Postischemic intestinal motility in rat is inversely correlated to length of ischemia. An in vivo animal model

Risk factors for acute colonic pseudo-obstruction after caesarean section: A retrospective case-control study

BACKGROUND

Pregnancy and caesarean section are known to predispose to the development of acute colonic pseudo-obstruction (ACPO), a rare form of functional ileus of the distal large bowel. Pathogenesis of ACPO is likely influenced by pregnancy and childbirth and subsequent changes to hormonal, autonomic and metabolic physiology. Identifying pregnancy risk factors will assist with early identification, as the insidious onset postpartum often leads to delayed diagnosis and bowel ischaemia, perforation and sepsis.

AIMS

To establish pregnancy risk factors associated with the development of ACPO after caesarean section.

MATERIALS AND METHODS

A retrospective case-control study included 19 121 women undergoing caesarean between 1 January 2008 and 31 December 2016 at a tertiary referral hospital. Twenty-three cases of computerised tomography (CT)-diagnosed ACPO post-caesarean were identified from hospital medical records and imaging databases. Controls were matched for gestational and maternal age within one week of delivery with a ratio of 1:3.

RESULTS

The incidence of ACPO was one in 800 caesarean sections. ACPO was significantly more likely to occur in women who had been administered opioid analgesia in labour (odds ratio (OR) 4.67, P = 0.04), and a trend for increased estimated blood loss (OR 1.01, P = 0.01). There was no increased risk associated with emergency or elective caesarean classification, previous abdominal surgery, type of anaesthesia, duration of labour, oxytocin augmentation, intrapartum fever, hypertensive disorders, diabetes in pregnancy, antepartum haemorrhage, multiple gestation, fetal presentation or birthweight.

CONCLUSIONS

Risk factors for developing ACPO post-caesarean include opioid analgesia in labour and a trend for increased blood loss.

Tachykinin Antagonists Reverse Ischemia/Reperfusion Gastrointestinal Motility Impairment in Rats

BACKGROUND

Supraceliac aortic clamping and unclamping produces ischemia-reperfusion (I/R) injury of the splanchnic organs. The protective effects of tachykinin receptor antagonists, SR140333 (NK₁ receptor), SR48968 (NK₂ receptor), and SB222200 (NK₃ receptor), against I/R-induced inhibition of intestinal motility were tested in rats.

MATERIAL AND METHODS

The intestinal transit of Evans blue was measured in untreated rats and animals subjected to skin incision, I/R (1 h superior mesenteric artery occlusion followed by 24 h reperfusion) or sham operation. Surgical procedures were conducted under diethyl ether anesthesia.

RESULTS

The gastrointestinal transit has not been markedly affected in rats, which were anesthetized or subjected to skin incision in comparison with untreated animals. In contrast, a sham operation and I/R have significantly reduced the intestinal motility. Pretreatment with NK_1-3 blockers (SR140333 [3-30 μg/kg]; SR48968 [3-100 μg/kg]; and SB222200 [10-100 μg/kg]) reversed dose dependently the effects of I/R to the level observed after sham operation only. A combination of NK₁+NK₂+NK₃ inhibitors exerted an additive effect compared with NK₁ and NK₂ antagonists used as single agents. Similarly, combined NK₁+NK₂ were more effective than NK₂ alone. Sham operation and I/R have shifted the in vitro carbachol concentration-response curves to the right in comparison with untreated animals, a phenomenon partially reversed by NK₁-NK₃ pretreatment.

CONCLUSIONS

Single-agent and combined treatment with NK_1-3 antagonists markedly attenuated the gastrointestinal dysmotility evoked by I/R injury. The pretreatment with NK₃ blocker proved to be the most active in this experimental setting.

Role of glutamatergic neurotransmission in the enteric nervous system and brain-gut axis in health and disease

Several studies have been carried out in the last 30 years in the attempt to clarify the possible role of glutamate as a neurotransmitter/neuromodulator in the gastrointestinal tract. Such effort has provided immunohistochemical, biomolecular and functional data suggesting that the entire glutamatergic neurotransmitter machinery is present in the complex circuitries of the enteric nervous system (ENS), which participates to the local coordination of gastrointestinal functions. Glutamate is also involved in the regulation of the brain-gut axis, a bi-directional connection pathway between the central nervous system (CNS) and the gut. The neurotransmitter contributes to convey information, via afferent fibers, from the gut to the brain, and to send appropriate signals, via efferent fibers, from the brain to control gut secretion and motility. In analogy with the CNS, an increasing number of studies suggest that dysregulation of the enteric glutamatergic neurotransmitter machinery may lead to gastrointestinal dysfunctions. On the whole, this research field has opened the possibility to find new potential targets for development of drugs for the treatment of gastrointestinal diseases. The present review analyzes the more recent literature on enteric glutamatergic neurotransmission both in physiological and pathological conditions, such as gastroesophageal reflux, gastric acid hypersecretory diseases, inflammatory bowel disease, irritable bowel syndrome and intestinal ischemia/reperfusion injury.

Distinct subcellular localization of the neuronal marker HuC/D reveals hypoxia-induced damage in enteric neurons

BACKGROUND

Correct neuronal identification is essential to study neurons in health and disease. Although commonly used as pan-neuronal marker, HuC/D's expression pattern varies substantially between healthy and (patho)physiological conditions. This heterogenic labeling has received very little attention. We sought to investigate the subcellular HuC/D localization in enteric neurons in different conditions.

METHODS

The localization of neuronal RNA-binding proteins HuC/D was investigated by immunohistochemistry in the mouse myenteric plexus using different toxins and caustic agents. Preparations were also stained with Sox10 and glial fibrillary acidic protein (GFAP) antibodies to assess enteric glial cell appearance.

