamethonium (10(-5) M) and L-NA, but not affected by atropine and NG-nitro-D-arginine (D-NA, 10(-5) M). The addition of K+ elicited a transient relaxation, which was abolished by tetrodotoxin and L-NA. The inhibitory effects of L-NA were antagonized by L-arginine (10(-3) M). The presence of neurons containing nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase was histochemically demonstrated in the sphincter of Oddi. These findings may indicate that TES, nicotine and K+ liberate NO from NANC inhibitory nerve which is involved in the relaxation of the dog sphincter of Oddi. The muscular tone does not seem to be regulated by cholinergic nerves under the experimental conditions used.

Intralipid-induced gastric relaxation is mediated via NO

In vitro, nitric oxide (NO) has been shown to be the neurotransmitter responsible for gastric relaxation. In vivo gastric relaxations can be controlled via reflex pathways originating in the duodenum. The aim of this study was to determine whether NO was involved in gastric relaxation in vivo in conscious dogs induced by intraduodenal administration of intralipid. Gastric tone was monitored with a flaccid bag introduced into the stomach via a gastric cannula and connected to a barostat. Intralipid administration into the duodenum caused a gastric relaxation (420 +/- 11 ml, n = 6) sensitive to inhibition by nitro-L-arginine (L-NNA) (5 mg kg-1 i.v.). This inhibitory effect of L-NNA was reversed by L-arginine (100 mg kg-1 i.v.).

IN CONCLUSION

intraduodenal administration of intralipid induces a gastric relaxation via a NO-dependent mechanism.

Nitric oxide in the peripheral nervous system

Nitric oxide (NO) is a neurotransmitter and neuromodulator in the central nervous system, but this small labile substance also seems to serve as a peripheral neurotransmitter. Abundant evidence is now available that NO, synthesized from L-arginine by NO synthase (NOS), is a nonadrenergic noncholinergic relaxant transmitter of gastrointestinal smooth muscle. Electrically induced nonadrenergic noncholinergic relaxations are antagonized by NOS inhibitors in vitro and in vivo. In a bioassay superfusion system, the release of a substance with the pharmacological characteristics of NO from a gastrointestinal smooth muscle preparation was detected; also, indirect measurements (e.g. of the NO metabolite nitrite or of the co-product of its synthesis L-citrulline) suggest NO release. Immunohistochemistry with antibodies raised against the neuronal NOS showed immunoreactivity in cell bodies of neurones in the myenteric plexus and in nerve fibres in the muscular layer. These data suggest that nerve endings, innervating smooth muscle, are able to release NO that will penetrate the cells to induce relaxation (i.e. nitrergic neurotransmission). It is unlikely that NO as such is stored and it is generally accepted that it is synthesized on demand when the nerve endings are excited, although the possibility of the release of a NO-containing molecule protecting it from degradation in the junction has been proposed. Other sources than neurones (interstitial cells, smooth muscle cells) for the NO involved in nonadrenergic noncholinergic inhibitory transmission have also been proposed. Using NADPH diaphorase as a marker for neuronal NOS, deficiency of the nitrergic innervation has been shown in isolated tissue from patients with infantile hypertrophic pyloric stenosis, achalasia and Hirschsprung's disease, suggesting that a lack of NO release might be involved in these disorders. Evidence in favour of nitrergic neurotransmission to smooth muscle has also been obtained in the respiratory and lower urinary tract, the corpora cavernosa and some blood vessels.

Nitric oxide formation is involved in vagal inhibition of the stomach of the trout (Salmo gairdneri)

Stimulation of the vagus nerves to isolated stomach preparations from trout (Salmo gairdneri) caused both excitation and inhibition of smooth muscle activity. Excitatory responses were partly reduced by atropine, suggesting that cholinergic neurons are involved. The atropine-resistant excitation could not readily be ascribed to a 'rebound' from preceding inhibition, to the production of prostaglandins, or to the activation of either adrenergic or capsaicin-sensitive fibres. Inhibitory responses were reduced by the nicotinic antagonist d-tubocurarine and more profoundly reduced by an inhibitor of nitric oxide synthase, NG-nitro-L-arginine. The latter effect was reversed by excess L-arginine. The nitric oxide donors sodium nitroprusside and nitroglycerine caused inhibition of the muscle. It is concluded that the vagal inhibitory postganglionic neurons are nitergic in this tissue.

