Leukotriene D4 participates in colonic transit disturbances induced by intracolonic administration of trinitrobenzene sulfonic acid in rats

Severe Sepsis Secondary to Toxic Megacolon Revealing an Inflammatory Bowel Disease

Patients with inflammatory bowel disease can present with numerous infectious complications, including intra-abdominal abscess, perforations of the intestine, fistula formation, and the occurrence of septicemia. Toxic megacolon (TM) is a potentially fatal complication of inflammatory bowel disease (IBD) and is associated with high morbidity and mortality. In this case report, we report a 49-year-old male patient who was admitted to the intensive care unit for the management of severe sepsis that was secondary to an inaugural toxic megacolon complicating a silent inflammatory bowel disease, with a Lichtiger score of 11. Nonresponse to anti-bacterial therapy, noradrenaline, and intravenous corticosteroid therapy required an emergency total colectomy. After surgery, the patient died because of his unresolved septic shock. Correct management of this condition requires an accurate assessment of the patient's history, a correct physical examination, abdominal radiographs, and sigmoid coloscopy, and frequently requires surgery. The indications for surgery in cases of toxic megacolon, massive hemorrhage, perforation, peritonitis, or non-response to medical therapy are the most important ones. Patients with a history of inflammatory bowel disease are particularly prone to infectious complications since therapy for these inflammatory diseases is based on the use of immunosuppressive drugs and frequent abdominal surgeries.

Clostridioides difficile infection leading to fulminant colitis with toxic megacolon

Clostridioidesdifficile infection (CDI) is the culprit of millions of nosocomial infections in the United States. Programs that successfully decrease its incidence, therefore, render cost savings for the healthcare system. Toxic megacolon and perforation are two of the most significant complications with increased mortality rates. We report a 23-year-old nursing home resident hospitalized for fever, cough, and green sputum. After 3 days of antibiotic therapy, he developed abdominal distension, diarrhea, and vomiting and underwent a total colectomy. The colon was dilated to a maximum of 11 cm with markedly edematous mucosa and yellow pseudomembranes. Qualitative PCR of the stool detected Clostridioides difficile toxin B gene. While there is no consensus for the required interval between antibiotic treatment and CDI, this presentation 3 days after starting the antibiotic therapy is earlier than most proposed ranges.

Montelukast suppresses the development of irritable bowel syndrome phenotype possibly through modulating NF-κB signaling in an experimental model

Irritable bowel syndrome (IBS) is a functional gut disorder with multi-factorial pathophysiology that causes recurring pain or discomfort in the abdomen, as well as altered bowel habits. Montelukast, a well-known cysteinyl leukotriene receptor 1 (CysLT1R) antagonist, is widely used for the anti-inflammatory management of asthma. The present study aimed to evaluate the effects of pharmacological inhibition of CysLT1R on acetic acid-induced diarrhea-predominant IBS (D-IBS) in rats. Behavioral pain responses to noxious mechanical stimulation were decreased in the montelukast-treated rats as compared to the model animals following colorectal distension (CRD)-induced visceral hypersensitivity. Stool frequency decreased dose-dependently by montelukast in IBS rats exposed to restraint stress. A significantly shorter immobility time was also observed in IBS rats who received montelukast vs IBS group in the forced swimming test (depression-like behavior). Furthermore, there were significant decreases in the NF-κB protein expression, inflammatory cytokine (TNF-α, and IL-1ß) levels, and histopathological inflammatory injuries concomitant with increased anti-inflammatory cytokine, IL-10, in montelukast-treated rats compared with the IBS group. Cysteinyl leukotriene production and CysLT1R mRNA expression showed no remarkable differences among the experimental groups. The present results suggest the possible beneficial effects of montelukast in the management of D-IBS symptoms. The molecular mechanism underlying such effects, at least to some extent, might be through modulating CysLT1R-mediated NF-κB signaling. Yet, more studies are required to demonstrate the clinical potential of this drug for IBS therapy.

Toxic Megacolon: Background, Pathophysiology, Management Challenges and Solutions

Toxic megacolon (TM) is one of the fatal complications of inflammatory bowel disease (IBD) or any infectious etiology of the colon that is characterized by total or partial nonobstructive colonic dilatation and systemic toxicity. It is associated with high morbidity and mortality, and surgical management is necessary for the majority of the cases. An accurate history and physical examination, plain radiographs of the abdomen, sigmoidoscopy, and, most important of all, awareness of the condition facilitate diagnosis in most cases. Operative intervention is warranted when massive hemorrhage, perforation, or peritonitis complicate the clinical scenario or medical therapy fails to control the disease. We sought to review the management challenges of TM and its possible management strategies in this article.

