Role of nitric oxide- and vasoactive intestinal polypeptide-containing neurones in human gastric fundus strip relaxations

The Possible Involvement of Glucagon-like Peptide-2 in the Regulation of Food Intake through the Gut-Brain Axis

Food intake regulation is a complex mechanism involving the interaction between central and peripheral structures. Among the latter, the gastrointestinal tract represents one of the main sources of both nervous and hormonal signals, which reach the central nervous system that integrates them and sends the resulting information downstream to effector organs involved in energy homeostasis. Gut hormones released by nutrient-sensing enteroendocrine cells can send signals to central structures involved in the regulation of food intake through more than one mechanism. One of these is through the modulation of gastric motor phenomena known to be a source of peripheral satiety signals. In the present review, our attention will be focused on the ability of the glucagon-like peptide 2 (GLP-2) hormone to modulate gastrointestinal motor activity and discuss how its effects could be related to peripheral satiety signals generated in the stomach and involved in the regulation of food intake through the gut-brain axis. A better understanding of the possible role of GLP-2 in regulating food intake through the gut-brain axis could represent a starting point for the development of new strategies to treat some pathological conditions, such as obesity.

Accelerated Electron Ionization-Induced Changes in the Myenteric Plexus of the Rat Stomach

The influence of accelerated electrons on neuronal structures is scarcely explored compared to gamma and X-rays. This study aims to investigate the effects of accelerated electron radiation on some pivotal neurotransmitter circuits (cholinergic and serotonergic) of rats' myenteric plexus. Male Wistar rats were irradiated with an electron beam (9 MeV, 5 Gy) generated by a multimodality linear accelerator. The contractile activity of isolated smooth muscle samples from the gastric corpus was measured. Furthermore, an electrical stimulation (200 μs, 20 Hz, 50 s, 60 V) was performed on the samples and an assessment of the cholinergic and serotonergic circuits was made. Five days after irradiation, the recorded mechanical responses were biphasic-contraction/relaxation in controls and contraction/contraction in irradiated samples. The nature of the contractile phase of control samples was cholinergic with serotonin involvement. The relaxation phase involved ACh-induced nitric oxide release from gastric neurons. There was a significant increase in serotonergic involvement during the first and second contractile phases of the irradiated samples, along with a diminished role of acetylcholine in the first phase. This study demonstrates an increased involvement of serotonergic neurotransmitter circuits in the gastric myenteric plexus caused by radiation with accelerated electrons.

Effects of hydrogen sulfide on relaxation responses in the lower esophageal sphincter in rabbits: the potential role of potassium channels

Hydrogen sulfide (H2S) is a significant physiologic inhibitory neurotransmitter. The main goal of this research was to examine the contribution of diverse potassium (K+) channels and nitric oxide (NO) in mediating the H2S effect on electrical field stimulation (EFS)-induced neurogenic contractile responses in the lower esophageal sphincter (LES). EFS-induced contractile responses of rabbit isolated LES strips were recorded using force transducers in organ baths that contain Krebs-Henseleit solutions (20 ml). Cumulative doses of NaHS, L-cysteine, PAG, and AOAA were evaluated in NO-dependent and NO-independent groups. The experiments were conducted again in the presence of K+ channel blockers. In both NO-dependent and NO-independent groups, NaHS, L-cysteine, PAG, and AOAA significantly reduced EFS-induced contractile responses. In the NO-dependent group, the effect of NaHS and L-cysteine decreased in the presence of 4-AP, and also the effect of NaHS decreased in the NO-dependent and independent group in the presence of TEA. In the NO-independent group, K+ channel blockers didn't change L-cysteine-induced relaxations. K+ channel blockers had no impact on the effects of PAG and AOAA. In addition, NaHS significantly relaxed 80-mM KCl-induced contractions, whereas L-cysteine, PAG, and AOAA did not. In the present study, H2S decreased the amplitudes of EFS-induced contraction responses. These results suggest that Kv channels and NO significantly contribute to exogenous H2S and endogenous H2S precursor L-cysteine inhibitory effect on lower esophageal sphincter smooth muscle.

From the organ bath to the whole person: a review of human colonic motility

Motor function of the colon is essential for health. Our current understanding of the mechanisms that underlie colonic motility are based upon a range of experimental techniques, including molecular biology, single cell studies, recordings from muscle strips, analysis of part or whole organ ex vivo through to in vivo human recordings. For the surgeon involved in the clinical management of colonic conditions this amounts to a formidable volume of material. Here, we synthesize the key findings from these various experimental approaches so that surgeons can be better armed to deal with the complexities of the colon.

Influence and Implications of the Molecular Paradigm of Nitric Oxide Underlying Inflammatory Reactions of the Gastrointestinal Tract of Dog: A Major Hallmark of Inflammatory Bowel Disease

Nitric oxide (NO), a pleiotropic free radical messenger molecule, is responsible for the various cellular function of the gastrointestinal mucosa. It plays a major role in the maintenance of perfusion, regulation of microvascular, epithelial permeability, and immune functions. Nitric oxide exerts its beneficial effect on the initiation and maintenance of inflammation in human inflammatory bowel disease (IBD). But the accelerated production of NO triggers activation of the inducible form of the NO synthase enzyme (iNOS) that leads to damages of the intestinal membrane. Nitric oxide synthase enzyme is responsible for the higher production of NO from l-arginine and causes an inflammatory condition in the intestinal epithelium. Nitric oxide induces nitrative DNA damage and oxidative DNA damage in the cellular system. Accelerated production of NO enhances iNOS activity that is associated with cytotoxicity and apoptosis of gastrointestinal epithelial cells in the dog. Chronic inflammation leads to angiogenesis that is modulated by the immune system in IBD. Chronic inflammation is a major risk factor for the development of gastrointestinal malignancies. Nitric oxide participates in mucosal inflammation in the intestine through invigoration of NO synthase enzyme. The intrinsic complex mechanism is correlated with the inflammation in the gastrointestinal tract and is also correlated with the expression of iNOS, enzymatic activity and NO production. Nitric oxide employs a significant role in modulating epithelial permeability with accelerated immune response in acute colitis. But the enormous generation of NO causes adverse effects on the mucosal cell during the inflammatory process in IBD. In this review, a complex episode of NO generation with altered biochemical pathways was assessed for the regulation of mucosal inflammation in inflammatory bowel disease of dogs. This review is a unique compilation of the role of NO in the pathogenesis of inflammatory bowel disease of dogs. Nitric oxide plays a key role in modulating cancer in the gastrointestinal tract. This review seeks to explore the characteristics of NO as a major hallmark of canine inflammatory bowel diseases.

Nitric Oxide: From Gastric Motility to Gastric Dysmotility

It is known that nitric oxide (NO) plays a key physiological role in the control of gastrointestinal (GI) motor phenomena. In this respect, NO is considered as the main non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter responsible for smooth muscle relaxation. Moreover, many substances (including hormones) have been reported to modulate NO production leading to changes in motor responses, further underlying the importance of this molecule in the control of GI motility. An impaired NO production/release has indeed been reported to be implicated in some GI dysmotility. In this article we wanted to focus on the influence of NO on gastric motility by summarizing knowledge regarding its role in both physiological and pathological conditions. The main role of NO on regulating gastric smooth muscle motor responses, with particular reference to NO synthases expression and signaling pathways, is discussed. A deeper knowledge of nitrergic mechanisms is important for a better understanding of their involvement in gastric pathophysiological conditions of hypo- or hyper-motility states and for future therapeutic approaches. A possible role of substances which, by interfering with NO production, could prove useful in managing such motor disorders has been advanced.

Effect of Evodiamine on Rat Colonic Hypermotility Induced by Water Avoidance Stress and the Underlying Mechanism

Background and Aim

EVO is a natural alkaloid that reportedly has potential value in regulating gastrointestinal motility, but this conclusion remains controversial, and the molecular mechanism is unclear. In this study, we aimed to explore the effect of short-chain fatty acids on rat colonic hypermotility induced by water avoidance stress and the underlying mechanism.

Methods

We constructed a hypermotile rat model by chronic water avoidance stress, and Western blot was used to detect the protein level of nNOS in colon tissue. The organ bath and multichannel physiological signal acquisition systems were used to examine the spontaneous contractions of smooth muscle strips. The whole-cell patch-clamp technique was used to investigate L-type voltage-dependent calcium and BK_Ca channel currents in colonic smooth muscle cells.