The role of the L-arginine-nitric oxide pathway for peristalsis in the opossum oesophageal body

BACKGROUND

The aim of the study was to determine the effect of NG-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide (NO) synthesis, on primary peristalsis in the oesophageal body.

METHODS

Peristalsis was induced by pharyngeal stroking in 14 lightly anaesthetized opossums. Oesophageal pressures were monitored with a four-channel, perfused catheter assembly and registered with external transducers 1, 4, 7, and 10 cm proximal to the oesophagogastric junction. Propagation time was the time taken for a contraction to travel between two recording sites and was determined in the proximal, middle, and distal parts of the oesophagus (propagation time between 10 and 7 cm, 7 and 4 cm, and 4 and 1 cm recording sites, respectively).

RESULTS

L-NNA (10(-7)-10(-5) mol/kg) dose-dependently reduced propagation time of the contraction in the distal oesophagus from 1.13 +/- 0.24 sec to 0.27 +/- 0.19 sec, whereas propagation in the proximal and middle parts of the oesophagus was unaffected. NG-nitro-D-arginine (D-NNA; 10(-5) mol/kg) had no influence on propagation time. In animals treated with L-NNA (10(-5) mol/kg) atropine (50 micrograms/kg) had no influence on propagation time in any part of the oesophagus. L-Arginine (10(-4) mol/kg) had no influence on the propagation time in animals treated with L-NNA (10(-5) mol/kg) and atropine (50 micrograms/kg). Neither D-NNA (10(-5) mol/kg) nor L-NNA (10(-7)-10(-5) mol/kg) influenced the amplitude of the contractions at any of the recording sites. In animals given L-NNA (10(-5) mol/kg) atropine (50 micrograms/kg) reduced the amplitude of the contraction significantly only at the distal recording site (1-cm recording site) from 62.0 +/- 4.9 mmHg to 34.5 +/- 5.3 mmHg. L-Arginine (10(-4) mol/kg) had no effect on the amplitude of contractions.

CONCLUSION

The L-arginine-NO pathway plays a role in the control of primary peristalsic contractions of the oesophagus.

Participation of nitric oxide in the nicotine-induced relaxation of the cat lower esophageal sphincter

The participation of nitric oxide in the relaxation of the cat lower esophageal sphincter muscle strip in response to electrical field stimulation or administration of nicotine was studied. The nicotine-induced relaxation was mediated via a neuronal pathway, since it was inhibited by administration of hexamethonium or tetrodotoxin. Inhibition of nitric oxide biosynthesis by N-nitro-L-arginine decreased the relaxation induced by nicotine (50 microM) or field stimulation. With the maximal concentration of N-nitro-L-arginine (1 mM) electrical field stimulation-induced relaxation was abolished, while nicotine-induced relaxation decreased by 70%. L-Arginine (1 mM) partly restored this relaxation. Desensitization of P2x receptors by alpha, beta methylene-adenosine 5-triphosphate (alpha, beta-m-ATP) did not change the relaxation induced by either electrical field stimulation or administration of nicotine. It is therefore suggested that the field stimulation-induced relaxation is mediated by the release of nitric oxide, but in the nicotine-produced relaxation is only partly due to nitric oxide, other factor(s) might be also be involved.

Nitric oxide and gastric relaxation

Pentagastrin enhanced the volume increase caused by isobaric gastric distension in conscious dogs. This effect could be abolished by inhibitors of acid secretion and mimicked by histamine. The increased compliance after pentagastrin was not affected by L-nitroarginine (L-NNA), a blocker of nitric oxide (NO) synthase. L-NNA itself reduced the volume increases caused by isobaric gastric distension. Intralipid administration into the duodenum led to a gastric relaxation sensitive to inhibition by L-NNA. The inhibitory effect of L-NNA was partially reversed by L-arginine. Pentagastrin induces a gastric relaxation via a mechanism that involves gastric secretion but not nitric oxide, whereas intraduodenal intralipid induces a gastric relaxation via a NO-dependent mechanism.