Incidence, features, in-hospital outcomes and predictors of in-hospital mortality associated with toxic megacolon hospitalizations in the United States

Toxic megacolon (TM) is a potentially fatal condition characterized by non-obstructive colonic dilatation and systemic toxicity. It is most commonly caused by inflammatory bowel disease (IBD). Limited data for TM are available demonstrating incidence, in-hospital outcomes and predictors of mortality. We sought to investigate incidence, characteristics, mortality and predictors of mortality associated with it. Data were obtained from the Healthcare Cost and Utilization Project (HCUP)'s Nationwide Inpatient Sample (NIS) database from January 2010 through December 2014. An analysis was performed on SAS 9.4 (SAS Institute Inc., Cary, NC). Patients below 18 years were excluded. A mixed-effects logistic regression model was developed to analyze predictors of mortality. Thus, 8139 (weighted) cases of TM were diagnosed between 2010 and 2014. TM is more prevalent in women (56.4%) than in men (43.6%), with a mean age of onset at 62.4 years, affecting whites (79.7%) more than non-whites. The most common reason for hospital admission included IBD (51.6%) followed by septicemia (10.2%) and intestinal infections (4.1%). Mean length of stay was 9.5 days and overall in-hospital mortality was 7.9%. Other complications included surgical resection of the large intestine (11.5%) and bowel obstruction (10.9%). Higher age, neurological disorder, coagulopathy, chronic pulmonary disease, heart failure, and renal failure were associated with greater risk of in-hospital mortality. TM is a serious condition with high in-hospital mortality. Management of TM requires an inter-disciplinary team approach with close monitoring. Patients with positive predictors in our study require special attention to prevent excessive in-hospital mortality.

Clostridium difficile suppresses colonic vasoactive intestinal peptide associated with altered motility

We investigated whether Clostridium difficile toxin alters colonic tissue levels of vasoactive intestinal peptide (VIP) at the expense of changes in colonic motility in the isolated perfused rabbit left colon. Colonic inflammation was induced by the intracolonic administration of 10(-8) M C. difflcile toxin. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. C. difflcile administration produced histologic changes consistent with epithelial damage. This was associated with an increased production of prostaglandin E(2) and thromboxane B(2). Tissue levels of VIP but not substance P were significantly reduced. This was associated with an increased number of contractions per minute and an average force of each colonic contraction. These results suggest that tissue levels of VIP are suppressed by C. difflcile and may participate in colonic dysmotility during active inflammation.

Platelet-activating factor mediates trinitrobenzene induced dysmotility in the left colon

We investigated whether TNB alters colonic tissue levels of PAF at the expense of changes in colonic motility in the isolated perfused rabbit left colon. Colonic inflammation was induced by the intracolonic administration of 0.25 ml of 50% ethanol containing 30 mg of trinitrobenzene. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. TNB administration increased tissue levels of PAF and increased the average force of each colonic contraction. Pretreatment with the PAF receptor antagonist WEB-2170 prior to TNB infusion decreased tissue concentrations of PAF and ameliorated the altered motility parameters seen with TNB alone. These results suggest that PAF is stimulated by TNB and may participate in colonic dysmotility during inflammatory states.

TNBS-induced inflammation modulates the function of one class of low-threshold rectal mechanoreceptors in the guinea pig