Results

EVO inhibited the spontaneous contractions of colonic smooth muscle strips in a dose-dependent manner. Moreover, EVO decreased the fecal output induced by chronic water avoidance stress. TTX did not block the inhibitory effect of EVO on spontaneous colon contractions, while L-NNA, a selective nNOS synthase inhibitor, did partially abolish this inhibitory effect. The protein expression of nNOS in the colon tissues of rats administered EVO was significantly increased compared to that in control rats. EVO reversibly inhibited the L-type calcium channel current without changing the steady-state activation or inactivation in colonic smooth muscle cells. EVO significantly inhibited the BK_Ca current but did not change the shape of the I-V curves.

Conclusion

EVO inhibits gastrointestinal motility by inhibiting L-type calcium and BK_Ca channels in colonic smooth muscle cells and indirectly interacting with nNOS.

The identification of neuronal control pathways supplying effector tissues in the stomach

The stomach acts as a buffer between the ingestion of food and its processing in the small intestine. It signals to the brain to modulate food intake and it in turn regulates the passage of a nutrient-rich fluid, containing partly digested food, into the duodenum. These processes need to be finely controlled, for example to restrict reflux into the esophagus and to transfer digesta to the duodenum at an appropriate rate. Thus, the efferent pathways that control gastric volume, gastric peristalsis and digestive juice production are critically important. We review these pathways with an emphasis on the identities of the final motor neurons and comparisons between species. The major types of motor neurons arising from gastric enteric ganglia are as follows: immunohistochemically distinguishable excitatory and inhibitory muscle motor neurons; four neuron types innervating mucosal effectors (parietal cells, chief cells, gastrin cells and somatostatin cells); and vasodilator neurons. Sympathetic efferent neurons innervate intramural arteries, myenteric ganglia and gastric muscle. Vagal efferent neurons with cell bodies in the brain stem do not directly innervate gastric effector tissues; they are pre-enteric neurons that innervate each type of gastric enteric motor neuron. The principal transmitters and co-transmitters of gastric motor neurons, as well as key immunohistochemical markers, are the same in rat, pig, human and other species.

Sacral nerve stimulation increases gastric accommodation in rats: a spinal afferent and vagal efferent pathway

Impaired gastric accommodation (GA) has been frequently reported in various gastrointestinal diseases. No standard treatment strategy is available for treating impaired GA. We explored the possible effect of sacral nerve stimulation (SNS) on GA and discovered a spinal afferent and vagal efferent mechanism in rats. Sprague-Dawley rats (450-500 g) with a chronically implanted gastric cannula and ECG electrodes were studied in a series of sessions to study: 1) the effects of SNS with different parameters on gastric tone, compliance, and accommodation using a barostat device; two sets of parameters were tested as follows: parameter 1) 5 Hz, 500 µs, 10 s on 90 s off; 90% motor threshold and parameter 2) same as parameter 1 but 25 Hz; 2) the involvement of spinal afferent pathway via detecting c-fos immunoreactive (IR) cells in the nucleus of the solitary tract (NTS) of the brain; 3) the involvement of vagal efferent activity via the spectral analysis of heart rate variability derived from the ECG; and 4) the nitrergic mechanism, N^ω-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase (NOS) inhibitor, was given before SNS at 5 Hz. Compared with sham-SNS: 1) SNS at 5 Hz inhibited gastric tone and increased gastric compliance and GA. No difference was noted between the stimulation frequencies of 5 and 25 Hz. 2) SNS increased the expression of c-fos in the NTS. 3) SNS increased cardiac vagal efferent activity and decreased the sympathovagal ratio. 4) l-NAME blocked the relaxation effect of SNS. In conclusion, SNS with certain parameters relaxes gastric fundus and improves gastric accommodation mediated via a spinal afferent and vagal efferent pathway.NEW & NOTEWORTHY Currently, there is no adequate medical therapy for impaired gastric accommodation, since medications that relax the fundus often impair antral peristalsis and thus further delay gastric emptying that is commonly seen in patients with functional dyspepsia or gastroparesis. The advantage of the potential sacral nerve stimulation therapy is that it improves gastric accommodation by enhancing vagal activity, and the enhanced vagal activity would lead to enhanced antral peristalsis rather than inhibiting it.

Morphological and Immunohistochemical Characterization of Human Intrinsic Gastric Neurons

Our knowledge about human gastric enteric neuron types is even more limited than that of human intestinal types. Here, we immunohistochemically stained wholemounts and sections of gastric specimens obtained from 18 tumor-resected patients. Myenteric wholemounts were labeled for choline acetyl transferase (ChAT), neuronal nitric oxide synthase (NOS), and the human neuronal protein HuC/D (as pan-neuronal marker for quantitative analysis) or alternatively for neurofilament (for morphological evaluation). ChAT-positive neurons outnumbered NOS-positive neurons (56 vs. 27%), and neurons negative for both markers accounted for 17%. Two larger groups of neurons (each between 12 and 14%) costained for ChAT and vasoactive intestinal peptide (VIP) or for NOS and VIP, respectively. Clear morphochemical correlation was found for uniaxonal stubby type I neurons (ChAT+; putative excitatory inter- or motor neurons), for uniaxonal spiny type I neurons (NOS+/VIP+; putative inhibitory motor or interneurons), and for multiaxonal type II neurons (ChAT+; putative afferent neurons; immunostaining of additional wholemounts revealed their coreactivity for somatostatin). Whereas these latter neuron types were already known from the human intestine, the morphology of gastric myenteric neurons coreactive for ChAT and VIP was newly described: they had numerous short, extremely thin dendrites and resembled, together with their cell bodies, a "hairy" head. In our sections, nerve fibers coreactive for ChAT and VIP were commonly found only in the mucosa. We suggest these myenteric ChAT+/VIP+/hairy neurons to be mucosal effector neurons. In contrast to myenteric neurons, the much less common submucosal neurons were not embedded in a continuous plexus and did not display any clear morphochemical phenotypes.

Impaired neural pathway in gastric muscles of patients with diabetes

To explore the pathogenic mechanism of diabetic gastropathy, we investigated differences in response to electrical field stimulation (EFS) of gastric muscles from diabetic and non-diabetic (control) patients. Gastric specimens were obtained from 34 patients and 45 controls who underwent gastrectomy for early gastric cancer. Using organ bath techniques, we examined peak and nadir values of contraction under EFS. To examine responses to purinergic and nitrergic inhibition without cholinergic innervation, atropine, MRS2500, and N-nitro-L-arginine (L-NNA) were added sequentially to the organ bath. Tetrodotoxin (TTX) was used to confirm that the responses to EFS were mediated via neural stimulation. In the absence of pharmacological agents, peak contraction amplitude was greater in non-diabetic controls compared to diabetics only in the distal longitudinal gastric muscles. However, the nadir was greater in controls than in patients in both proximal and distal gastric circular muscles. Addition of MRS2500 could not decrease the nadir in both controls and patients, both in the proximal and distal stomach. However, L-NNA completely reversed the relaxation. TTX had no further effect on nadir. In conclusion, impaired inhibitory nitrergic neural pathway in both proximal and distal stomach and impaired excitatory cholinergic neural pathway in the distal stomach may contribute to the pathogenic mechanism underlying diabetic gastropathy.

Autoimmune comorbidity in achalasia patients

BACKGROUND AND AIM

Idiopathic achalasia is a rare esophageal motor disorder. The disease state manifests local and systemic inflammation, and it appears that an autoimmune component and specific autoantibodies participate in the pathogenesis. The study aims to determine the prevalence of autoimmune and chronic inflammatory diseases in patients with achalasia and compare the results with those from patients with gastroesophageal reflux disease (GERD).

METHODS

It was a cross-sectional and included 114 patients with idiopathic achalasia and 114 age-matched and sex-matched control patients with GERD. Data on the presence of autoimmune and inflammatory diseases, the time of presentation, and any family history of autoimmune disease were obtained from the hospital's medical records.

RESULTS

Seventy three (64%) were female patients (mean age: 42.3 ± 15.5; median disease duration: 12 months). We identified the presence of autoimmune disease in 19 patients with achalasia (16.7%), hypothyroidism was the main diagnosis, and it was present in 52.6% of patients compared with 4.2% in controls. Thirteen of the 19 achalasia patients (68.4%) with autoimmune disease had history of familial autoimmunity. We identified 11 achalasia (9.6%) and 5 GERD patients (4.16%) with an inflammatory condition. Compared with the GERD, the achalasia group was 3.8 times more likely to have an autoimmune disease (95% CI: 1.47-9.83), 3.0 times more likely to have thyroidopathies (95% CI: 1.00-9.03), and 3.02 times more likely to suffer from any chronic inflammatory disease (95% CI: 1.65-6.20).