Role of nitric oxide in mediating non-adrenergic non-cholinergic relaxation of the cat ileocecal sphincter

The participation of nitric oxide (NO) in field stimulation- or nicotine-evoked non-adrenergic non-cholinergic (NANC) relaxation of cat ileocecal sphincter was studied in vitro. During a 30 microM noradrenaline-induced contraction, both the application of electrical field stimulation (2-20 Hz, 0.2 ms, supramaximal current intensity, 10 s duration) and (-)-nicotine (10-500 microM) produced a tetrodotoxin-sensitive relaxation. The maximal relaxation was observed at 10 Hz or 100 microM (-)-nicotine. In 12 out of 19 strips the pretreatment with N omega-nitro-L-arginine (100 microM) decreased the amplitude of the field stimulation-evoked relaxation, while in the remaining strips the relaxation was transformed into a contraction. By increasing the concentration of N omega-nitro-L-arginine up to 1 mM all strips responded to field stimulation with a frequency-dependent tetrodotoxin-resistant contraction. N omega-Nitro-L-arginine (100 microM) completely inhibited the nicotine-induced relaxation. L-Arginine (1 mM) restored the amplitude of both field stimulation- and nicotine-evoked relaxations. These data indicate that NO appears to be involved in both field stimulation- and nicotine-evoked NANC relaxations. Evidence has been obtained for the existence of tetrodotoxin-resistant NANC contraction in cat ileocecal sphincter.

Contribution of ATP and nitric oxide to NANC inhibitory transmission in rat pyloric sphincter

1. Changes in isometric tension were recorded from circular muscle strips of rat pyloric sphincter in vitro, in response to electrical field stimulation and exogenously applied muscle relaxants. 2. Concentration-response relationships were studied for relaxation to exogenously applied adenosine 5'-triphosphate (ATP) and two analogues, 2-methylthioATP (2-MeSATP) and alpha,beta-methylene ATP (alpha,beta-MeATP). These drugs evoked concentration-dependent relaxation of rat pyloric sphincter with an order of potency 2-MeSATP > ATP >> alpha,beta-MeATP, indicating the presence of P2y-purinoceptors. The IC50 value of each nucleotide was: 2-MeSATP, 5.0 x 10(-8); ATP, 7.9 x 10(-6) M; alpha,beta-MeATP showed only slight activity at a concentration of 0.1 mM. 3. Frequency-response relationships for relaxations evoked by electrical field stimulation (EFS) were studied in the absence and presence of 10 microM NG-nitro-L-arginine methyl ester (L-NAME, an inhibitor of nitric oxide (NO) synthesis) and 20 microM reactive blue 2 (a P2y-purinoceptor antagonist). It was found that these substances significantly reduced the relaxant response of rat pyloric sphincter to EFS by 40% and 50% respectively. In the presence of both L-NAME and reactive blue 2 the responses were reduced by 75%. 4. Concentration-response relationships were studied for ATP and 2-MeSATP in the presence of L-NAME. It was found that L-NAME did not significantly inhibit the relaxant responses to these drugs. 5. Concentration-response relationships for ATP and noradrenaline were studied in the presence of reactive blue 2 (20 microM); the P2y-antagonist significantly inhibited the relaxant response to ATP, but not that to noradrenaline. 6. The distribution of nitric oxide synthase in rat pyloric sphincter was investigated immunohistochemically,with immunoreactive nerve fibres found throughout the circular muscle layer and myenteric plexus of the sphincter.7. While abundant vasoactive intestinal polypeptide (VIP)-containing nerve fibres were demonstrated immunohistochemically in the pyloric sphincter, relaxations to VIP (1 nM-0.3 micro M) were not observed in this preparation.8. It is concluded that ATP, acting through P2y-purinoceptors, and NO contribute to NANC inhibitory neurotransmission in rat pyloric sphincter. NO appeared to contribute to the later component of NANCrelaxation. The action of ATP was not mediated by NO, and VIP did not contribute to the NANCinhibitory responses in this preparation.