KEY RESULTS

Mechanically induced tissue damage, interference with the respiratory chain and oxygen (O2 ) deprivation increased nuclear HuC/D immunoreactivity. This effect was paralleled by a distortion of the GFAP-labeled glial network along with a loss of Sox10 expression and coincided with the activation of a non-apoptotic genetic program. Chemically induced damage and specific noxious stimuli did not induce a change in HuC/D immunoreactivity, supporting the specific nature of the nuclear HuC/D localization.

CONCLUSIONS & INFERENCES

HuC/D is not merely a pan-neuronal marker but its subcellular localization also reflects the condition of a neuron at the time of fixation. The functional meaning of this change in HuC/D localization is not entirely clear, but disturbance in O2 supply in combination with the support of enteric glial cells seems to play a crucial role. The molecular consequence of changes in HuC/D expression needs to be further investigated.

Febuxostat improves the local and remote organ changes induced by intestinal ischemia/reperfusion in rats

BACKGROUND

Xanthine oxidase has been implicated in the pathogenesis of a wide spectrum of diseases, and is thought to be the most important source of oxygen-free radicals and cell damage during re-oxygenation of hypoxic tissues.

AIMS

The present study was undertaken to demonstrate whether febuxostat is superior to allopurinol in prevention of the local and remote harmful effects of small intestinal ischemia/reperfusion injury in rats.

METHODS

Intestinal ischemia was induced by superior mesenteric artery ligation. The rats were assigned to five groups: the sham control; the intestinal ischemia/reperfusion; the allopurinol; and the febuxostat 5 and 10 mg/kg pretreated ischemia/reperfusion groups. Treatment was administered from 7 days before ischemia induction. After the reperfusion, the serum and tissues were obtained for biochemical, pharmacological, and histological studies.

RESULTS

Intestinal reperfusion led to an elevation in the serum levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α, malondialdehyde, and xanthine oxidase as well as intestinal myeloperoxidase, malonadialdehyde, and xanthine oxidase/xanthine dehydrogenase activity. Furthermore, the ischemia/reperfusion induced a reduction in the contractile responsiveness to acetylcholine. These changes were significantly regulated by the pretreatment with febuxostat compared to allopurinol. The degree of pathological impairment in the intestinal mucosa, liver, and lung tissues were lighter in the pretreated groups.

CONCLUSIONS

Febuxostat may offer advantages over allopurinol in lessening local intestinal injury as well as remote hepatic and lung injuries induced by small intestinal ischemia/reperfusion.

Role of neuronal and inducible nitric oxide synthases in the guinea pig ileum myenteric plexus during in vitro ischemia and reperfusion

BACKGROUND

Intestinal ischemia and reperfusion (I/R) injury leads to abnormalities in motility, namely delay of transit, caused by damage to myenteric neurons. Alterations of the nitrergic transmission may occur in these conditions. This study investigated whether an in vitro I/R injury may affect nitric oxide (NO) production from the myenteric plexus of the guinea pig ileum and which NO synthase (NOS) isoform is involved.

METHODS

The distribution of the neuronal (n) and inducible (i) NOS was determined by immunohistochemistry during 60 min of glucose/oxygen deprivation (in vitro ischemia) followed by 60 min of reperfusion. The protein and mRNA levels of nNOS and iNOS were investigated by Western-immunoblotting and real time RT-PCR, respectively. NO levels were quantified as nitrite/nitrate.

KEY RESULTS

After in vitro I/R the proportion of nNOS-expressing neurons and protein levels remained unchanged. nNOS mRNA levels increased 60 min after inducing ischemia and in the following 5 min of reperfusion. iNOS-immunoreactive neurons, protein and mRNA levels were up-regulated during the whole I/R period. A significant increase of nitrite/nitrate levels was observed in the first 5 min after inducing I/R and was significantly reduced by N(ω) -propyl-l-arginine and 1400 W, selective inhibitors of nNOS and iNOS, respectively.

CONCLUSIONS & INFERENCES

Our data demonstrate that both iNOS and nNOS represent sources for NO overproduction in ileal myenteric plexus during I/R, although iNOS undergoes more consistent changes suggesting a more relevant role for this isoform in the alterations occurring in myenteric neurons following I/R.

Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow

BACKGROUND

The prevalence of exercise-induced gastrointestinal (GI) symptoms has been reported up to 70%. The pathophysiology largely remains unknown.

AIM

To review the physiological and pathophysiological changes of the GI-tract during physical exercise and the management of the most common gastrointestinal symptoms.

METHODS

Search of the literature published in the English and Dutch languages using the Pubmed database to review the literature that focused on the relation between splanchnic blood flow (SBF), development of ischaemia, postischaemic endotoxinemia and motility.

RESULTS

During physical exercise, the increased activity of the sympathetic nervous system (SNS) redistributes blood flow from the splanchnic organs to the working muscles. With prolonged duration and/or intensity, the SBF may be decreased by 80% or more. Most studies point in the direction of increased SNS-activity as central driving force for reduction in SBF. A severely reduced SBF may frequently cause GI ischaemia. GI-ischaemia combined with reduced vagal activity probably triggers changes in GI-motility and GI absorption derangements. GI-symptoms during physical exercise may be prevented by lowering the exercise intensity, preventing dehydration and avoiding the ingestion of hypertonic fluids.

CONCLUSIONS

Literature on the pathophysiology of exercise-induced GI-symptoms is scarce. Increased sympathetic nervous system activity and decreased splanchnic blood flow during physical exercise seems to be the key factor in the pathogenesis of exercise-induced GI-symptoms, and this should be the target for symptom reduction.