CONCLUSIONS

The non-negligible number of patients with autoimmune diseases identified among the patients with idiopathic achalasia supports the hypothesis that achalasia has an autoimmune component.

Influence of amino acids on gastric adaptive relaxation (accommodation) in rats as evaluated with a barostat

Aim: The present study aimed to evaluate the effects of selected straight alkyl chain, hydroxylated chain and branched chain amino acids on gastric adaptive relaxation, as these have previously been shown to have differing effects on gastric emptying. Materials and Methods: Gastric adaptive relaxation was evaluated using a barostat in rats under urethane anesthesia. The pressure within the balloon, introduced from the mouth to the stomach, was changed stepwise from 1 to 8 mmHg. The increased volume just after the increase of balloon pressure was defined as distension-induced gastric adaptive relaxation (accommodation). Amino acids were administered orally or intravenously. Results: As compared with control rats administered with distilled water, those rats that were orally administered amino acids having straight alkyl chain and extra hydroxylated alkyl chain, such as glycine and l-serine, had significantly enhanced gastric adaptive relaxation, but administration of l-alanine and l-threonine did not. Branched chain amino acids, such as l-isoleucine, l-leucine and l-valine, also did not significantly influence gastric adaptive relaxation. Glycine and l-serine showed the same efficacy when administered intravenously. Conclusion: Among the amino acids evaluated in the present study, glycine and l-serine significantly enhanced gastric adaptive relaxation, suggesting that short alkyl chain amino acids may enhance gastric adaptive relaxation as compared with the other amino acids. These findings may suggest that glycine and l-serine would be useful in the therapy of functional dyspepsia, especially for early satiety, because the dysfunction of adaptive relaxation is one of the causes of early satiety.

Upper GI Disorders: Pathophysiology and Current Therapeutic Approaches

Symptoms referable to the upper digestive tract are associated with abnormalities of upper gastric neuromuscular function including abnormalities of motility, sensation, and absorption. Of the upper digestive tract, the stomach is of particular importance in its role in symptom generation and is highlighted in this chapter. Gastric symptoms can be associated with alterations in the rates of gastric emptying, impaired accommodation, heightened gastric sensation, or alterations in gastric myoelectrical activity and contractility. Treatment of gastric neuromuscular disorders requires an understanding of pathophysiology of the disorders, the appropriate use and interpretation of diagnostic tests, and the knowledge of effective treatment options. This chapter covers the pathophysiology and current treatment approaches to disorders of the upper gastrointestinal tract, focusing on classic disorders of the stomach, particularly gastroparesis and functional dyspepsia.

Nitrergic Pathway Is the Main Contributing Mechanism in the Human Gastric Fundus Relaxation: An In Vitro Study

Background

Human gastric fundus relaxation is mediated by intrinsic inhibitory pathway. We investigated the roles of nitrergic and purinergic pathways, two known inhibitory factors in gastric motility, on spontaneous and nerve-evoked contractions in human gastric fundus muscles.

Methods

Gastric fundus muscle strips (12 circular and 13 longitudinal) were obtained from patients without previous gastrointestinal motility disorder who underwent gastrectomy for stomach cancer. Using these specimens, we examined basal tone, peak, amplitude, and frequency of spontaneous contractions, and peak and nadir values under electrical field stimulation (EFS, 150 V, 0.3 ms, 10 Hz, 20 s). To examine responses to purinergic and nitrergic inhibition without cholinergic innervation, atropine (muscarinic antagonist, 1 μM), MRS2500 (a purinergic P2Y1 receptor antagonist, 1 μM), and N-nitro-L-arginine (L-NNA, a nitric oxide synthase inhibitor, 100 μM) were added sequentially for spontaneous and electrically-stimulated contractions. Tetrodotoxin was used to confirm any neuronal involvement.

Results

In spontaneous contraction, L-NNA increased basal tone and peak in both muscle layers, while amplitude and frequency were unaffected. EFS (up to 10 Hz) uniformly induced initial contraction and subsequent relaxation in a frequency-dependent manner. Atropine abolished initial on-contraction and induced only relaxation during EFS. While MRS2500 showed no additional influence, L-NNA reversed relaxation (p = 0.012 in circular muscle, and p = 0.006 in longitudinal muscle). Tetrodotoxin abolished any EFS-induced motor response.

Conclusions

The relaxation of human gastric fundus muscle is reduced by nitrergic inhibition. Hence, nitrergic pathway appears to be the main mechanism for the human gastric fundus relaxation.

The effect of levosulpiride on in vitro motor patterns in the human gastric fundus, antrum, and jejunum

BACKGROUND

Levosulpiride is a 5HT4 agonist/D2 antagonist prokinetic agent used to improve gastric emptying in patients with functional dyspepsia or gastroparesis. The aim of this study was to characterize its effect on the main in vitro motility patterns in the human fundus, antrum, and jejunum.

METHODS

Circular muscle strips from human stomach (antrum and fundus) and jejunum, obtained from 46 patients undergoing bariatric surgery, were studied using organ baths. Enteric motor neurons (EMNs) were stimulated by electrical field stimulation (EFS).

KEY RESULTS

Levosulpiride, caused an increase in the EFS-induced cholinergic contractions in the gastric antrum (+37 ± 15.18% at 100 μM, pEC50 = 4.46 ± 0.14; p < 0.05, n = 8) and jejunum (+45.4 ± 22.03% at 100 μM, pEC50 = 3.78 ± 6.81; p < 0.05, n = 5), but not in the gastric fundus. It also caused a slight decrease in tone and frequency of spontaneous contractions in the jejunum, but did not have any major effect on tone or spontaneous contractions in the stomach. It did not have any effect on EFS-induced relaxations mediated by nitric oxide (NO) in the stomach (antrum and fundus) and by NO and ATP in the jejunum.

CONCLUSIONS & INFERENCES

Our results suggest that the prokinetic effects of levosulpiride in humans are mainly due to the facilitation of the release of acetylcholine by enteric motor neurons in the gastric antrum and the jejunum.

Abnormal Barrier Function in Gastrointestinal Disorders

There is increasing concern in identifying the mechanisms underlying the intimate control of the intestinal barrier, as deregulation of its function is strongly associated with digestive (organic and functional) and a number of non-digestive (schizophrenia, diabetes, sepsis, among others) disorders. The intestinal barrier is a complex and effective defensive functional system that operates to limit luminal antigen access to the internal milieu while maintaining nutrient and electrolyte absorption. Intestinal permeability to substances is mainly determined by the physicochemical properties of the barrier, with the epithelium, mucosal immunity, and neural activity playing a major role. In functional gastrointestinal disorders (FGIDs), the absence of structural or biochemical abnormalities that explain chronic symptoms is probably close to its end, as recent research is providing evidence of structural gut alterations, at least in certain subsets, mainly in functional dyspepsia (FD) and irritable bowel syndrome (IBS). These alterations are associated with increased permeability, which seems to reflect mucosal inflammation and neural activation. The participation of each anatomical and functional component of barrier function in homeostasis and intestinal dysfunction is described, with a special focus on FGIDs.

[Paradoxical sphincters in the abdomen]

Nitric oxide molecules serve as neurotransmitters to relax smooth muscle tension in many parts of the body. In humans and other mammals they play an important role for correct smooth muscle function in unusual locations. We previously described this mechanism (Stelzner, Chirurg. doi:10.1007/s00104-014-2777-z, 2014) using the occlusive mechanism of the upper and lower esophageal sphincters as an example. Cells producing nitric oxide can be found in the gastric fundus, the anorectal continence organ, vesicourethraltract and also in the uterine cervix in the final trimester of pregnancy. In all these locations they serve as elements of anatomical sphincter structures that have a paradoxical function. These observations confirm the points made in the introduction of this article on the stretch sphincter mechanism of the lower esophageal sphincter and the treatment of gastroesophageal reflux disease by retensioning of the esophagus in the diaphragmatic hiatus. In particular, high-resolution esophageal manometry of the lower esophageal sphincter can easily detect every functional disturbance caused by gastric plication and such changes were to be expected based on what we described in articles I and II.