Cholecystokinin and nitric oxide in transient lower esophageal sphincter relaxation to gastric distention in dogs

BACKGROUND/AIMS

Transient lower esophageal sphincter relaxations have been found to be involved in gastroesophageal reflux. The purpose of this study was to determine whether cholecystokinin (CCK) and nitric oxide are involved in the occurrence of these relaxations.

METHODS

Pharyngeal, esophageal, lower esophageal sphincter, and gastric pressures were monitored in five dogs through a cervical esophagostomy. Gastric distentions with air, at a constant pressure of 1.56 kPa, were performed for 30-minute sessions using a barostat.

RESULTS

During gastric distention at 1.56 kPa, transient relaxations occurred at a mean rate of 7.2 +/- 0.6 every 30 minutes. CCK-8 infused intravenously (0.1-1 microgram.kg-1.h-1) dose dependently increased the occurrence of relaxations while it was reduced by the CCK-A receptor antagonist devazepide but not the CCK-B antagonist L365260, both administered intravenously in a dose range of 0.1-100 micrograms/kg. The two antagonists administered intracerebroventricularly (1 microgram/kg) did not modify the occurrence of relaxations. Both devazepide and L365260 (10 micrograms/kg) reduced the CCK-induced relaxations, but devazepide was more potent. The nitric oxide synthase inhibitor NG-nitro-L-arginine-methyl ester (20 mg/kg) reduced the number of relaxations during gastric distention in the presence or absence of CCK infusion. This effect was reversed by L-arginine but not D-arginine (200 mg/kg).

CONCLUSIONS

CCK is involved in the occurrence of transient lower esophageal sphincter relaxations through peripheral CCK-A receptors and an L-arginine nitric oxide pathway.

Transmitter mechanisms in vagal afferent-induced reduction of lower oesophageal sphincter (LOS) pressure in the rat

The extrinsic neural pathways and transmitter mechanisms involved in neural influences controlling lower oesophageal sphincter (LOS) pressure have been evaluated in three groups of experiments in urethane anaesthetized rats. A miniature perfused sleeve/sidehole catheter measured gastric, LOS and oesophageal pressures. Group 1: Vago-vagal and vago-spinal reflex pathways were activated simultaneously via the central nervous system by stimulation of the central cut end of the left vagus. This caused a prolonged drop in LOS pressure with a rapid onset and a slow return to baseline. Subsequent right (bilateral) vagotomy in these animals increased basal LOSP (P < 0.001). Central vagal stimulation-induced reduction of LOSP was not significantly changed in amplitude but was shorter in duration (P < 0.01) than before bilateral vagotomy. IV administration of the 5-HT3 receptor antagonist granisetron (50 micrograms/kg), after bilateral vagotomy had no effect on the response to central vagal stimulation. The nitric oxide (NO) synthase inhibitor L-nitroarginine methyl ester (L-NAME) (100 mg/kg) reduced the depth of relaxation (P < 0.01) and temporarily increased basal LOSP. Propranolol (1.5 mg/kg, i.v.) subsequently increased basal LOSP (P < 0.01), but had no further effect on the vagal stimulation-induced reduction in LOSP. Alpha adrenergic blockade with phentolamine (1 mg/kg, i.v.) decreased basal LOSP (P < 0.01), and nearly abolished the response to vagal stimulation (P < 0.01). Group 2: Both alpha 1- and alpha 2-adrenoceptors were shown to be involved by the combined use of the more selective antagonists yohimbine (1 mg/kg, i.v.) and prazosin (200 micrograms/kg) in place of phentolamine. Group 3: To observe neurotransmitter mechanisms in the vago-vagal pathway, central left vagal stimulation was performed after left vagotomy, and subsequently after blockade of sympathetic motor pathways with guanethidine (5 mg/kg), leaving intact efferent pathways in the right vagus. Guanethidine increased basal LOSP (P < 0.01), and reduced the duration of vagal-induced LOS relaxation (P < 0.05). Depth of relaxation was unchanged. Subsequently, granisetron and L-NAME had no significant effects. Finally, additional right vagotomy abolished the remaining response. Our data indicate the existence of vago-spinal and vago-vagal inhibitory reflex pathways to the rat LOS. The inhibitory vago-spinal pathway is mainly alpha-adrenergic, and has a minor NO-mediated component, but no 5-HT3 receptor-mediated mechanism. In the vago-vagal pathway, no significant involvement of NO-mediated or 5-HT3 receptor-mediated effects was observed. Other non-adrenergic inhibitory mechanisms were, however, apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