The involvement of nitric oxide synthase neurons in enteric neuropathies

Nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS) is a transmitter of inhibitory neurons supplying the muscle of the gastrointestinal tract. Transmission from these neurons is necessary for sphincter relaxation that allows the passage of gut contents, and also for relaxation of muscle during propulsive activity in the colon. There are deficiencies of transmission from NOS neurons to the lower esophageal sphincter in esophageal achalasia, to the pyloric sphincter in hypertrophic pyloric stenosis and to the internal anal sphincter in colonic achalasia. Deficits in NOS neurons are observed in two disorders in which colonic propulsion fails, Hirschsprung's disease and Chagas' disease. In addition, damage to NOS neurons occurs when there is stress to cells, in diabetes, resulting in gastroparesis, and following ischemia and reperfusion. A number of factors may contribute to the propensity of NOS neurons to be involved in enteric neuropathies. One of these is the failure of the neurons to maintain Ca(2+) homeostasis. In neurons in general, stress can increase cytoplasmic Ca(2+), causing a Ca(2+) toxicity. NOS neurons face the additional problem that NOS is activated by Ca(2+). This is hypothesized to produce an excess of NO, whose free radical properties can cause cell damage, which is exacerbated by peroxynitrite formed when NO reacts with oxygen free radicals.

Application of heme oxygenase-1, carbon monoxide and biliverdin for the prevention of intestinal ischemia/reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury occurs frequently in a variety of clinical settings, including mesenteric artery occlusion, abdominal aneurism surgery, trauma, shock, and small intestinal transplantation, and is associated with substantial morbidity and mortality. Although the exact mechanisms involved in the pathogenesis of intestinal I/R injury have not been fully elucidated, it is generally believed that polymorphonuclear neutrophils, pro-inflammatory cytokines, and mediators generated in the setting of oxidative stress, such as reactive oxygen species (ROS), play important roles. Heme oxygenase (HO) is the rate-limiting enzyme that catalyzes the degradation of heme into equimolar quantities of biliverdin and carbon monoxide (CO), while the central iron is released. An inducible form of HO (HO-1), biliverdin, and CO, have been shown to possess generalized endogenous anti-inflammatory activities and provide protection against intestinal I/R injury. Further, recent observations have demonstrated that exogenous HO-1 expression, as well as exogenously administered CO and biliverdin, have potent cytoprotective effects on intestinal I/R injury as well. Here, we summarize the currently available data regarding the role of the HO system in the prevention intestinal I/R injury.

Protein kinase C modulates NMDA receptors in the myenteric plexus of the guinea pig ileum during in vitro ischemia and reperfusion

BACKGROUND

Ischemic episodes lead to profound functional and structural alterations of the gastrointestinal tract which may contribute to disorders of intestinal motility. Enhancement of glutamate overflow and the consequent activation of NMDA (N-methyl-D-aspartate) receptors may participate to such changes by modulating different enteric neurotransmitter systems, including cholinergic motor pathways.

METHODS

The molecular mechanism/s underlying activation of NMDA receptors in the guinea pig ileum were investigated after glucose/oxygen deprivation (in vitro ischemia) and during reperfusion.

KEY RESULTS

The number of ileal myenteric neurons positive for NR1, the functional subunit of NMDA receptors, and its mRNA levels were unchanged after in vitro ischemia/reperfusion. In these conditions, the protein levels of NR1, and of its phosphorylated form by protein kinase C (PKC), significantly increased in myenteric neurons, whereas, the levels of NR1 phosphorylated by protein kinase A (PKA) did not change, with respect to control values. Spontaneous glutamate overflow increased during in vitro ischemia/reperfusion. In these conditions, the NMDA receptor antagonists, D(-)-2-amino-5-phosphonopentanoic acid [(D)-AP5] (10 μmol L(-1)) and 5,7-dichlorokynurenic acid (5,7-diClKyn acid) (10 μmol L(-1)) and the PKC antagonist, chelerythrine (1 μmol L(-1)), but not the PKA antagonist, H-89 (1 μmol L(-1)), were able to significantly depress the increased glutamate efflux.

CONCLUSIONS & INFERENCES

The present data suggest that in the guinea pig ileum during in vitro ischemia/reperfusion, NR1 protein levels increase. Such event may rely upon posttranscriptional events involving NR1 phosphorylation by PKC. Increased NR1 levels may, at least in part, explain the ability of NMDA receptors to modulate a positive feedback on ischemia/reperfusion-induced glutamate overflow.

Damaging effects of ischemia/reperfusion on intestinal muscle

Periods of ischemia followed by restoration of blood flow cause ischemia/reperfusion (I/R) injury. In the intestine, I/R damage to the mucosa and neurons is prominent. Functionally, abnormalities occur in motility, most conspicuously a slowing of transit, possibly as a consequence of damage to neurons and/or muscle. Here, we describe degenerative and regenerative changes that have not been previously reported in intestinal muscle. The mouse small intestine was made ischemic for 1 h, followed by re-perfusion for 1 h to 7 days. The tissues were examined histologically, after hematoxylin/eosin and Masson's trichrome staining, and by myeloperoxidase histochemistry to detect inflammatory reactions to I/R. Histological analysis revealed changes in the mucosa, muscle, and neurons. The mucosa was severely but transiently damaged. The mucosal surface was sloughed off at 1-3 h, but re-epithelialization occurred by 12 h, and the epithelium appeared healthy by 1-2 days. Longitudinal muscle degeneration was followed by regeneration, but little effect on the circular muscle was noted. The first signs of muscle change were apparent at 3-12 h, and by 1 and 2 days, extensive degeneration within the muscle was observed, which included clear cytoplasm, pyknotic nuclei, and apoptotic bodies. The muscle recovered quickly and appeared normal at 7 days. Histological evidence of neuronal damage was apparent at 1-7 days. Neutrophils were not present in the muscle layers and were infrequent in the mucosa. However, they were often seen in the longitudinal muscle at 1-3 days and were also present in the circular muscle. Neutrophil numbers increased in the mucosa in both I/R and sham-operated animals and remained elevated from 1 h to 7 days. We conclude that I/R causes severe longitudinal muscle damage, which might contribute to the long-term motility deficits observed after I/R injury to the intestine.