H2 Receptor-Mediated Relaxation of Circular Smooth Muscle in Human Gastric Corpus: the Role of Nitric Oxide (NO)

This study was designed to examine the effects of histamine on gastric motility and its specific receptor in the circular smooth muscle of the human gastric corpus. Histamine mainly produced tonic relaxation in a concentration-dependent and reversible manner, although histamine enhanced contractility in a minor portion of tissues tested. Histamine-induced tonic relaxation was nerve-insensitive because pretreatment with nerve blockers cocktail (NBC) did not inhibit relaxation. Additionally, K⁺ channel blockers, such as tetraethylammonium (TEA), apamin (APA), and glibenclamide (Glib), had no effect. However, N^G-nitro-L-arginine methyl ester (L-NAME) and 1H-(1,2,4)oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC), did inhibit histamine-induced tonic relaxation. In particular, histamine-induced tonic relaxation was converted to tonic contraction by pretreatment with L-NAME. Ranitidine, the H₂ receptor blocker, inhibited histamine-induced tonic relaxation. These findings suggest that histamine produced relaxation in circular smooth muscle of human gastric smooth muscle through H₂ receptor and NO/sGC pathways.

Gastroduodenal mechanisms underlying functional gastric disorders

Functional dyspepsia (FD), a disorder thought to originate from the gastroduodenum, is one of the most prevalent functional gastrointestinal disorders. In this review, we focused on gastroduodenal mechanisms involved in the pathophysiology of FD. The roles of impaired gastric accommodation, delayed gastric emptying, hypersensitivity to gastric distention and to luminal agents, altered mucosal integrity, low-grade inflammation and psychological stress are reviewed. The underlying pathophysiology in FD is probably multifactorial, involving a combination of several of these factors, ultimately leading to symptom pattern and severity.

Translational neuropharmacology: the use of human isolated gastrointestinal tissues

Translational sciences increasingly emphasize the measurement of functions in native human tissues. However, such studies must confront variations in patient age, gender, genetic background and disease. Here, these are discussed with reference to neuromuscular and neurosecretory functions of the human gastrointestinal (GI) tract. Tissues are obtained after informed consent, in collaboration with surgeons (surgical techniques help minimize variables) and pathologists. Given the difficulties of directly recording from human myenteric neurones (embedded between muscle layers), enteric motor nerve functions are studied by measuring muscle contractions/relaxations evoked by electrical stimulation of intrinsic nerves; responses are regionally dependent, often involving cholinergic and nitrergic phenotypes. Enteric sensory functions can be studied by evoking the peristaltic reflex, involving enteric sensory and motor nerves, but this has rarely been achieved. As submucosal neurones are more accessible (after removing the mucosa), direct neuronal recordings are possible. Neurosecretory functions are studied by measuring changes in short-circuit current across the mucosa. For all experiments, basic questions must be addressed. Because tissues are from patients, what are the controls and the influence of disease? How long does it take before function fully recovers? What is the impact of age- and gender-related differences? What is the optimal sample size? Addressing these and other questions minimizes variability and raises the scientific credibility of human tissue research. Such studies also reduce animal use. Further, the many differences between animal and human GI functions also means that human tissue research must question the ethical validity of using strains of animals with unproved translational significance.

Gastric sensitivity and reflexes: basic mechanisms underlying clinical problems

Both reflex and sensory mechanisms control the function of the stomach, and disturbances in these mechanisms may explain the pathophysiology of disorders of gastric function. The objective of this report is to perform a literature-based critical analysis of new, relevant or conflicting information on gastric sensitivity and reflexes, with particular emphasis on the comprehensive integration of basic and clinical research data. The stomach exerts both phasic and tonic muscular (contractile and relaxatory) activity. Gastric tone determines the capacity of the stomach and mediates both gastric accommodation to a meal as well as gastric emptying, by partial relaxation or progressive recontraction, respectively. Perception and reflex afferent pathways from the stomach are activated independently by specific stimuli, suggesting that the terminal nerve endings operate as specialized receptors. Particularly, perception appears to be related to stimulation of tension receptors, while the existence of volume receptors in the stomach is uncertain. Reliable techniques have been developed to measure gastric perception and reflexes both in experimental and clinical conditions, and have facilitated the identification of abnormal responses in patients with gastric disorders. Gastroparesis is characterised by impaired gastric tone and contractility, whereas patients with functional dyspepsia have impaired accommodation, associated with antral distention and increased gastric sensitivity. An integrated view of fragmented knowledge allows the design of pathophysiological models in an attempt to explain disorders of gastric function, and may facilitate the development of mechanistically orientated treatments.

Nitric oxide synthase gene polymorphisms in functional dyspepsia

OBJECTIVE

Nitrinergic control is important in meal-induced satiety. The aim of this study was to assess functional polymorphisms in nitric oxide synthase (NOS) genes in the susceptibility to functional dyspepsia (FD).

METHODS

Genomic DNA from 89 patients with FD and 180 healthy subjects matched for age and gender were typed for the gene of neuronal NOS (nNOS, rs2682826), inducible NOS (iNOS, rs2297518) and a variable number tandem repeat in intron 4 of endothelial NOS (eNOS). Patients ingested 500 mL of Ensure(®) during a 20 min period and dyspeptic symptoms were scored.

RESULTS

Genotype frequencies of eNOS and iNOS were not significantly different between FD patients and controls. The frequency of the T allele in nNOS was significantly higher in FD patients compared to the controls (49 vs. 16 %; odds ratio 5.01; 95 % confidence interval 2.83-9.01; p < 0.05). Patients with the T allele in the nNOS polymorphism reported a higher satiation score than those with the CC genotype during the nutrition drink test (median 179 vs. 117; p < 0.05).

CONCLUSION

The nNOS gene polymorphism is associated with susceptibility to FD and influences satiation in FD patients. Our data support the importance of NOS gene polymorphisms in the pathogenesis of FD.

Tetrahydrobiopterin deficiency induces gastroparesis in newborn mice

Pyloric stenosis, the most common infant gastrointestinal disease, has no known etiology and clinically presents as abnormal gastric emptying with evidence of pyloric muscle hypertrophy. Whether abnormalities in gastric muscle contraction and/or relaxation have a role in this condition is poorly known, but gastroparesis is commonly observed in association with delayed gastric emptying in adults. Therefore, we evaluated the tetrahydrobiopterin (BH4)-deficient newborn mouse model of this disease (hph-1) and hypothesized that their gastric muscle properties are impaired, when compared with wild-type control animals. In vitro studies evaluating the age-dependent gastric fundus muscle contraction and relaxation potential were conducted. Compared with wild-type mice, the hph-1 stomach content/body weight ratio was significantly increased in newborn but not juvenile or adult animals, confirming abnormal gastric emptying. Gastric tissue neuronal nitric oxide synthase (nNOS) protein expression was upregulated in both newborn and adult hph-1 mice, but in the former there was evidence of enzyme uncoupling and higher tissue superoxide generation when compared with same age-matched animals. As opposed to the lack of strain differences in the U46619-induced force, the newborn hph-1 gastric muscle carbachol-induced contraction and nNOS-dependent relaxation were significantly reduced (P < 0.01). These group differences were not present in juvenile or adult mice. Preincubation with BH4 significantly enhanced the newborn hph-1, but not wild-type, gastric muscle contraction. In conclusion, changes compatible with gastroparesis are present in the newborn mouse model of pyloric stenosis. The role of BH4 deficiency and possibly associated gastroparesis in the pathogenesis of infantile pyloric stenosis warrants further investigation.

Heme deficiency of soluble guanylate cyclase induces gastroparesis

BACKGROUND

Soluble guanylate cyclase (sGC) is the principal target of nitric oxide (NO) to control gastrointestinal motility. The consequence on nitrergic signaling and gut motility of inducing a heme-free status of sGC, as induced by oxidative stress, was investigated.

METHODS

sGCβ1 (H105F) knock-in (apo-sGC) mice, which express heme-free sGC that has basal activity, but cannot be stimulated by NO, were generated.

KEY RESULTS

Diethylenetriamine NONOate did not increase sGC activity in gastrointestinal tissue of apo-sGC mice. Exogenous NO did not induce relaxation in fundic, jejunal and colonic strips, and pyloric rings of apo-sGC mice. The stomach was enlarged in apo-sGC mice with hypertrophy of the muscularis externa of the fundus and pylorus. In addition, gastric emptying and intestinal transit were delayed and whole-gut transit time was increased in the apo-sGC mice, while distal colonic transit time was maintained. The nitrergic relaxant responses to electrical field stimulation at 1-4 Hz were abolished in fundic and jejunal strips from apo-sGC mice, but in pyloric rings and colonic strips, only the response at 1 Hz was abolished, indicating the contribution of other transmitters than NO.