Some characteristics of the muscularis mucosae of the cat lower esophageal sphincter

1. The contractile activity of muscularis mucosae strips isolated from cat lower esophageal sphincter (LES) was studied. 2. LES muscularis mucosae strips were characterized by spontaneous phasic contractions. 3. Acetylcholine (ACh) at a threshold concentration of 10(-8) M dose-dependently increased the basal tone and decreased the amplitude of the phasic contractions. Noradrenaline (NA) also increased the basal tone but at a higher threshold concentration (10(-6) M). 4. Nicotine (N) at concentrations of 5 x 10(-5)-10(-4) M induced a relaxation of the LES muscularis mucosae. The N-induced relaxation was tetrodotoxin (TTX) (10(-6) M) sensitive and was insignificantly reduced after guanethidine (5 x 10(-6) M) plus scopolamine (5 x 10(-6) M) or propranolol (10(-6) M). The N-induced relaxation was strongly decreased by the blocker of nitric oxide (NO) synthesis N omega Nitro-L-Arginine (L-NNA) (10(-4) M). The relaxation was restored after addition of L-arginine (10(-3) M). 5. These results suggest the involvement of NO in the N-induced relaxation of the muscularis mucosae.

Nitric oxide mediates inhibitory nerve effects in human esophagus and lower esophageal sphincter

The effect of inhibition of nitric oxide synthase on nonadrenergic, noncholinergic nerve-mediated responses in circular smooth muscle of the human esophageal body and lower esophageal sphincter (LES) was examined in vitro. Tissues were obtained from 10 patients (eight esophageal resection for cancer, two transplant donors). Muscle strips from the LES developed significant spontaneous tension (11.6 +/- 2.1 mN/mm2, N = 6) and relaxed in response to electrical stimulation. The nitric oxide synthase inhibitor, N omega-nitro-L-arginine (NNA), at 10(-5) M, inhibited the relaxation, but had no significant effect on the spontaneous tension (13.0 +/- 2.6 mN/mm2, P = 0.07). Esophageal body strips developed little spontaneous tension, demonstrated an "off" contraction following the cessation of the electrical stimulus, and when contracted with 10(-5) M carbachol, relaxed during electrical stimulation. NNA (10(-5) M) inhibited the off contraction and the relaxation seen after carbachol and unmasked a prominent intrastimulus contraction. This intrastimulus contraction was enhanced by eserine and inhibited by atropine and tetrodotoxin. NNA showed similar potency in the esophageal body and LES and its effects were reversed by L-arginine, but not D-arginine. The results indicate that nitric oxide is an important mediator for nonadrenergic, noncholinergic nerve effects in the human esophagus and lower esophageal sphincter.

Ileal distention relaxes the canine colon: a model of megacolon?

BACKGROUND/AIMS

Reflex relaxation is a mechanism whereby the colon can show short-term dilatation in the absence of mechanical obstruction. This study investigated the tonic response of the canine colon to ileal distention and its pharmacological control.

METHODS

In four dogs, the tone of the proximal colon was recorded by a barostat during distention of the terminal ileum.

RESULTS

Ileal distention inhibited ileal motility and relaxed the colon. Adrenergic blockade by propranolol plus phentolamine, nicotinic blockade by hexamethonium, and the nitric oxide synthase inhibitor N omega-nitro-L-arginine methylester significantly increased resting tone of the colon but did not inhibit relaxation induced by ileal distention. Muscarinic blockade by atropine completely relaxed the colon, and no further decrease in tone was observed after ileal distention. The neurokinin 2 antagonist SR48968 did not alter colonic tone.