Delayed gastric emptying and disruption of the interstitial cells of Cajal network after gastric ischaemia and reperfusion

BACKGROUND

Gastrointestinal tract is one of the most susceptible organ systems to ischaemia. Not only mucosal injury but also alterations of the intestinal motility and loss of interstitial cells of Cajal (ICC) have been reported in response to ischaemia and reperfusion (I/R). However, there are few reports on the changes in the gastric motility after gastric I/R. The present study was designed to investigate the alterations in gastric emptying, the ICC and enteric nerves that regulate smooth muscle function in response to gastric I/R.

METHODS

Seven-week-old male Wistar rats were exposed to gastric I/R, and the gastric emptying rates at 12 and 48 h after I/R were evaluated by the phenol red method. Expressions of gene product of c-kit receptor tyrosine kinase (c-Kit), a marker of ICC, and of neuronal proteins were also examined.

KEY RESULTS

Gastric emptying was transiently delayed at 12 h after I/R, but returned to normal by 48 h. Expression of c-Kit protein as assessed by Western blotting and immunofluorescent staining of the smooth muscle layer, as well as expression of the mRNA of stem cell factor, the ligand for c-Kit, were reduced at both 12 and 48 h after I/R. The expression of neuronal nitric oxide synthase (nNOS) protein as assessed by Western blotting and immunofluorescent staining was also decreased at 12 h after I/R, but was restored to normal by 48 h.

CONCLUSIONS & INFERENCES

Gastric I/R evokes transient gastroparesis with delayed gastric emptying, associated with disruption of the ICC network and nNOS-positive neurons.

The reactions of specific neuron types to intestinal ischemia in the guinea pig enteric nervous system

Damage following ischemia and reperfusion (I/R) is common in the intestine and can be caused during abdominal surgery, in several disease states and following intestinal transplantation. Most studies have concentrated on damage to the mucosa, although published evidence also points to effects on neurons. Moreover, alterations of neuronally controlled functions of the intestine persist after I/R. The present study was designed to investigate the time course of damage to neurons and the selectivity of the effect of I/R damage for specific types of enteric neurons. A branch of the superior mesenteric artery supplying the distal ileum of anesthetised guinea pigs was occluded for 1 h and the animals were allowed to recover for 2 h to 4 weeks before tissue was taken for the immunohistochemical localization of markers of specific neuron types in tissues from sham and I/R animals. The dendrites of neurons with nitric oxide synthase (NOS) immunoreactivity, which are inhibitory motor neurons and interneurons, were distorted and swollen by 24 h after I/R and remained enlarged up to 28 days. The total neuron profile areas (cell body plus dendrites) increased by 25%, but the sizes of cell bodies did not change significantly. Neurons of type II morphology (intrinsic primary afferent neurons), revealed by NeuN immunoreactivity, were transiently reduced in cell size, at 24 h and 7 days. These neurons also showed signs of minor cell surface blebbing. Calretinin neurons, many of which are excitatory motor neurons, were unaffected. Thus, this study revealed a selective damage to NOS neurons that was observed at 24 h and persisted up to 4 weeks, without a significant change in the relative numbers of NOS neurons.

Tempol reduces bacterial translocation after ischemia/reperfusion injury in a rat model of superior mesenteric artery occlusion

PURPOSE

We investigated whether Tempol, a water-soluble antioxidant, prevents the harmful effects of superior mesenteric ischemia/reperfusion on intestinal tissues in rats.

METHODS

The rats were divided into three groups of 10. In group 1, the superior mesenteric artery (SMA) was isolated but not occluded, and in groups 2 and 3 the superior mesenteric artery was occluded for 60 min. After that, the clamp was removed and reperfusion began. In group 3, 5 min before the start of reperfusion, a bolus dose of 30 mg/kg Tempol was administered intravenously and continued at a dose of 30 mg/kg for 60 min. All animals were euthanized after 24 h and tissue samples were collected for analysis.

RESULTS

There was a significant increase in myeloperoxidase activity, malondialdehyde levels, and the incidence of bacterial translocation in group 2, with a decrease in glutathione levels. These parameters were found to be normalized in group 3. The intestinal mucosal injury score in group 2 was significantly higher than those in groups 1 and 3.

CONCLUSION

Tempol prevents bacterial translocation while precluding the harmful effects of ischemia/reperfusion injury on intestinal tissues in a rat model of superior mesenteric artery occlusion.

Changes in intestinal motility and in the myenteric plexus in a rat model of intestinal ischemia-reperfusion

BACKGROUND/PURPOSE

Early histologic changes induced by intestinal ischemia-reperfusion injury (IIRI) have been extensively studied using animal models. However, information regarding late effects on intestinal motility is lacking. The aim of this study was to investigate the late effects of IIRI on myenteric plexus histology and intestinal motility.

MATERIALS AND METHODS

Thirty-two postweaning male rats weighing between 58 and 103 g were divided randomly into 4 groups: Control (unoperated), Sham (celiotomy), 30-minute ischemia (celiotomy and superior mesenteric artery ischemia for 30 minutes), and 45-minute ischemia (celiotomy and superior mesenteric artery ischemia for 45 minutes). Postoperative intestinal motility was assessed by weighing total fecal output for 24 hours on the 3rd, 7th, 14th, and 21st day after surgery. Segments of duodenum, jejunum, and ileum were examined at light microscopy for changes in the myenteric plexus.

RESULTS

Three weeks after IIRI, the ganglion cells from the myenteric plexus appeared in light microscopy, spongy or foamy, containing many vacuoles in their cytoplasm. The neuronal nucleus became irregular, with degenerative signs. These alterations did not occur among animals from the control or sham groups. Although the animals of the 45-minute ischemia group showed a significant drop in fecal output in the 21st postoperative day, this appeared to have no effect on weight gain.

