Nitric oxide synthesis inhibition: the effect on rabbit pyloric muscle

Evaluating the molecular and genetic mechanisms underlying gut motility disorders

INTRODUCTION

Gastrointestinal (GI) motility disorders comprise a wide range of different diseases affecting the structural or functional integrity of the GI neuromusculature. Their clinical presentation and burden of disease depends on the predominant location and extent of gut involvement as well as the component of the gut neuromusculature affected.

AREAS COVERED

A comprehensive literature review was conducted using the PubMed and Medline databases to identify articles related to GI motility and functional disorders, published between 2016 and 2023. In this article, we highlight the current knowledge of molecular and genetic mechanisms underlying GI dysmotility, including disorders of gut-brain interaction, which involve both GI motor and sensory disturbance.

EXPERT OPINION

Although the pathophysiology and molecular mechanisms underlying many such disorders remain unclear, recent advances in the assessment of intestinal tissue samples, genetic testing with the application of 'omics' technologies and the use of animal models will provide better insights into disease pathogenesis as well as opportunities to improve therapy.

Infantile hypertrophic pyloric stenosis--genetics and syndromes

Infantile hypertrophic pyloric stenosis (IHPS) is a common condition in neonates that is characterized by an acquired narrowing of the pylorus. The aetiology of isolated IHPS is still largely unknown. Classic genetic studies have demonstrated an increased risk in families of affected infants. Several genetic studies in groups of individuals with isolated IHPS have identified chromosomal regions linked to the condition; however, these associations could usually not be confirmed in subsequent cohorts, suggesting considerable genetic heterogeneity. IHPS is associated with many clinical syndromes that have known causative mutations. Patients with syndromes associated with IHPS can be considered as having an extreme phenotype of IHPS and studying these patients will be instrumental in finding causes of isolated IHPS. Possible pathways in syndromic IHPS include: (neuro)muscular disorders; connective tissue disorders; metabolic disorders; intracellular signalling pathway disturbances; intercellular communication disturbances; ciliopathies; DNA-repair disturbances; transcription regulation disorders; MAPK-pathway disturbances; lymphatic abnormalities; and environmental factors. Future research should focus on linkage analysis and next-generation molecular techniques in well-defined families with multiple affected members. Studies will have an increased chance of success if detailed phenotyping is applied and if knowledge about the various possible causative pathways is used in evaluating results.

Hypertrophic pyloric stenosis and pulmonary hypertension in a neonate. A common mechanism?

Nitric oxide (NO) is an important mediator of biological functions. Absence or shortage of NO plays a role in the pathogenesis of both hypertrophic pyloric stenosis and persistent pulmonary hypertension. We present a neonate diagnosed with pulmonary hypertension after birth caused by meconium-aspiration syndrome eventually treated with extracorporal membrane oxygenation followed by hypertrophic pyloric stenosis for which a pyloromyotomy was performed. In conclusion, the association of pulmonary hypertension and pyloric stenosis has not been described before and may be explained by a lowered plasma concentration of arginine leading to deficient NO synthesis in the affected organ systems.

Effects and mechanism of changes of local neurotransmitters in rats' pylorus and bile reflux to the stomach with stress ulcer

Stress ulcer occurs primarily in severe conditions, with a high incidence and mortality in intensive care units. However, studies on the association between stress ulcer and bile reflux to the stomach with stress ulcer are still inconclusive. Therefore, our research aimed to determine whether or not bile reflux exists during stress ulcer and then to investigate the effects and mechanism of changes of pyloric local neurotransmitters on bile reflux in such circumstances so as to provide a new pathway for clinical intervention. Cold water immersion was used to copy the stress ulcer model of rats. Sixty-five adult Sprague-Dawley rats of either sex were randomly divided into three groups: the normal control group (n = 10), the stress group (n = 30), and the antagonist group (n = 25). The gastric ulcer index, pH, and bile acid of gastric juice were measured before and after stress. Radio Immunoassay Detection Kit and Biochemic Detection Kit were used to measure local contents of CGRP (calcitonin gene-related peptide) and nitric oxide, respectively, in rats' pylorus. The local contents of nitric oxide in rats' pylorus reached a maximum at 1 hr after stress. The bile acid and pH of gastric juice peaked at 2 hr after stress and the ulcer index peaked at 4 hr after stress. But the local contents of CGRP in rats' pylorus decreased to the minimum at 4 hr after stress. The bile acid and ulcer index in the L-NAME group were significantly lower than in the antagonist control group. However, the bile acid in the hCGRP8-37 group was less than in the antagonist control group. Compared with hCGRP8-37 group, there was a significant reduction in bile acid in the L-NAME group. There was a significant reduction in the ulcer index of the hCGRP8-37 group compared with the L-NAME group and the antagonist control group. There was a certain kind of positive correlation between nitric oxide in rats' pylorus and bile acid to the stomach, for nitric oxide could loosen the pyloric sphincter and increase the bile acid to the stomach. L-NAME might reduce the local nitric oxide contents in rats' pylorus so that bile acid to the stomach might be decreased, obviously with a looser tight pyloric sphincter. Meanwhile, the CGRP in rats' pylorus was negatively associated with the ulcer index, hence CGRP might protect gastric mucosa under stress conditions.