The effects of trinitrobenzene sulfonic acid (TNBS)-induced inflammation on specialized, low-threshold, slowly adapting rectal mechanoreceptors were investigated in the guinea pig. Under isoflurane anesthesia, 300 microl saline or TNBS (15 mg/ml) in 30% ethanol was instilled 7 cm from the anal sphincter. Six or 30 days later, single unit extracellular recordings were made from rectal nerve trunks in flat-sheet in vitro preparations attached to a mechanical tissue stretcher. TNBS treatment caused macroscopic ulceration of the rectal mucosa at 6 days, which fully resolved by 30 days. Muscle contractility was unaffected by TNBS treatment. At 6 days posttreatment, responses of low-threshold rectal mechanoreceptors to circumferential stretch were increased, and the proportion of afferents responding with von Frey hair thresholds <or=0.1 mN and mechanoreceptor excitability in response to electrical stimulation were increased in TNBS-treated tissue, suggesting increased sensitivity of the mechanotransducer. Mechanoreceptor function at 30 days posttreatment was in most cases unchanged. The inflammatory mediator prostaglandin E(2) (1 microM) activated mechanoreceptors (6 days) in conjunction with contractile activity, but capsaicin (1 microM) failed to activate mechanoreceptors. Bradykinin (1 microM) activated mechanoreceptors independently of contractile activity and responses to stretch were increased in the presence of bradykinin. Both capsaicin and bradykinin activated unidentified stretch-insensitive afferents independently of contractile activity. Mechanoreceptor function is modulated at 6 days posttreatment but not at 30 days, suggesting a moderate increase in mechanoreceptor sensitivity in inflamed tissue but not after recovery. Other unclassified stretch-insensitive afferents are responsive to inflammatory mediators and capsaicin and may be involved in aspects of visceral sensation.

Natural history of infant reflux esophagitis: symptoms and morphometric histology during one year without pharmacotherapy

OBJECTIVES

To determine the natural history of infant gastroesophageal reflux disease (GERD) with esophagitis, we periodically analyzed symptoms and biopsies during 1 yr in 19 infants randomly assigned to placebo in a pharmacotherapy study.

METHODS

One hundred infants who were referred during 1994-1999 for GERD, were unresponsive to 2-wk life-style measures, and manifested morphometric reflux esophagitis, were assigned at random to one of four treatment arms. This analysis examines the 19 (ages 2.8-6.0 months) assigned to placebo who returned for initial follow-up. SYMPTOMS and esophageal biopsy were assessed at baseline and 2, 4, 6, and 12 months. At any visit with both symptoms and biopsy unimproved, infants were "rescued" to open label active drug.

RESULTS

By 12 months, 10/19 completed without rescue; the 9 others withdrew (3) or required pharmacotherapy (6).

SYMPTOMS

Among the 10 nonrescued completers, parents' global score rated 9 "completely well," and 1 "improved." Comparing 12-month symptoms to baseline symptoms in the 10 completers, fewer reported regurgitation >3/day, >1 Tbsp, or that was uncomfortable; crying >1 h/d, or during or after feeds; or arching spells or abnormal hiccups (p < 0.05, chi(2)). Biopsy: None of the 10 ever had normal biopsies (basal cell layer <25% and papillary height <53% of epithelial thickness). One had normal papillary height, but abnormal basal thickness. Five others had normal basal thickness, but all five of them had abnormal papillary height.

CONCLUSION

Although symptoms improved in more than half of the infants with reflux esophagitis followed longitudinally for 1 yr without pharmacotherapy, histology remained abnormal.

A new look at toxic megacolon: an update and review of incidence, etiology, pathogenesis, and management

Toxic megacolon (TM) is an infrequent but devastating complication of colitis. Numerous forms of colonic inflammation can give rise to TM but the majority occur in individuals with inflammatory bowel disease (IBD). Recently there has been a marked increase in the number of reports of TM associated with pseudomembranous colitis. Because of the associated high morbidity and mortality, early recognition and management of TM is of paramount importance. The mechanisms involved in development of TM are not clearly delineated, but chemical mediators such as nitric oxide and interleukins may play a pivotal role in the pathogenesis. New evidence suggests that TM and its associated morbidity may be predicted by the extent of small bowel and gastric distension in patients with colitis. CT scanning may also play an important role the management of TM, in that it may be the only noninvasive mode to detect subclinical perforations and abscesses. Management involves close medical attention, supportive care, and treatment of the underlying colitis. Possible exacerbating factors such as narcotic and anticholinergic medications must be withdrawn, and colonic decompression via tube drainage or positional techniques must be considered. Signs of progression or complications of the disease must be treated aggressively with surgical intervention, as delay is associated with even greater risk of mortality.