CONCLUSIONS & INFERENCES

The results indicate that the gastrointestinal consequences of switching from a native sGC to a heme-free sGC, which cannot be stimulated by NO, are most pronounced at the level of the stomach establishing a pivotal role of the activation of sGC by NO in normal gastric functioning. In addition, delayed intestinal transit was observed, indicating that nitrergic activation of sGC also plays a role in the lower gastrointestinal tract.

Evaluation of adaptive relaxation of the rat stomach using an orally inserted balloon instead of surgical intervention by demonstrating the effects of capsaicin and Nω-nitro-L-arginine methylester

Gastric functions such as adaptive relaxation have usually been monitored in rats using a surgically inserted barostat's balloon. However, surgery causes physiological damage to the rat stomach. This study is an investigation of adaptive relaxation of the rat stomach using a slightly modified balloon, which is introduced into the stomach through the mouth of anesthetized rats without the need for balloon surgery, attached to a brostat. In this case, the balloon was placed between the fore-stomach and the fundus, but towards the fore-stomach. The balloon volume increased gradually just after an increment in the balloon pressure, and reached a plateau within 1 min. This increased volume just after the increment of the balloon pressure was defined as adaptive relaxation. Adaptive relaxation increased with pressure increases in a pressure dependent manner. Pre-treatment with Nω-nitro-L-arginine methylester (30 mg/kg, i.v.) caused this adaptive relaxation to be significantly inhibited as compared with the control. On the contrary, adaptive relaxation was significantly enhanced by pre-treatment with capsaicin (0.5 mg/kg, p.o.). These findings show that this method is both useful for investigating the physiology of adaptive relaxation of the stomach without surgery and to show that nitric oxide plays an important role in the adaptive relaxation of the stomach as reported previously.

Regional- and agonist-dependent facilitation of human neurogastrointestinal functions by motilin receptor agonists

BACKGROUND AND PURPOSE

Delayed gastric emptying is poorly managed. Motilin agonists are potential treatments but inadequate understanding into how enteric nerve functions are stimulated compromises drug/dose selection. Resolution is hampered by extreme species dependency so methods were developed to study human gastrointestinal neuromuscular activities and the neurobiology of motilin.

EXPERIMENTAL APPROACH

Protocols to study neuromuscular activities were developed for different regions of human stomach and intestine (71 patients) using circular muscle preparations and electrical field stimulation (EFS) of intrinsic nerves. Other tissues were fixed for immunohistochemistry.

KEY RESULTS

EFS evoked contractions and/or relaxations via cholinergic and nitrergic neurons, with additional tachykinergic activity in colon; these were consistent after 154 min (longer if stored overnight). Motilin 1-300 nM and the selective motilin agonist GSK962040 0.1-30 µM acted pre-junctionally to strongly facilitate cholinergic contractions of the antrum (E(max) ≈ 1000% for motilin), with smaller increases in fundus, duodenum and ileum; high concentrations increased baseline muscle tension in fundus and small intestine. There were minimal effects in the colon. In the antrum, cholinergic facilitation by motilin faded irregularly, even with peptidase inhibitors, whereas facilitation by GSK962040 was long lasting. Motilin receptor immunoreactivity was identified in muscle and myenteric plexus predominantly in the upper gut, co-expressed with choline acetyltransferase in neurons.

CONCLUSIONS AND IMPLICATIONS

Motilin and GSK962040 strongly facilitated cholinergic activity in the antrum, with lower activity in fundus and small intestine only. Facilitation by motilin was short lived, consistent with participation in migrating motor complexes. Long-lasting facilitation by GSK962040 suggests different receptor interactions and potential for clinical evaluation.

Functional role of vasoactive intestinal polypeptide in inhibitory motor innervation in the mouse internal anal sphincter

There is evidence that vasoactive intestinal polypeptide (VIP) participates in inhibitory neuromuscular transmission (NMT) in the internal anal sphincter (IAS). However, specific details concerning VIP-ergic NMT are limited, largely because of difficulties in selectively blocking other inhibitory neural pathways. The present study used the selective P2Y1 receptor antagonist MRS2500 (1 μm) and the nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA; 100 μm) to block purinergic and nitrergic NMT to characterize non-purinergic, non-nitrergic (NNNP) inhibitory NMT and the role of VIP in this response. Nerves were stimulated with electrical field stimulation (0.1-20 Hz, 4-60 s) and the associated changes in contractile and electrical activity measured in non-adrenergic, non-cholinergic conditions in the IAS of wild-type and VIP(-/-) mice. Electrical field stimulation gave rise to frequency-dependent relaxation and hyperpolarization that was blocked by tetrodotoxin. Responses during brief trains of stimuli (4 s) were mediated by purinergic and nitrergic NMT. During longer stimulus trains, an NNNP relaxation and hyperpolarization developed slowly and persisted for several minutes beyond the end of the stimulus train. The NNNP NMT was abolished by VIP6-28 (30 μm), absent in the VIP(-/-) mouse and mimicked by exogenous VIP (1-100 nm). Immunoreactivity for VIP was co-localized with neuronal nitric oxide synthase in varicose intramuscular fibres but was not detected in the VIP(-/-) mouse IAS. In conclusion, this study identified an ultraslow component of inhibitory NMT in the IAS mediated by VIP. In vivo, this pathway may be activated with larger rectal distensions, leading to a more prolonged period of anal relaxation.

High k(+)-induced relaxation by nitric oxide in human gastric fundus

This study was designed to elucidate high K(+)-induced relaxation in the human gastric fundus. Circular smooth muscle from the human gastric fundus greater curvature showed stretch-dependent high K(+) (50 mM)-induced contractions. However, longitudinal smooth muscle produced stretch-dependent high K(+)-induced relaxation. We investigated several relaxation mechanisms to understand the reason for the discrepancy. Protein kinase inhibitors such as KT 5823 (1 µM) and KT 5720 (1 µM) which block protein kinases (PKG and PKA) had no effect on high K(+)-induced relaxation. K(+) channel blockers except 4-aminopyridine (4-AP), a voltage-dependent K(+) channel (K(V)) blocker, did not affect high K(+)-induced relaxation. However, N(G)-nitro-L-arginine and 1H-(1,2,4)oxadiazolo (4,3-A)quinoxalin-1-one, an inhibitors of soluble guanylate cyclase (sGC) and 4-AP inhibited relaxation and reversed relaxation to contraction. High K(+)-induced relaxation of the human gastric fundus was observed only in the longitudinal muscles from the greater curvature. These data suggest that the longitudinal muscle of the human gastric fundus greater curvature produced high K(+)-induced relaxation that was activated by the nitric oxide/sGC pathway through a K(V) channel-dependent mechanism.

Myogenic regional responsiveness to cholinergic and vipergic stimulation in human colon

BACKGROUND

Differences in the actions of enteric neurotransmitters on colonic circular and longitudinal muscle layers have not been clearly determined, nor the possible existence of intrinsic myogenic phenotypes that might contribute to regional differences in human colon motor activity. The aim of this study was to analyze the direct pharmaco-mechanical coupling of carbachol (CCh) and vasoactive intestinal polypeptide (VIP) on human colonic smooth muscle strips and cells.

METHODS

Circular and longitudinal muscle strips and cells were obtained from 15 human specimens of ascending and sigmoid colon. Both isometric tension on muscle strips and contraction and relaxation on cells were measured in response to increasing CCh and VIP concentrations.

KEY RESULTS

Circular muscle strips of ascending colon were more sensitive to the effect of CCh than that of sigmoid colon, EC(50) values being, respectively, 4.15μmolL(-1) and 8.47μmolL(-1) (P<0.05), although there were no differences in maximal responses. No regional differences were observed in longitudinal muscle strips or in smooth muscle cells. Maximal responses to CCh were higher on circular than longitudinal muscle strips and cells throughout the colon. A greater sensitivity to VIP was observed in ascending colon compared with sigmoid colon, both in circular (EC(50:) 0.041 and 0.15μmolL(-1) , respectively, P<0.01) and longitudinal (EC(50:) 0.043 and 0.09μmolL(-1) , respectively, P<0.05) strips, and similar differences were observed in longitudinal smooth muscle cells (EC(50:) 44.85 and 75.24nmolL(-1) , respectively, P<0.05).