Effects of pyloric local CGRP and NO on bile reflux in rat stomach with stress ulcer

AIM: To investigate the effects of pyloric local CGRP and NO on bile reflux in rat stomach with stress ulcer.

METHODS: Rats stress ulcer model was established by cold water soaking. Sixty-five rats were divided into three groups: normal control group, the stress group and the antagonist group. The gastric ulcer index, pH and bile acid of gastric juice were measured before and after stress. The pyloric local CGRP was measured by a radioimmunoassay detection kit. The pyloric local nitric oxide was measured by a biochemic detection kit.

RESULTS: The pyloric local nitric oxide reached the climax at 1 hour after stress. The bile acid and pH of gastric juice reached the maximum at 2 hours after stress. The ulcer index did it at 4 hours after stress. But the pyloric local CGRP decreased to the minimum at 4 hours after stress. The bile acid and ulcer index in L-NAME group decreased significantly compared with those of h-CGRP8-37 group. However, the bile acid of hCGRP837 group was less than that of antagonist control group, which was weaker than that in L-NAME group.

CONCLUSION: There is a correlation between the pyloric local NO and bile acid in the stomach. L-NAME might reduce the pyloric local NO so that the bile acid in the stomach could be decreased obviously with less slacker pyloric sphincter. Meanwhile, the pyloric local CGRP has the negative correlation with ulcer index, for CGRP might protect gastric mucosa with stress ulcer.

Motor abnormality in the gastroduodenal junction in patients with infantile hypertrophic pyloric stenosis

BACKGROUND/PURPOSE

Periodic clusters of phasic pressure waves in the gastroduodenal junction (GDJ) have been seen in patients with infantile hypertrophic pyloric stenosis (IHPS). This study investigated the details of these pressure waves in relation to disturbed transpyloric flow in IHPS.

METHODS

Manometric study was performed in 11 IHPS patients before and after atropine therapy and 2 non-IHPS infants. Pressure changes in the GDJ were measured with an 8-channel sleeve or a 9-channel sidehole micromanometric assembly under fluoroscopic control for 2 hours.

RESULTS

Clusters of phasic pressure waves (365 +/- 42 mm Hg) associated with an increase in basal pressure (10 +/- 3 mm Hg) were intermittently observed in the GDJ in all IHPS patients. Similar observations were not made in the non-IHPS infants. Most antral pressure waves occurred simultaneously with those pressure waves in the GDJ in the IHPS patients. Atropine (0.01 mg/kg) transiently abolished the phasic and tonic pressure waves for 19 +/- 10 minutes. Significantly fewer phasic pressure waves were observed after atropine therapy.

CONCLUSIONS

Characteristic phasic and tonic contractile activity in the GDJ is uncoordinated with the antral contractions in IHPS patients. Such incoordination may be an important factor in the disturbed transpyloric flow in IHPS.

Nitric oxide synthase is absent in only a subset of cases of pyloric stenosis

PURPOSE

The aim of this study was to study nitric oxide synthase (NOS) immunohistochemistry in the pyloric muscle and establish the role of nitric oxide in pyloric stenosis.

METHODS

Pyloric muscle biopsy specimens were obtained from 20 patients with pyloric stenosis during pyloromyotomy. Ten control specimens without pyloric disease were obtained from autopsy performed less than 4 hours after death on age-matched babies who died of other causes. Tissues were fixed in 4% paraformaldehyde immediately. A monoclonal antibody against the neuronal form of NOS (bNOS) was used for immunohistochemistry.

RESULTS

Immunohistochemistry showed activity of bNOS in the control specimens and some pyloric stenosis specimens. This shows that NOS is present in the pylorus in normal cases as well as in a few cases of pyloric stenosis.