Acute effects of the cys-leukotriene-1 receptor antagonist, montelukast, on experimental colitis in rats

Cysteinyl leukotrienes play a part in inflammatory reactions such as inflammatory bowel diseases. The aim of the present study was to evaluate the acute effects of a cys-leukotriene-1 receptor antagonist, montelukast, on trinitrobenzene sulphonic acid (TNBS)-induced colitis in rats. Montelukast (5, 10 or 20 mg kg(-1) day(-1)), a 5-lipoxygenase inhibitor, zileuton (50 or 100 mg kg(-1) day(-1), a positive control), or the vehicle was administered intracolonically to the rats twice daily throughout the study, starting 12 h before the induction of colitis with TNBS. The severity of colitis (macroscopic and histological assessment, as well as myeloperoxidase activity), the protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2, and eicosanoid production in colonic tissue incubation were assessed 24 and 72 h after colitis induction. Montelukast increased prostaglandin E(2) production at 24 h and tended to reduce the cyclooxygenase-2 protein expression at 72 h, but did not influence the severity of colitis. Zileuton failed to decrease the inflammatory reaction in spite of reduced leukotriene B(4) production at 72 h. The results suggest that drugs that block cysteinyl leukotriene receptors have limited potential to ameliorate acute TNBS-induced colitis, but that they exert some beneficial effects which make them capable of modulating the course of colitis.

Effect of TNBS-induced morphological changes on pharmacological contractility of the rat ileum

Intraluminal instillation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in ethanol is a classical model of colitis in the rat. Little is known about the time-related effect of TNBS on the contractility and morphology of the rat ileum. After 36 h, TNBS induced acute ileitis. Spontaneous activity of longitudinal muscle strips was decreased, as were receptor- and nonreceptor-mediated contractions and contractions induced by electrical stimulation. After 1 week, mucosal integrity was restored, although the thickness of both mucosal and muscle layers was increased. Spontaneous activity, receptor- and nonreceptor-mediated contractions and electrically induced contractions of longitudinal muscle strips were increased due to hypertrophy and hyperplasia of smooth muscle cells. This was confirmed in the contractility study of individual muscle cells. Functional alterations after 1 week were restricted to a decreased response to substance P. TNBS-ileitis in the rat lacks a chronic phase and is accompanied by functional hypocontractility of longitudinal smooth muscle cells during the acute inflammation, whereas the contractility of the longitudinal muscle layer is increased in the postinflammation phase due to structural alterations. There is a selective inhibition of the response to substance P in the postinflammation phase.

The spectrum of pediatric eosinophilic esophagitis beyond infancy: a clinical series of 30 children

OBJECTIVES

Eosinophilic esophagitis, previously confused with esophageal inflammation due to gastroesophageal reflux, has recently begun to be distinguished from it. We undertook this analysis of our large series of children with the condition to clarify its spectrum: its presenting symptoms; its relation to allergy, respiratory disease, and reflux; its endoscopic and histological findings; and its diagnosis and therapy.

METHODS

We analyzed the details of our clinical series of 30 children with eosinophilic esophagitis, defining it as > or =5 eosinophils per high power field in the distal esophageal epithelium. Retrospective chart review was supplemented by prospective, blinded, duplicate quantitative evaluation of histology specimens, and by telephone contact with some families to clarify subsequent course. Presentation and analysis of the series as a whole is preceded by a case illustrating a typical presentation with dysphagia and recurrent esophageal food impactions.

RESULTS

Presenting symptoms encompass vomiting, pain, and dysphagia (some with impactions or strictures). Allergy, particularly food allergy, is an associated finding in most patients, and many have concomitant asthma or other chronic respiratory disease. A subtle granularity with furrows or rings is newly identified as the endoscopic herald of histological eosinophilic esophagitis. Histological characteristics include peripapillary or juxtaluminal eosinophil clustering in certain cases. Association with eosinophilic gastroenteritis occurs, but is not common. Differentiation from gastroesophageal reflux disease is approached by analyzing eosinophil density and response to therapeutic trials. Therapy encompasses dietary elimination and anti-inflammatory pharmacotherapy.

CONCLUSION

Awareness of the spectrum of eosinophilic esophagitis should promote optimal diagnosis and treatment of this elusive entity, both in children and in adults.