CONCLUSIONS & INFERENCES

Regional myogenic differences in pharmaco-mechanical coupling between the enteric neurotransmitters and smooth muscle contribute to the complex regional motor patterns of human colon.

Nitric Oxide-mediated Relaxation by High K in Human Gastric Longitudinal Smooth Muscle

This study was designed to elucidate high-K(+)induced response of circular and longitudinal smooth muscle from human gastric corpus using isometric contraction. Contraction from circular and longitudinal muscle stripes of gastric corpus greater curvature and lesser curvature were compared. Circular smooth muscle from corpus greater curvature showed high K(+) (50 mM)-induced tonic contraction. On the contrary, however, longitudinal smooth muscle strips showed high K(+) (50 mM)-induced sustained relaxation. To find out the reason for the discrepancy we tested several relaxation mechanisms. Protein kinase blockers like KT5720, PKA inhibitor, and KT5823, PKG inhibitor, did not affect high K(+)-induced relaxation. K(+) channel blockers like tetraethylammonium (TEA), apamin (APA), glibenclamide (Glib) and barium (Ba(2+)) also had no effect. However, N(G)-nitro-L-arginine (L-NNA) and 1H-(1,2,4) oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC) and 4-AP (4-aminopyridine), voltage-dependent K(+) channel (K(V)) blocker, inhibited high K(+)-induced relaxation, hence reversing to tonic contraction. High K(+)-induced relaxation was observed in gastric corpus of human stomach, but only in the longitudinal muscles from greater curvature not lesser curvature. L-NNA, ODQ and K(V) channel blocker sensitive high K(+)-induced relaxation in longitudinal muscle of higher portion of corpus was also observed. These results suggest that longitudinal smooth muscle from greater curvature of gastric corpus produced high K(+)-induced relaxation which was activated by NO/sGC pathway and by K(V) channel dependent mechanism.

Effects of smoking cessation on gastric emptying in smokers

BACKGROUND

Smoking cessation can lead to changes in appetite and weight gain in some patients; thus, smoking cessation may alter gastrointestinal motility. Effects of smoking cessation on gastric emptying in smokers have not been established.

AIM

This study sought to determine how smoking cessation affects gastric emptying in smokers.

METHODS

Participant group comprised 53 habitual smokers and 12 healthy nonsmokers. Habitual smokers were treated for 2 months with transdermal nicotine patches. Gastric emptying was studied using C acetate breath tests at the beginning of the study, and at 1 week and 9 weeks after cessation of patch use. Maximal CO2 excretion time (Tmax), CO2 excretion half-life (T1/2), and parameters beta and kappa, representing initial and subsequent gastric-emptying phases, respectively, were determined using conventional formulae.

RESULTS

Before smoking cessation, Tmax was reached significantly later in smokers (0.94+/-0.3 h, P=0.014) than in controls (0.89+/-0.1 h). At 1 week after the end of treatment, Tmax was significantly decreased (from 1.05+/-0.32 h to 0.72+/-0.64 h, P=0.003). T1/2 also tended to decrease, but not significantly. Although beta was decreased significantly (from 2.46+/-0.40 to 2.17+/-0.58, P=0.022), kappa was unchanged. However, by 9 weeks after the end of treatment, Tmax (1.28+/-0.69 h) had increased to levels seen before treatment.

CONCLUSIONS

Smoking cessation temporarily accelerates gastric emptying, and decreases in beta suggest that initial-phase gastric emptying accelerates after smoking cessation. The temporary acceleration of gastric emptying after smoking cessation may be involved in the temporary increase in appetite and weight gain seen after smoking cessation.

Relaxation patterns of human gastric corporal smooth muscle by cyclic nucleotides producing agents

To elucidate the mechanism of cyclic nucleotides, such as adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5' -cyclic monophosphate (cGMP), in the regulation of human gastric motility, we examined the effects of forskolin (FSK), isoproterenol (ISO) and sodium nitroprusside (SNP) on the spontaneous, high K(+) and acetylcholine (ACh)-induced contractions of corporal circular smooth muscle in human stomach. Gastric circular smooth muscle showed regular spontaneous contraction, and FSK, ISO and SNP inhibited its phasic contraction and basal tone in a concentration-dependent manner. High K(+) (50 mM) produced sustained tonic contraction, and ACh (10 microM) produced initial transient contraction followed by later sustained tonic contraction with superimposed phasic contractions. FSK, ISO and SNP inhibited high K(+)-induced tonic contraction and also ACh-induced phasic and tonic contraction in a reversible manner. Nifedipine (1 microM), inhibitor of voltage-dependent L-type calcium current (VDCC(L)), almost abolished ACh-induced phasic contractions. These findings suggest that FSK, ISO and SNP, which are known cyclic nucleotide stimulators, inhibit smooth muscle contraction in human stomach partly via inhibition of VDCC(L).

Exogenous nitrergic pathway involved in the regulation of gastric myoelectrical activity in dogs

OBJECTIVE

Although the effect of nitric oxide (NO) on gastric motility has been investigated in numerous studies, its effects on gastric slow waves and spike activity which regulate gastric motility remained largely unknown. The aim of this study was to test the hypothesis that NO would impair gastric slow waves by reducing their regularity and amplitude as well as contraction-related spike activity.

MATERIAL AND METHODS

The study required four sessions in 8 dogs, 2 weeks after the implantation of four pairs of electrodes along the greater curvature of the stomach. In each session, saline, L-arginine (L-Arg) (75 mg/kg), NG-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg) or L-Arg + L-NAME was given intravenously (IV) after a 30-min baseline recording in the fasting state. A solid test meal (200 g) was ingested 30 min after the IV injection of one of the medications. Gastric myoelectrical activity was recorded for 30 min at baseline, 30 min after the IV injection and 60 min after the meal.

RESULTS

The frequency, amplitude and rhythmicity of gastric slow waves were not affected by NO. L-NAME significantly increased spike activity in the fasting state but not in the fed state. L-Arg did not reduce the number of spike bursts per minute (NSPM) in the fed state. Postprandially, there was a significant decrease in slow wave frequency but a substantial increase in the strength and frequency of spike activity.

CONCLUSIONS

Exogenous NO has no effect on the frequency, amplitude or regularity of gastric slow waves; inhibition of NO increases spike activity in the fasting state but not in the fed state.

Tests of gastric neuromuscular function

Tests of gastric neuromuscular function are used to evaluate patients with symptoms referable to the upper digestive tract. These symptoms can be associated with alterations in the rates of gastric emptying, impaired accommodation, heightened gastric sensation, or alterations in gastric myoelectrical function and contractility. Management of gastric neuromuscular disorders requires an understanding of pathophysiology and treatment options as well as the appropriate use and interpretation of diagnostic tests. These tests include measures of gastric emptying; contractility; electrical activity; regional gastric motility of the fundus, antrum, and pylorus; and tests of sensation and compliance. Tests are also being developed to improve our understanding of the afferent sensory pathways from the stomach to the central nervous system that mediate gastric sensation in health and gastric disorders. This article reviews tests of gastric function and provides a basic description of the tests, the methodologies behind them, descriptions of the physiology that they assess, and their clinical utility.

Role of nitric oxide produced by constitutive and inducible nitric oxide synthases in the mouse gastric fundus

In the present study, the role of nitric oxide (NO) produced by constitutive and inducible nitric oxide synthases (cNOS and iNOS, resepctively) on the contraction and relaxation of fundus in normal and lipopolysaccharide (LPS)-treated mice was examined. A whole fundic ring isolated from mice pretreated with reserpine was mounted in an organ bath containing Krebs' solution with 0.001 mmol/L atropine. Rings were contracted initially by 5-hydroxytryptamine (5-HT; 0.03 mmol/L) before relaxation was induced using ATP (0.03 mmol/L), ADP (0.03 mmol/L), pentoxifylline (0.002 mmol/L), electrical field stimulation (EFS; 50 V, 1 msec, 50 Hz, 3 min) and L-arginine (0.05 mmol/L). All drugs and EFS induced significant relaxation of isolated rings. The relaxations induced were significantly inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 1.0 mmol/L). However, the iNOS inhibitors L-N(6)-(1-iminoethyl) lysine hydrochloride (L-NIL; 1.0 mmol/L) and amino guanidine (AMG; 1.0 mmol/L) had no significant effect on tissue relaxation. Then, the relaxant effects of 0.03 mmol/L ATP were tested on precontracted isolated fundic rings taken from 10 mg/kg LPS-treated animals. The non-selective NOS inhibitor L-NAME (10 mg/kg), the iNOS inhibitors L-NIL (3 mg/kg) and AMG (20 mg/kg) and betamethasone (0.1 mg/kg) were used to examine the role of NO produced by iNOS in the relaxation responses. It was found that the level of contraction induced by 0.03 mmol/L 5-HT in rings isolated from LPS-treated animals was significantly (P < 0.5) less than that in rings from untreated mice. However, precontracted tissues from LPS-treated mice were significantly relaxed by ATP and the relaxation response to ATP was significantly inhibited by L-NIL, ANG and betamethasone, but not by L-NAME. We suggest that, in LPS-treated mice, the production of NO from iNOS produces a reduction in the contractile response, as well as a decrease in NO formation by cNOS, resulting in changes to smooth muscle cell function.