CONCLUSIONS

The results suggest that intestinal ischemia-reperfusion causes late neuronal damage. These changes resulted in alterations of intestinal motility, which, within the conditions of the present study, had no repercussion on general weight gain.

Intestinal Ischemia/Reperfusion Injury Aggravates Talc-Induced Adhesions in Rats

BACKGROUND

Postoperative intraperitoneal adhesions are the leading cause of intestinal obstruction, but the underlying mechanisms remain incompletely understood. The aim of the current study was to investigate the involvement of intestinal ischemia/reperfusion (I/R) injury in adhesion formation in rats.

MATERIALS AND METHODS

Rats were subjected to either a dusting of talc (15 mg/rat) over the entire small intestine or ischemia induced by clamping the superior mesenteric artery (SMA) for 30 min followed by reperfusion with or without talc dusting. On postoperative days 4, 7, and 14, the scores, lengths, and incidence of adhesions were evaluated. In addition, the contractile force of the jejunal muscle was measured at 0, 24, 48, and 96 h after the treatments using organ bath techniques under bethanechol-stimulated conditions.

RESULTS

Talc induced mild adhesions in rats. Although I/R injury alone did not produce adhesions, it markedly aggravated the talc-induced adhesions, with higher scores and longer adhesions on postoperative days 4, 7, and 14. In addition, I/R injury caused 75-88% suppression of the circular muscle contractile force and 35-52% suppression of the longitudinal muscle contractile force at 24 h after SMA occlusion. However, talc did not affect the contractions.

CONCLUSIONS

Intestinal I/R injury aggravated the talc-induced adhesions, and this consequence might be due to the functional suppression of jejunal muscle contractions. This finding suggests that intestinal ischemia is an important factor in the etiology of postoperative adhesions.

Protective effect of proteinase-activated receptor 2 activation on motility impairment and tissue damage induced by intestinal ischemia/reperfusion in rodents

We hypothesized that proteinase-activated receptor-2 (PAR(2)) modulates intestinal injuries induced by ischemia/reperfusion. Ischemia (1 hour) plus reperfusion (6 hours) significantly delayed gastrointestinal transit (GIT) compared with sham operation. Intraduodenal injection of PAR(2)-activating peptide SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion but not in sham-operated rats. GIT was significantly delayed in ischemia/reperfusion and sham-operated PAR(2)(-/-) mice compared with PAR(2)(+/+). SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion in PAR(2)(+/+) but not in PAR(2)(-/-) mice. Prevention of mast cell degranulation with cromolyn, ablation of visceral afferents with capsaicin, and antagonism of calcitonin gene-related peptide (CGRP) and neurokinin-1 receptors with CGRP(8-37) and RP67580, respectively, abolished the SLIGRL-NH(2)-induced stimulatory effect on transit in ischemia/reperfusion. Tissue damage was significantly reduced by SLIGRL-NH(2); this effect was not observed in cromolyn-, capsaicin-, or RP67580-treated rats but was detected following CGRP(8-37). Intestinal PAR(2) mRNA levels were not affected by SLIGRL-NH(2) in ischemia/reperfusion. We propose that PAR(2) modulates GIT and tissue damage in intestinal ischemia/reperfusion by a mechanism dependent on mast cells and visceral afferents. PAR(2) effect on transit might be mediated by CGRP and substance P, whereas the effect on tissue damage appears to involve substance P but not CGRP. PAR(2) might be a signaling system in the neuroimmune communication in intestinal ischemia/reperfusion.

Interstitial cells of Cajal in dysmotility in intestinal ischemia and reperfusion injury in rats

BACKGROUND

Intestinal ischemia and reperfusion (I/R) injury is an obligatory occurrence in small bowel transplantation. I/R may impair the normal gastrointestinal motility. Interstitial cells of Cajal (ICC) are known as pacemaker cells in the gastrointestinal tract. The aim of this study was to assess the role of ICC in the gastrointestinal motility in a rat model of I/R injury.

MATERIALS AND METHODS

Wistar rats were subjected to 30- or 80-min intestinal ischemia by occluding the mesenteric vessels followed by reperfusion. Small intestinal segments were resected at 12 h or 4 days. The spontaneous mechanical activity was evaluated by organ bath technique. Immunopositivity of c-Kit and PGP9.5 at the level of the myenteric plexus was evaluated as markers of ICC and enteric nerves, respectively.

RESULTS

In the bowel segment with 80-min ischemia followed by 12-h reperfusion, muscles showed a 25% reduction (P < 0.05) in the frequency of contractions compared to that with 30-min ischemia followed by 12-h reperfusion, whereas amplitude of contractions was not significantly different. This change was associated with a 70% decrease (P < 0.01) of c-Kit immunopositivity. These changes of intestinal motility pattern and distribution of c-Kit-positive cells were both recovered from 80-min ischemia followed by 4 days reperfusion. In contrast, the immunopositivity of PGP9.5 was not affected in any I/R injury group.

CONCLUSIONS

Transient functional changes in ICC were induced by prolonged I/R injury but they recovered after 4 days, suggesting a central role of ICC in both disrupting and restoring the normal gastrointestinal motility in I/R injury.