Progressive alterations in circular smooth muscle contractility in TNBS-induced colitis in rats

The present study was designed to investigate inflammation-induced changes in smooth muscle responses to acetylcholine and the tachykinins that may contribute to the abnormal motility associated with inflammatory bowel disease. Colitis was induced in male Sprague-Dawley rats by intrarectal administration of trinitrobenzenesulphonic acid in ethanol. After either 4 h (acute) or 7 days (chronic) the distal colon was taken for in vitro measurement of smooth muscle tension and histological assessment. Acute colitis featured injury and neutrophilic infiltration confined to the mucosa while chronic inflammation showed marked injury, lymphocytic infiltration and muscle thickening. Acute inflammation increased responses to substance P and acetylcholine but decreased responses to neurokinin A. The enhanced response to substance P was dependent on nerves, while the decreased response to neurokinin A reflected a reduction in activity at the level of the smooth muscle. In the saline group, there was evidence of cholinergic interaction with substance P, but not neurokinin A. Substance P modulation of cholinergic nerves was absent in acute inflammation. Responses to all neurotransmitters were decreased in the chronic stage. These data demonstrate progressive changes in the smooth muscle function during acute and chronic colitis that may contribute to the abnormal motility associated with inflammatory bowel disease.

Lack of effectiveness of the platelet-activating factor antagonist SR27417A in patients with active ulcerative colitis: a randomized controlled trial. The Platelet Activating Factor Antagonist Study Group in Ulcerative Colitis

BACKGROUND & AIMS

Platelet-activating factor (PAF) is increased during relapse of ulcerative colitis. In animal models of experimental colitis, specific inhibition of PAF has reduced inflammation. The aim of this study was to evaluate the efficacy and safety of the PAF antagonist SR27417A in moderately active UC.

METHODS

A double-blind multicenter trial was conducted during a 28-day period in hospital outpatients with an exacerbation of ulcerative colitis. Patients were randomized to receive 10 mg/day SR27417A or placebo, and both groups were also given 2.4 g mesalazine. Patient classification at the end of the treatment period was based on sigmoidoscopy and clinical scores.

RESULTS

One hundred fifty-one subjects entered the study (75 placebo and 76 SR27417A). The remission rate between placebo- and SR27417A-treated patients at 28 days was not significantly different (29.0% and 35.6% respectively; P = 0.44). Similarly, 49.2% treated with SR27417A had a definite or possible improvement of their symptom score compared with 48.3% of those treated with placebo (P = 0.43). Four subjects in the placebo group and 5 subjects in the SR27417A group discontinued the drug treatment because of adverse events. No significant adverse events were thought to be caused by SR27417A.

CONCLUSIONS

Although the specific PAF antagonist SR27417A is safe in humans, there is no evidence of efficacy in the treatment of acute ulcerative colitis.

Distribution of calcitonin gene-related peptide, somatostatin, substance P and vasoactive intestinal polypeptide in experimental colitis in rats

Immunohistochemistry was used to examine the distribution of calcitonin gene-related peptide (CGRP), substance P, somatostatin and vasoactive intestinal polypeptide (VIP) in experimental colitis induced with trinitrobenzene sulphonic acid (TNBS) in rats. CGRP immunoreactivity was observed throughout the colonic wall. A significant reduction of CGRP-immunoreactive (IR) nerve fibres was observed in the mucosa after the induction of colitis. After TNBS treatment substance P immunoreactivity was reduced throughout the colon; however, after 7 days there was a marked re-innervation of the circular muscle. Somatostatin immunoreactivity was distributed sparsely within the colonic wall, and was comparatively less affected by colitis. VIP immunoreactivity was abundantly distributed in the colonic wall and underwent an immediate reduction in the mucosa after TNBS treatment. After 2 days, there was a consistent and progressive increase in the number and density of VIP-IR nerve fibres in the inflamed colon, particularly the circular muscle. This change was associated with a proliferation of nerve fibres within the muscle layers. It was concluded that the early decrease in these neuropeptides was consistent with release from peripheral nerve terminals or the loss of nerves during the initial stages of colonic inflammation, which may be an essential condition for the development of colitis in this model. The observation that the intensity and density of substance P and VIP-IR nerve fibres increased in the circular muscle 7 days after the induction of colitis suggests their possible involvement in tissue repair.

Induction of nitric oxide synthase in colonic smooth muscle from patients with toxic megacolon

BACKGROUND & AIMS

Colonic inflammation may lead to motility disturbances, including severe atony. Nitric oxide is released by inflamed tissue and induces smooth muscle relaxation. The aim of this study was to analyze NO generation pathways in colonic tissue from patients who had ulcerative colitis with or without toxic megacolon and in tumor-free samples from patients with colonic neoplasm.

METHODS

Enzymatic activity was determined by transformation of [14C]arginine to [14C]citrulline in mucosa and muscular layer samples. Immunostaining of tissue sections with antibody against inducible NO synthase was investigated. The effects of endotoxin on NO synthase activity was tested in muscle strips from human colon.