CONCLUSIONS

The barostat was able to monitor resting tone of the canine colon, which was shown to be under inhibitory control by adrenergic, cholinergic-nicotinic, and nitric oxide-like transmitters. Inhibition of colonic tone by ileal distention was not mediated solely by adrenergic, cholinergic-nicotinic, or nitric oxide mechanisms. Reflex relaxation, possibly predisposing to acute colonic dilatation, may be activated by multiple mechanisms that may differ from those controlling resting tone.

The role of the L-arginine/nitric oxide pathway for relaxation of the human lower oesophageal sphincter

Smooth muscle specimens were taken from the oesophagogastric junction (OGJ) in patients operated on for gastrointestinal malignancies not involving the OGJ. The smooth muscle bundles of the inner, circular layer of the OGJ were richly innervated by fine nerve fibres staining positively for NADPH diaphorase. The outer longitudinal layer had a markedly lower number of NADPH-diaphorase positive nerve fibres. When the preparations were suspended in organ baths for recording of isometric tension, they developed active tension. Transmural field stimulation (TMS) induced frequency-dependent relaxations, which were abolished by NG-nitro-L-arginine (L-NNA; 10(-4) M), and were often converted to atropine-sensitive contractions. The effect of L-NNA was concentration-dependent, and the concentration-response curve for L-NNA was shifted to the right by L-arginine pre-incubation. The enantiomer NG-nitro-D-arginine (10(-4) M) also showed inhibitory actions on the responses to TMS, but significantly less than L-NNA. Relaxant responses to vasoactive intestinal polypeptide (VIP), forskolin, and sodium nitroprusside were unaffected by L-NNA pre-incubation. Exposure to a 124 mM K+ solution resulted in a biphasic relaxation of the preparations. This relaxation was not seen in preparations treated with scorpion venom (20 micrograms ml-1) or L-NNA (10(-4) M). Instead, a contractile response to 124 mM K+ solution was found. The results suggest that NANC responses to electrical stimulation of nerves in the human OGJ are mediated by a product generated from L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Esophageal physiology and pathophysiology

This article presents the normal physiology of esophageal peristalsis. It discusses current approaches to the diagnosis and treatment of primary disorders of the esophagus, including achalasia, nutcracker esophagus, diffuse esophageal spasm, as well as the secondary disorder, scleroderma.

Patients with achalasia lack nitric oxide synthase in the gastro-oesophageal junction

The abnormal function of the lower oesophageal sphincter in achalasia is likely to be due to impaired nonadrenergic, noncholinergic (NANC) inhibitory input. Since recent studies in animals suggest that nitric oxide (NO) is implicated physiologically in the inhibitory responses of the lower oesophageal sphincter, we have investigated whether the synthesis of NO is altered in the gastro-oesophageal junction of patients with achalasia. NO synthase activity was investigated in samples of tissue from the gastro-oesophageal junction obtained during surgery in eight patients with typical achalasia and six non-achalasic controls who underwent oesophagectomy for reasons other than sphincter dysfunction. The NO synthase activity was determined by the transformation of 14C-L-arginine into 14C-L-citrulline in tissue homogenates. In addition, immunohistochemical staining of the tissues was performed using a polyclonal antibody raised against a peptide sequence of rat brain NO synthase. Furthermore, the relaxant response to an exogenous NO donor (sodium nitroprusside, SNP) was measured in vitro in muscle strips obtained from two patients with achalasia and in two non-achalasic controls. NO synthase activity was detected in each of the samples obtained from six control patients (0.59 +/- 0.21 pmol mg-1 min-1; mean +/- SE). By contrast, none of the samples obtained from the eight patients with achalasia had any detectable NO synthase activity. Immunohistochemical studies confirmed the presence of NO synthase in the myenteric plexus of the gastro-oesophageal junction of control patients and its absence in achalasia. SNP relaxed muscle strips precontracted with bethanechol in both control samples and those from patients with achalasia.(ABSTRACT TRUNCATED AT 250 WORDS)