CONCLUSIONS

NOS deficiency leading to lack of locally available nitric oxide causes a failure of smooth muscle relaxation. This may account for the cause of pyloric stenosis in infants. However, this study shows that this is true probably only in a subset of cases. The etiology of pyloric stenosis may still be multifactorial. Further investigations are required regarding the etiology of pyloric stenosis. J Pediatr Surg 36:616-619.

Nitrergic and purinergic regulation of the rat pylorus

The role of nitric oxide (NO) and ATP in the regulation of nonadrenergic, noncholinergic (NANC) inhibitory transmission in the pylorus remains unclear. In the presence of atropine and guanethidine, electric field stimulation induced NANC relaxations in a frequency-dependent manner (1-20 Hz) in the rat pylorus. NANC relaxations were significantly inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M). P(2X) purinoceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 3 x 10(-5) M) and P(2Y) purinoceptor antagonist reactive blue 2 (2 x 10(-5) M) had no effect on NANC relaxations. However, the combined administration of L-NAME and PPADS, but not reactive blue 2, evoked greater inhibitory effects on NANC relaxation than that evoked by L-NAME alone. alpha-Chymotrypsin and vasoactive intestinal polypeptide antagonist did not affect NANC relaxations. ATP (10(-5)-10(-3) M) and P(2X) purinoceptor agonist alpha, beta-methyleneadenosine 5'-triphosphate (10(-7)-10(-5) M), but not P(2Y) purinoceptor agonist 2-methylthioadenosine 5'-triphosphate (10(-7)-10(-5) M), induced muscle relaxations in a dose-dependent manner, and relaxations were significantly reduced by PPADS and unaffected by TTX. These studies suggest that NO and ATP act in concert to mediate NANC relaxation of the rat pylorus. ATP-induced relaxation appears to be mediated by P(2X) purinoceptors located on smooth muscle cells.

Inhibitory neural pathway regulating gastric emptying in rats

The relaxation of the pylorus is one of the most important factors for promoting gastric emptying. However, the role of inhibitory neurotransmitters in the regulation of pyloric relaxation and gastric emptying remains unclear. In this study, we investigated the effects of NO biosynthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), and calcium dependent potassium channel blocker, apamin, on vagal stimulation-induced pyloric relaxation and gastric emptying in rats. Sodium nitroprusside (SNP), adenosine 5'-triphosphate (ATP), vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) caused pyloric relaxations in a dose dependent manner in vivo. Apamin (120 microg/kg) significantly reduced ATP and PACAP-induced pyloric relaxations without affecting SNP- or VIP-induced relaxations. Vagal stimulation (10 V, 1 ms, 1-20 Hz)-induced pyloric relaxation was significantly inhibited by L-NAME (10 mg/kg). The combined administration of L-NAME and apamin almost completely abolished vagal stimulation-induced pyloric relaxation. L-NAME and apamin significantly increased spontaneous contractions in the antrum, pylorus and duodenum. Increased motility index by L-NAME and apamin was significantly higher in the pylorus and duodenum, compared to that of antrum. L-NAME and apamin significantly delayed liquid gastric emptying. These results suggest that besides NO, probably ATP and PACAP, act as inhibitory neurotransmitters in the rat pylorus and regulate gastric emptying.

Characteristics of the muscularis mucosae in the acid-secreting region of the rabbit stomach

It has been suggested that muscularis mucosae excitation may augment gastric acid secretion, implying that this muscle should contract to secretagogues or stimulation of its motor innervation. The aim of this study was to characterize in vitro the responses of the muscularis mucosae in the rabbit gastric corpus to substances that modulate acid release and to intrinsic nerve stimulation. Muscularis mucosae from both fundic and antral ends of the corpus had identical mechanical properties, contracted to ACh, ADP, ATP, and histamine but relaxed to vasoactive intestinal polypeptide. Fundic but not antral muscularis mucosae contracted to bombesin and PGE2 and PGF2alpha, whereas adenosine, AMP, CCK, gastrin, secretin, and somatostatin were without effect on any preparation. In both regions electrical field stimulation evoked TTX-sensitive responses consisting of an atropine-resistant contraction followed by an NG-nitro-L-arginine methyl ester- and indomethacin-resistant relaxation. It is concluded from the regional variability in the pharmacological properties of the gastric muscularis mucosae that if its motor activity is linked to acid secretion this would be achieved by a neurally mediated relaxation rather than a paracrine- and/or endocrine-induced alteration in tone.