RESULTS

Ca(2+)-independent NO synthase was undetectable or very low in muscularis propria from tumor and colitis controls. In contrast, specimens from patients with toxic megacolon had high activity (P < 0.05). Positive immunostaining for inducible NO synthase was found in muscular layers from patients with megacolon but not in tumor and colitis controls. Finally, endotoxin induced Ca(2+)-independent NO synthase activity in colonic muscle.

CONCLUSIONS

Toxic megacolon is associated with the appearance of inducible NO synthase in the colonic muscularis propria. Local generation of excessive amounts of NO may be responsible for the colonic dilatation that is the hallmark of this syndrome.

Evidence for mast cell, leukotriene and nitric oxide involvement in the regulation of the adrenoceptor number of inflamed small intestine in guinea pigs

Changes in the populations of neurotransmitter receptors involved in the control of intestinal smooth muscle function have been associated with the altered motility of the inflamed gut. Thus, trinitrobenzenesulphonic acid (TNBS)-induced gut inflammation is accompanied by an increase in alpha- and a decrease in beta-adrenoceptor numbers in guinea pig small intestine. In the present study, we investigated the effects of anti-inflammatory compounds (cyclooxygenase inhibitor indomethacin, lipooxygenase inhibitor MK-886, nitric oxide synthase inhibitor NG-nitro-L-arginine methylester (L-NAME), mast cell stabilizer doxantrazole) on TNBS-induced adrenoceptor changes. Smooth muscle adrenoceptor populations, labelled by subtype-specific radioligands 6 days after TNBS, were significantly different from those of sham-treated controls: alpha 1- and alpha 2-adrenoceptor numbers increased by more than 50%, while beta-adrenoceptor numbers decreased by more than 50%. These changes, associated with severe inflammation as assessed histologically and by myeloperoxidase assay, were prevented by doxantrazole or L-NAME, and only partly by MK-886. In contrast, indomethacin did not prevent these changes. It appears then that: (a) mast cell mediators, nitric oxide and leukotrienes are likely to contribute to TNBS-induced changes in adrenoceptor populations in the guinea pig inflamed intestine; (b) there is no evidence for prostanoid involvement in this process. It was suggested that changes in smooth muscle adrenoceptor populations may be an important mechanism by which gut inflammation alters intestinal motility.

Effect of leukotriene C4D4 antagonist on colonic damage induced by intracolonic administration of trinitrobenzene sulfonic acid in rats

We examined the effects of eicosanoid antagonists on colonic damage induced by trinitrobenzene sulfonic acid (TNB) in a rat inflammatory bowel model. TNB (30 mg) dissolved in 0.25 ml of 50% ethanol, was given intrarectally. The appropriate doses of ONO-1078 (a leukotriene C4D4 antagonist), ONO-4057 (a leukotriene B4 antagonist), and OKY-046 (a thromboxane A2 synthetase inhibitor) were given to obtain the same blood level, either 4 h before (pre-treatment model) or 24 h after (the post-treatment model) the administration of TNB (n = 8 in all groups). Drugs were given once daily for 6 days through a gastric feeding tube. Autopsy was performed on the 7th day. Colonic damage was assessed in terms of colonic damage scores, and myeloperoxidase (MPO) activity and eicosanoid concentrations in colonic tissues were measured. Compared with the group given TNB alone, the colonic damage score was reduced to 10% in the pre-treatment model with ONO-1078, but the score was not reduced in other groups, MPO activity was not changed in any group. The concentration of leukotriene C4 was reduced with ONO-1078 treatment, in both pre- and post-treatment models. These results demonstrated that a leukotriene C4D4 antagonist reduced colonic inflammation; however, its anti-inflammatory effect was limited in this colitis model.