The use of gastric electrical signals for algorithm for automatic eating detection in dogs

Food ingestion increases fundic impedance (FI) and reduces antral slow wave rate (SWR). Our aim was to determine if such changes can be integrated into an algorithm for automatic eating detection (AED). When incorporated in implantable medical devices, AED can time treatment to food intake without need for patient input. Four dogs were implanted with fundic and antral electrodes, connected to an implantable recording device. Changes in FI and SWR induced by fixed meals of different weights were determined, and were used to build an AED algorithm. Its performance was then tested on the same animals given an ad libitum access to food. The effects of gastric balloon distension and nitroglycerin on SWR and FI were also tested. Fixed meals reduced SWR in a weight-dependent manner, R(2) = 0.936, P < 0.05 baseline compared to 50, 100, 200 and 400 g. Meals increased FI above baseline in a weight-dependent manner; R(2) = 0.994, P < 0.05 baseline compared to 200 and 400 g. During ad libitum intake, the AED algorithm detected 86% of all meals > or =15 g. Gastric distension reduced SWR and increased FI. Nitroglycerin reduced SWR. AED, using changes in FI and gastric SWR is feasible. Changes in FI and SWR are induced primarily by the presence of food in the stomach.

Roles of putative neurotransmitters in the regulation of gastric and intestinal slow waves in conscious dogs

BACKGROUND AND AIMS

Slow waves play an important role in controlling the frequency and propagation of gastrointestinal contractions. However, mechanisms involved in the modulation of slow wave activity in vivo are still unclear. In this study, the roles of different neurotransmitters in the regulation of gastrointestinal slow waves were investigated in conscious dogs.

METHODS

Female dogs implanted with electrodes in the stomach and the small bowel were used in a seven-session study. Gastrointestinal myoelectrical activity was recorded at baseline and after i.v. saline, atropine, atropine methyl nitrate, guanethidine, Nomega-nitro-L-arginine (L-NNA), ondansetron or naloxone.

RESULTS

Both atropine and atropine methyl nitrate induced tachygastria, bradygastria and arrhythmia. No difference was noted in the effects between atropine and atropine methyl nitrate. L-NNA increased the dominant frequency of small-intestinal slow waves but had no effect on gastric slow waves. Guanethidine, ondansetron and naloxone did not affect the dominant frequency, power or percentage of normal gastrointestinal slow waves.

CONCLUSION

Acetylcholine acting at muscarinic receptors seems to play an important role in the regulation of gastric slow waves. Nitric oxide may play a role in modulating intestinal slow waves but not gastric slow waves. Sympathetic pathways, 5-HT(3) receptors and opioid receptors (especially micro-opioid receptors) do not play a role in the regulation of gastric or intestinal slow waves under normal physiological conditions.

Do gap junctions play a role in nerve transmissions as well as pacing in mouse intestine?

Varicosities of nitrergic and other nerves end on deep muscular plexus interstitial cells of Cajal or on CD34-positive, c-kit-negative fibroblast-like cells. Both cell types connect to outer circular muscle by gap junctions, which may transmit nerve messages to muscle. We tested the hypotheses that gap junctions transmit pacing messages from interstitial cells of Cajal of the myenteric plexus. Effects of inhibitors of gap junction conductance were studied on paced contractions and nerve transmissions in small segments of circular muscle of mouse intestine. Using electrical field stimulation parameters (50 V/cm, 5 pps, and 0.5 ms) which evoke near maximal responses to nitrergic, cholinergic, and apamin-sensitive nerve stimulation, we isolated inhibitory responses to nitrergic nerves, inhibitory responses to apamin-sensitive nerves and excitatory responses to cholinergic nerves. 18beta-Glycyrrhetinic acid (10, 30, and 100 microM), octanol (0.1, 0.3, and 1 mM) and gap peptides (300 microM of (40)Gap27, (43)Gap26, (37,43)Gap27) all failed to abolish neurotransmission. 18beta-Glycyrrhetinic acid inhibited frequencies of paced contractions, likely owing to inhibition of l-type Ca(2+) channels in smooth muscle, but octanol or gap peptides did not. 18beta-Glycyrrhetinic acid and octanol, but not gap peptides, reduced the amplitudes of spontaneous and nerve-induced contractions. These reductions paralleled reductions in contractions to exogenous carbachol. Additional experiments with gap peptides in both longitudinal and circular muscle segments after N(G)-nitro-l-arginine and TTX revealed no effects on pacing frequencies. We conclude that gap junction coupling may not be necessary for pacing or nerve transmission to the circular muscle of the mouse intestine.

Vasoactive intestinal peptide receptor subtypes and signalling pathways involved in relaxation of human stomach

Vasoactive intestinal peptide (VIP) relaxes smooth muscle by interacting with receptors coupled to cAMP- or cGMP-signalling pathways. Their relative contribution to human gastric relaxation is unknown. This study aimed at investigating, in terms of biological activity, receptor expression and related signalling pathways, the action of VIP separately on the human fundus and the antrum. VIP caused greater relaxation of smooth muscle cells (SMC) and strips of the antrum presenting on the former a higher efficacy and potency (ED(50): 0.53 +/- 0.17 nmol L(-1)) than on the fundus (ED(50): 3.4 +/- 1.4 nmol L(-1)). On both fundus and antrum strips, its effect was tetrodotoxin insentitive. Reverse transcriptase-polymerase chain reaction analysis showed the sole expression of VPAC2 and natriuretic peptide clearance receptors, with VPAC2 being more abundant in the antrum. Functional regional differences in receptor-related signalling pathways were found. Activation of the cAMP-pathway by forskolin or its inhibition by adenylate cyclase (2'5'-dideoxyadenosine) or kinase (Rp-cAMPs) inhibitors had more pronounced effects on antrum SMC. Activation of the cGMP-pathway by sodium nitroprusside or its inhibition by guanylate cyclase (LY83583) or kinase (KT5823) inhibitors had more effects on fundus SMC, on which a higher expression of endothelial nitric oxide synthase was found. In conclusion, regional differences in VIP action on human stomach are related to distinct myogenic properties of SMC of the antrum and the fundus.

Colonic electrical stimulation regulates colonic transit via the nitrergic pathway in rats

Gastrointestinal electrical stimulation has been proposed for the treatment of gastrointestinal motor disorders. However, little is known about potential roles of colonic electrical stimulation (CES). The aim of this study was to evaluate the effect and mechanism of CES on colonic transit in conscious rats. Male rats (N = 14) were equipped with a pair of colonic serosal electrodes for stimulation and a catheter in the colon. Colonic transit was assessed in four randomized sessions with or without CES and with or without nitric oxide synthesis blocker, L-NNA, by calculating the output of phenol red from the anus every 10 min for 90 min. Results were as follows. (1) CES with trains of short pulses significantly enhanced colonic transit. Colonic emptying was 57.3 +/- 6.1% in the control session and 81.9 +/- 4.6% with CES at 90 min, reflecting a 43% increase. (2) L-NNA delayed colonic transit compared with saline and prevented the accelerative effect of CES on colonic transit. We conclude that CES has an excitatory effect on colonic transit and this excitatory effect may be mediated via the nitrergic pathway.

Serum from achalasia patients alters neurochemical coding in the myenteric plexus and nitric oxide mediated motor response in normal human fundus

BACKGROUND AND AIMS

Achalasia is a disease of unknown aetiology. An immune mechanism has been suggested on the basis of previous morphological observations. The objective of this study was to test whether the serum of achalasia patients could reproduce the phenotype and functional changes that occur with disease progression in an ex vivo human model.