Altered responsiveness of the guinea-pig isolated ileum to smooth muscle stimulants and to electrical stimulation after in situ ischemia

1. We evaluated changes in contractility of the guinea-pig isolated ileum, using intact segments and myenteric plexus-longitudinal muscle (MPLM) preparations, after several times (5-160 min) of ischemia in situ. 2. Intestinal ischemia was produced by clamping the superior mesenteric artery. Ischemic and nonischemic segments, obtained from the same guinea-pig, were mounted in organ baths containing Krebs-bicarbonate (K-B) solution, maintained at 37 degrees C and gassed with 95% O2/5% CO2. The preparations were allowed to equilibrate for 60 min under continuous superfusion of warm K-B solution and then electrically stimulated at 40 V (0.3 Hz, 3.0 ms). Thereafter, complete noncumulative concentration-response curves were constructed for acetylcholine (ACh), histamine (HIS), potassium chloride (KCl), and barium chloride (BaCl2). Mean Emax (maximal response) values were calculated for each drug. 3. Our study shows that alterations of chemically and electrically evoked contractions are dependent on ischemic periods. It also demonstrates that contractile responses of ischemic tissues to neurogenic stimulation decreases earlier and to a significantly greater extent than the non-nerve mediated responses of the intestinal smooth muscle. Contractile responses to smooth muscle stimulants were all similarly affected by ischemia. Electron microscopy images indicated necrotic neuronal death. The decrease in reactivity of ischemic tissues to electrical stimulation was ameliorated by dexrazoxane, an antioxidant agent. 4. We consider the guinea-pig isolated ileum as a useful model system to study the processes involved in neuronal ischemia, and we propose that the reduction in maximal responses to electrical stimulation is a useful parameter to study neuroprotection.

Involvement of glutamate receptors of the NMDA type in the modulation of acetylcholine and glutamate overflow from the guinea pig ileum during in vitro hypoxia and hypoglycaemia

The involvement of NMDA glutamate receptors in the effects of glucose/oxygen deprivation (in vitro ischaemia) on spontaneous endogenous acetylcholine and glutamate overflow from the guinea pig ileum was studied. Neurotransmitter overflow was measured by HPLC. Deprivation of glucose in the medium slightly reduced acetylcholine overflow, and did not significantly influence glutamate overflow. During oxygen deprivation and glucose/oxygen deprivation, acetylcholine overflow augmented with a biphasic modality: an early peak was followed by a long lasting increase, whereas glutamate overflow increased with a rapid and sustained modality. The effects of glucose/oxygen deprivation on both acetylcholine and glutamate overflow were abolished after reperfusion with normal oxygenated medium. Acetylcholine and glutamate overflow induced by glucose/oxygen deprivation were significantly reduced in the absence of external Ca(2+) as well as by the addition of the mitochondrial Na(+)-Ca(2+) exchanger blocker, CGP 37157, and of the endoplasmic reticulum Ca(2+)/ATPase blocker, thapsigargin. +/-AP5, an NMDA receptor antagonist, and 5,7-diCl-kynurenic acid, an antagonist of the glycine site associated to NMDA receptor, markedly depressed glucose/oxygen deprivation-induced acetylcholine and glutamate overflow as well. Our results suggest that in vitro simulated ischaemia evokes acetylcholine and glutamate overflow from the guinea pig ileum, which is partly linked to an increase in intracellular Ca(2+) concentration dependent on both Ca(2+) influx from the extracellular space and Ca(2+) mobilization from the endoplasmic reticulum and mitochondrial stores. During glucose/oxygen deprivation, ionotropic glutamate receptors of the NMDA type exert both a positive feedback modulation of glutamate output and contribute to increased acetylcholine overflow.

Effect of N-methyl-d-aspartate receptor blockade on neuronal plasticity and gastrointestinal transit delay induced by ischemia/reperfusion in rats

Intestinal ischemia impairs gastrointestinal motility. The aims of this study were to investigate the effect of intestinal ischemia on gastrointestinal transit and on the expression of enteric transmitters in the rat, and whether the glutamate N-methyl-d-aspartate receptors influence these effects. Ischemia (1 h), induced by occluding the superior mesenteric artery, was followed by 0 or 24 h of reperfusion. Normal and sham-operated rats served as controls. Serosal blood flow was measured with laser Doppler flow meter. Gastrointestinal transit was measured as time of appearance of a marker in fecal pellets. Immunohistochemistry was used to evaluate the number of neurons immunoreactive for neuronal nitric oxide synthase (NOS) or vasoactive intestinal polypeptide and the density of substance P immunoreactive fibers in the myenteric plexus. The N-methyl-d-aspartate receptors antagonist, (+)-5-methyl-10,11-dihydro-5HT-[a,b] cyclohepten-5,10-imine (MK-801) (1 mg/kg i.v.) or the NOS inhibitor, N-nitro-l-arginine (10 mg/kg i.v.) was administered prior to ischemia. Serosal blood flow was decreased by 70% during ischemia, but it was not altered in sham-operated rats. Gastrointestinal transit was significantly prolonged in ischemic/reperfused rats compared with controls. There was a significant increase in the number of vasoactive intestinal polypeptide and neuronal nitric oxide synthase immunoreactive neurons, and a marked decrease of substance P immunoreactive fibers in ischemia followed by 24 h of reperfusion animals compared with controls. These alterations were not observed in ischemia without reperfusion. A significant delay of gastrointestinal transit and increase of vasoactive intestinal polypeptide neurons were also observed in sham-operated rats. The changes in transmitter expression and gastrointestinal transit in ischemic/reperfused rats were prevented by pre-treatment with the NOS inhibitor, N-nitro-l-arginine or the N-methyl-d-aspartate receptors antagonist, MK-801. This study suggests an involvement of the glutamatergic system and its interaction with nitric oxide in intestinal ischemia/reperfusion. Ischemia/reperfusion might induce local release of glutamate that activates N-methyl-d-aspartate receptors leading to increased production of nitric oxide and adaptive changes in enteric transmitters that might contribute to gastrointestinal dysmotility.