METHODS

Specimens of normal human fundus were maintained in culture in the presence of serum from patients with achalasia, gastro-oesophageal reflux disease (GORD), or healthy subjects (controls). Immunohistochemical detection of choline acetyltransferase (ChAT), neurone specific enolase (NSE), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), and substance P was carried out in whole mounts of gastric fundus myenteric plexus. In addition, the effects of achalasia serum on electrical field stimulation (EFS) induced contractions were measured in circular muscle preparations.

RESULTS

Serum from achalasia patients did not affect the number of myenteric neurones. Tissues incubated with serum from achalasia patients showed a decrease in the proportion of NOS (-26% of NSE positive neurones; p=0.016) and VIP (-54%; p=0.09) neurones, and a concomitant increase in ChAT neurones (+16%; p<0.001) compared with controls. In contrast, GORD serum did not modify the phenotype of myenteric neurones. Area under the curve of EFS induced relaxations (abolished by N-nitro-L-arginine methyl ester) was significantly decreased following incubation with serum from achalasia patients compared with controls (-7.6 (2.6) v -14.5 (5.0); p=0.036).

CONCLUSIONS

Serum from achalasia patients can induce phenotypic and functional changes which reproduce the characteristics of the disease. Further identification of putative seric factors and mechanisms involved could lead to the development of novel diagnostic and/or therapeutic strategies in achalasia.

Neural mechanisms involved in the inhibition of intestinal motility induced by intestinal electrical stimulation in conscious dogs

The effects and mechanisms of intestinal electrical stimulation (IES) with long pulses on intestinal motility were investigated in conscious dogs. Eighteen dogs were equipped with serosal electrodes and an intestinal cannula in the small bowel. The first experiment was designed to study the effect of one-channel IES on intestinal motility and the extent of this effect. The second experiment was conducted to study the effect of IES on intestinal motility and the involvement of neural pathway. The IES with long pulses significantly inhibited intestinal motility. Intestinal motility of the entire measured segment (40-220 cm distal to the stimulation electrodes) was inhibited by 60-74% with the single-channel IES with long pulses. Hexamethonium, guanethidine, phentolamine, propranolol partially, but not N(omega)-nitro-L-arginine (L-NNA), ondansetron and naloxone prevented the inhibitory effect of IES on intestinal motility. We conclude that single-channel IES inhibits intestinal motility within a distance of at least 2 m. This inhibitory effect induced by IES with long pulses is mediated via sympathetic but not nitrergic, serotoninergic 5-HT(3) and opiate pathway.

Roles of PACAP and PHI as inhibitory neurotransmitters in the circular muscle of mouse antrum

Mediators of neurogenic responses of the gastric antrum were studied in wild-type and pituitary adenylate cyclase-activating polypeptide (PACAP) -knockout (KO) mice. Electrical field stimulation (EFS) to the circular muscle strips of the wild-type mouse antrum induced a triphasic response; rapid transient relaxation and contraction, and sustained relaxation that was prolonged for an extended period after the end of EFS. The transient relaxation and contraction were completely inhibited by L-nitroarginine and atropine, respectively. The sustained relaxation was significantly inhibited by a PACAP receptor antagonist, PACAP(6-38). The antral strips prepared from PACAP-KO mice unexpectedly exhibited a tri-phasic response. However, the sustained relaxation was decreased to about one-half of that observed in wild-type mice. PACAP(6-38) inhibited EFS-induced sustained relaxation (33.5% of control) in PACAP-KO mice. Anti-peptide histidine isoleucine (PHI) serum partially (the 30% inhibition) or significantly (the 60% inhibition) inhibited the sustained relaxations in the wild-type and PACAP-KO mice, respectively. The immunoreactivities to the anti-PACAP and anti-PHI serums were found in myenteric ganglia of the mouse antrum. These results suggest that nitric oxide and acetylcholine mediate the transient relaxation and contraction, respectively, and that PACAP and PHI separately mediate the sustained relaxation in the antrum of the mouse stomach.

Gastric electrical stimulation inhibits postprandial antral tone partially via nitrergic pathway in conscious dogs

Gastric electrical stimulation (GES) has recently been explored as a therapeutic option for gastrointestinal motility disorders or obesity. The mechanism behind it is not fully elucidated. The aims of this study were to assess the effects of GES with different parameters on antral tone and to explore the involvement of the nitrergic pathway. Eight dogs equipped with a gastric cannula and one pair of serosal electrodes in the greater curvature 4 cm above the pylorus were studied on separate days. The study was composed of seven randomized sessions in the fed state [control, GES with different parameters, and GES plus neuronal nitric oxide synthase (nNOS) inhibitor]. Each session included three consecutive 30-min periods (baseline, GES, and recovery). GES was performed with long pulses or pulse trains. The antral volume was measured using an intragastric balloon connected with a barostat device. Behaviors of the dogs during each stimulation period were also noted. We found that 1) postprandial antral tone was reduced with GES with all tested parameter settings, reflected as a significant and substantial increase in antral volume ranging from 179 to 309%; 2) the inhibitory effect of GES on antral tone was partially blocked (decreased by 39.5%) with an nNOS inhibitor; and 3) mild symptoms were induced with GES and found to be correlated with the GES-induced increase in antral volume. We conclude that retrograde GES with long pulses or pulse trains inhibits antral tone, and this inhibitory effect is partially mediated via the nitrergic pathway. These results suggest that retrograde GES may have a therapeutic potential for obesity.

Decreased distribution of nitric oxide synthase and vasoactive intestinal polypeptide positive nerve cells in the sphincter of Oddi in humans with pancreatobiliary diseases

To better understand the relationship between innervation in the sphincter of Oddi and pancreatobiliary diseases, nerve cells which possess nitric oxide synthase (NOS) and/or vasoactive intestinal polypeptide (VIP) were studied immunohistochemically in the sphincter of Oddi and duodenum of humans. Specimens from autopsies included 11 cases with pancreatobiliary diseases and 7 cases without such diseases. An elaborate nerve network was revealed with an anti-S-100 antibody in the sphincter of Oddi and duodenum of all specimens. In the sphincter of Oddi of the control group, approximately 47% of the myenteric nerve cells were NOS positive, whereas 54% were VIP positive. Of the NOS positive nerve cells, 21% were also VIP positive. In contrast, 11% of the nerve cells in the sphincter of Oddi of the disease group were NOS positive while 32% were VIP positive. Within the duodenal myenteric plexus of the control group, 35% of all nerve cells were NOS positive while 40% was VIP positive; among them, 23% of the NOS positive cells were VIP positive. Similar results were observed in the duodenum of the disease group. These data indicate that abundant NOS and VIP positive innervation is present in the sphincter of Oddi and duodenum in humans. The lower proportion of NOS positive or VIP positive nerve cells of the disease group may suggest an inadequacy of the sphincter of Oddi to relax.

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.

Influence of sildenafil on gastric sensorimotor function in humans

After a meal, the proximal stomach relaxes probably through the activation of nitrergic neurons in the gastric wall. Nitric oxide-induced smooth muscle relaxation involves activation of soluble guanylate cyclase, with cGMP production, which is then degradated by phosphodiesterase-5 (PDE-5). The aim of this study was to investigate the effect of sildenafil, a selective PDE-5 inhibitor, on fasting and postprandial proximal gastric volume and on gastric emptying rates in humans. A gastric barostat was used to study gastric compliance and perception to isobaric distension in healthy subjects before and after placebo (n = 13) or sildenafil, 50 mg (n = 15). In 10 healthy subjects, two gastric barostat studies were performed in randomized order to study the effect of placebo or sildenafil on postprandial gastric relaxation. Similarly, solid and liquid gastric emptying rates were studied in 12 healthy subjects. Sildenafil significantly increased fasting intragastric volume (141 +/- 15 vs. 163 +/- 15 ml, P < 0.05) and volumes of first perception. Sildenafil induced a higher and prolonged gastric relaxation either at 30 min (357 +/- 38 vs. 253 +/- 42 ml, P < 0.05) or 60 min (348 +/- 49 vs. 247 +/- 38 ml, P < 0.05) after the meal. Sildenafil did not alter solid half-emptying time but significantly delayed liquid emptying (43 +/- 4 vs. 56 +/- 4 min, P < 0.01). In conclusion, sildenafil significantly increases postprandial gastric volume and slows liquid emptying rate, confirming that meal-induced accommodation in humans involves the activation of a nitrergic pathway. The effect of sildenafil on gastric fundus suggests a therapeutic potential for phosphodiesterase inhibitors in patients with impaired gastric accommodation.