Resuscitation-induced gut edema and intestinal dysfunction

BACKGROUND

Mesenteric venous hypertension and subsequent gut edema play a pivotal role in the development of intra-abdominal hypertension. Although gut edema is one cause of intra-abdominal hypertension, its impact on gut function is unknown. The purpose of this study was to create a model of acute hydrostatic gut edema and to evaluate its effect on gut motility and barrier function.

METHODS

The first study, group A, evaluated the effect of gut edema on transit over time using 20 mL/kg 0.9% saline. The second study, group B, focused on the 12-hour time period using 80 mL/kg 0.9% saline. Rats were randomized to superior mesenteric vein partial occlusion (venous hypertension) or sham surgery. At 6, 12, and 24 hours, group A underwent intestinal transit and tissue water weight measurements. At 12 hours, group B underwent tissue water, transit, ileal permeability and resistance, lactate and myeloperoxidase activity, and mucosal injury measurements.

RESULTS

Venous hypertension with fluid resuscitation caused acute hydrostatic gut edema, delayed intestinal transit, increased mucosal permeability to macromolecules, and decreased tissue resistance over time. Mucosal injury was minimal in mesenteric venous hypertension.

CONCLUSION

Acute mesenteric venous hypertension and resuscitation-induced gut edema, in the absence of ischemia/reperfusion injury, is associated with delayed intestinal transit and altered gut barrier function.

Structural and neuronal changes in rat ileum after ischemia with reperfusion

Intestinal ischemia/reperfusion (I/R) is of profound importance in many clinical situations. The present study investigates short- and long-term changes, in particular in enteric neurons, but also with respect to the presence of eosinophilic leukocytes, goblet cells, and mast cells in the intestinal wall using an experimental model for intestinal I/R. Structural changes were also examined. Specimens from untreated, sham-operated, and ischemia (60 min)/reperfusion (1 hr-10 weeks) rat ileum were studied using histochemistry and morphometry. After I/R a marked acidophilia was noted in both submucous and myenteric neurons. This preceded a loss of myenteric, but not submucous, neurons. A low number of acidophilic neurons was noted also in sham-operated segments. Eosinophils and mast cells gradually increased after I/R and were notably found in smooth muscle and myenteric ganglia. Structural changes included mucosal shedding followed by restitution with an epithelium transiently containing a high number of goblet cells and a marked thickening of the muscular layers.

Pseudo-obstruction in the critically ill

Intestinal pseudo-obstruction is defined as a clinical syndrome characterized by impairment of intestinal propulsion, which may resemble intestinal obstruction, in the absence of a mechanical cause. It may involve the small and/or the large bowel, and may present in acute, subacute or chronic forms. We have performed a systematic review of acute pseudo-obstruction, also referred to as Ogilvie's syndrome in the literature, and focused on proposed mechanisms, manifestations and management of post-surgery and critically ill patients who suffer from one or more underlying clinical conditions. The hallmark of the syndrome is massive intestinal distension, which is detected on clinical inspection and plain abdominal radiography. The underlying pathophysiological mechanisms are not fully understood. Therefore, treatment focuses on preventing intestinal perforation, which is associated with an average 21% mortality rate.

Pseudo-obstruction in the critically ill

Intestinal pseudo-obstruction is defined as a clinical syndrome characterized by impairment of intestinal propulsion, which may resemble intestinal obstruction, in the absence of a mechanical cause. It may involve the small and/or the large bowel, and may present in acute, subacute or chronic forms. We have performed a systematic review of acute pseudo-obstruction, also referred to as Ogilvie's syndrome in the literature, and focused on proposed mechanisms, manifestations and management of post-surgery and critically ill patients who suffer from one or more underlying clinical conditions. The hallmark of the syndrome is massive intestinal distension, which is detected on clinical inspection and plain abdominal radiography. The underlying pathophysiological mechanisms are not fully understood. Therefore, treatment focuses on preventing intestinal perforation, which is associated with an average 21% mortality rate.

Manejo clínico de la seudoobstrucción aguda de colon en el enfermo hospitalizado: revisión sistemática de la bibliografía

Intestinal pseudoobstruction is a clinical syndrome characterized by impairment of intestinal propulsion, which may resemble intestinal obstruction, in the absence of a mechanical cause. It usually affects the colon but the small intestine may also be involved, and may present in acute, subacute or chronic forms. We have performed a systematic review of the acute form of pseudoobstruction, also referred to as Ogilvie's syndrome. We discuss proposed pathophysiological mechanisms, manifestations and management of this clinical condition in post-surgery and critically ill patients. The hallmark of the syndrome is massive intestinal distension, which is detected on clinical inspection and plain abdominal radiography. The underlying pathophysiological mechanisms are not fully understood. Therefore, treatment has focussed on preventing intestinal perforation, which is associated with a 21% mortality rate.

Alterations of intestinal motor responsiveness in a model of mild mesenteric ischemia/reperfusion in rats

In this study we investigate the changes in intestinal motor responsiveness after mild mesenteric ischemia/reperfusion in anaesthetized rats. Motor responsiveness to pharmacological/electrical stimulation was studied in isolated ileum excised from sham-operated rats or animals which underwent occlusion of superior mesenteric artery (1 h) plus interruption of collateral blood flow and reperfusion for 0, 24, 72 h. Only 24 h reperfusion resulted in a significant suppression in acetylcholine induced contractile response and in indomethacin induced relaxation. In the presence of adrenergic and cholinergic blockade a greater relaxant response to field stimulation (trains 10 s every min, 120 mA, 1 ms and 10 Hz) was unmasked in all groups except 24 h reperfused rats. Such effect was sensitive to N(G)-Nitro-L-arginine methyl ester (NOS unselective inhibitor) and the proteolytic enzyme alpha-chymotrypsin but resistant to aminoguanidine (iNOS selective inhibitor). In conclusion, in this rat model, intestinal mild ischemia/24 h reperfusion induces reversible changes in enteric motility attributable to a decrease in eicosanoids, nitric oxide and neuropeptides availability.

Alpha-melanocyte-stimulating hormone protects against mesenteric ischemia-reperfusion injury

Mesenteric ischemia-reperfusion (I/R) injury to the intestine is a common and often devastating clinical occurrence for which there are few therapeutic options. alpha-Melanocyte-stimulating hormone (alpha-MSH) is a tridecapeptide released by the pituitary gland and immunocompetent cells that exerts anti-inflammatory actions and abrogates postischemic injury to the kidneys and brainstem of rodents. To test the hypothesis that alpha-MSH would afford similar protection in the postischemic small intestine, we analyzed the effects of this peptide on intestinal transit, histology, myeloperoxidase activity, and nuclear factor-kappaB (NF-kappaB) activation after 45 min of superior mesenteric artery occlusion and <or=6 h of reperfusion. Rats subjected to I/R exhibited markedly depressed intestinal transit, histological evidence of severe injury to the ileum, increased myeloperoxidase activity in ileal cytoplasmic extracts, and biphasic activation of NF-kappaB in ileal nuclear extracts. In contrast, rats treated with alpha-MSH before I/R exhibited intestinal transit and histological injury scores comparable to those of sham-operated controls. In addition, the alpha-MSH-treated rats demonstrated less I/R-induced activation of intestinal NF-kappaB and myeloperoxidase activity after prolonged (6 h) reperfusion. We conclude that alpha-MSH significantly limits postischemic injury to the rat small intestine.

Ischemia/reperfusion-induced disruption of rat small intestine transit is reversed by total enteral nutrition

OBJECTIVES

A reduced blood flow to the gut is a consistent event after traumatic shock. Enteral nutrition support has been shown to reduce the septic morbidity after major trauma. We evaluated the effects of a transient ischemia followed by reperfusion (I/R) and an enteral nutrition support regimen on the motility of the small intestine of the rat.

METHODS

A catheter was placed in the upper duodenum and the small intestine was then made ischemic by clamping the superior mesenteric artery for 45 min; the arteries of sham rats were isolated but not clamped. Intestinal transit was evaluated by measuring the amount of fluorescein isothiocyanate-dextran (12 000 MW) in each of 10 intestinal sections at 30 min after injection through the duodenal catheter. The mean geometric center of marker distribution (MGC) was calculated for each group and compared. In a second study, I/R was followed by infusion of saline or a complete nutrient solution overnight, and transit was determined.

RESULTS

Intestinal transit (as the MGC) of I/R rats at 24 h after the beginning of reperfusion (3.5 +/- 0.2) and 48 h after the beginning of reperfusion (4.5 +/- 1.1) was significantly lower than that in the respective sham controls (5.1 +/- 0.3 and 5.9 +/- 0.5). The MGC for rats receiving a nutrient solution overnight during the reperfusion phase (6.0 +/- 1.1) was significantly increased compared with the MGC of 4.8 +/- 0.3 for rats receiving saline during the same period.

CONCLUSIONS

These results demonstrate a long-term deleterious effect of a non-lethal ischemia on intestinal transit and may be one explanation for many of the sequelae occurring after ischemia. In addition, these results demonstrate that a nutrient infusion will prevent the delayed transit. This may provide a partial explanation for the beneficial effects of total enteral nutrition in the clinical situation of posttraumatic injury.

Inducible nitric oxide synthase mediates gut ischemia/reperfusion-induced ileus only after severe insults

Inducible nitric oxide synthase (NOS 2) is thought to play a role in gut motility disorders that occur under proinflammatory conditions. Clinically, ileus occurs after sepsis and shock-induced gut ischemia/reperfusion (I/R). The purpose of this study was to determine if NOS 2 mediates impaired intestinal transit in well-established models of both moderate and severe gut ischemia/reperfusion. At laparotomy, Sprague-Dawley rats had duodenal catheters placed. Small intestinal transit was determined by quantitating the percentage tracer (FITC-dextran) in 10 equal segments of intestine 30 min after catheter injection [expressed as the mean geometric center (MGC) of distribution]. Transit was assessed at 6 and 24 h after gut ischemia [45 or 75 min of superior mesenteric artery occlusion (SMAO) with sham laparotomy as control]. In a separate set of experiments, N(6)-(iminoethyl)-L-lysine (L-NIL), a selective NOS 2 antagonist, was administered 1 h prior to laparotomy and transit was determined after 6 h as described above. Ileal NOS 2 expression was assessed by Western immunoblot and quantitative "real-time" RT-PCR. We observed that both 45 and 75 min of SMAO decreased intestinal transit at 6 h of reperfusion compared to sham. Ileal NOS 2 mRNA and protein were increased after 75, but not 45, min of SMAO. In addition, L-NIL improved transit after 75, but not 45, min of SMAO. We conclude that (1) NOS 2 is upregulated in the gut only after more severe ischemic insults, and (2) ileus is mediated, at least in part, by NOS 2 under these conditions.

Segmental intestinal ischemia: an improved method of producing small bowel injury

Previous animal models of intestinal ischemia-reperfusion have been successful in causing considerable mucosal damage, cellular destruction and sepsis. However, this often results in the death of the animal, making it impossible to examine the effects of modulators of the ischemic event. The sequence of morphologic and physiologic changes in the bowel from such injuries continues to be an area of intense examination. We have studied these changes by producing segmental intestinal ischemia in vivo in a rat model. By occluding a first-order branch of the superior mesenteric artery (SMA) and by selectively ligating terminal collateral branches, reproducible segmental intestinal ischemia was achieved. Bowel damage ranged from alterations in the villus structure to frank hemorrhagic necrosis of the intestinal wall. This model allows the study of hypoperfusion injury to the small intestine without total SMA occlusion, thus reducing the overall mortality.