Platelet-activating factor mediates trinitrobenzene induced colitis

Platelet-activating factor (PAF) is an endogenous phospholipid which may be an important mediator of shock and inflammation. Recent evidence suggests that PAF plays a role in the development of ischemic colitis and inflammatory bowel disease. Its effects are mediated by second messengers, including the arachidonic acid metabolites. Using an ex vivo isolated left colon rabbit perfusion model, our aims were to determine whether exogenously administered trinitrobenzene sulfonic acid (TNB), which produces experimental colitis, stimulates both PAF and eicosanoid release in the colon, and if so, whether this effect can be blocked by a PAF antagonist. Colonic inflammation was induced by the intracolonic administration of 0.25 ml of 50% ethanol containing 30 mg of TNB. Tissue and perfusate concentrations of the eicosanoids, [prostaglandin E (PGE2), 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TXB2), leukotriene B4 (LTB4)] and the autocoid PAF were measured by ELISA. During TNB infusion there was a significant increase in tissue levels of PAF compared to control colons. Additional studies performed pretreating the colons with the PAF receptor antagonist WEB-2170 prior to TNB infusion blocked PAF release. TNB stimulated release of luminal eicosanoids except LTB4 and suppressed release of tissue prostanoids. Pretreatment with WEB-2170 prior to TNB inhibited luminal eicosanoids, and inhibited PGE2 and prostacyclin, but not TX tissue suppression. Inhibition of TNB-stimulated PAF release by WEB-2170 suggests that PAF may play a role in TNB-induced colitis and this phenomenon may mediate tissue injury.

Role of intestinal microflora in chronic inflammation and ulceration of the rat colon

Bacteria and their products stimulate inflammatory responses. The effects of different antimicrobial regimens (amoxicillin/clavulanic acid, tobramycin, imipenem, vancomycin, metronidazole) were investigated on the course of experimental colitis induced by trinitrobenzenesulphonic acid (TNB) in the rat. On day 7 and 21 after the induction of colitis, matched groups of control and antibiotic treated rats were subjected to colonic dialysis to measure eicosanoid release, and killed for morphological assessment of the colonic lesions (macro and microscopic scores). Stool samples were cultured. Selective antibiotic treatment against Gram positive, Gram negative or anaerobic bacteria had no effect on colonic lesion scores. By contrast, certain broad spectrum antibiotics (amoxicillin/clavulanic acid or the association of imipenem plus vancomycin) significantly reduced macro and microscopic scores. Rats receiving these antibiotics did not develop chronic colitis as shown by the virtual absence of colonic strictures, adhesions, fibrosis, and granulomas. On day 21 after TNB, the intracolonic release of prostaglandin E2, thromboxane B2, and leukotriene B4 was significantly higher in control than in antibiotic treated rats. Control stool cultures showed abundant colony forming units of both aerobic and anaerobic bacteria. Amoxicillin/clavulanic acid and imipenem plus vancomycin induced appreciable reductions in luminal bacteria. In conclusion, certain broad spectrum antibiotics prevent chronic colitis. The normal colonic flora seems to play an important pathogenetic part in the progression of inflammatory colonic lesions to chronicity.

Experimental colitis alters visceromotor response to colorectal distension in awake rats

The influence of intermittent colorectal distension (CRD) on proximal colonic motility and abdominal pain perception was investigated in awake rats equipped with intraparietal electrodes on the cecum, proximal colon, and abdomen, before and three days after rectocolitis induction by trinitrobenzene sulfonic acid (TNB)/ethanol. The normal myoelectrical activities of cecum and proximal colon [5.2 +/- 0.5 and 9.7 +/- 0.7 long spike bursts (LSB) per 5 min, respectively] were significantly (P < 0.05) and gradually decreased by control CRD, at diameters above 9 mm. At the maximum CRD diameter (13.7 mm), 1.6 +/- 0.6 cecal and 3.9 +/- 0.8 colonic spike bursts occurred per 5 min (respectively, 69 and 60% decreases). This upstream inhibition was accompanied by a significant (P < 0.05) and gradual increase in abdominal contractions (0.4 +/- 0.4 per 5 min in control vs 23.4 +/- 1.9 in response to 13.7 mm in diameter). Three days after TNB/ethanol, visceromotor and abdominal responses were significantly (P < 0.05) enhanced at the least CRD diameter of 9 mm (cecum: 3.1 +/- 0.4 after TNB vs 5.0 +/- 0.7 in control; proximal colon: 5.1 +/- 0.9 vs 9.3 +/- 2.2; abdomen: 7.7 +/- 1.5 vs 0.5 +/- 0.4). We conclude that in awake rats, CRD evokes both abdominal contractions in response to pain and inhibition of cecal and proximal colonic motility, which thresholds are both lowered by TNB-induced rectocolitis.

Effect of platelet-activating factor and its antagonists on colonic dysmotility and tissue levels of colonic neuropeptides

We investigated whether platelet-activating factor (PAF) alters colonic tissue levels of substance P and vasoactive intestinal peptide (VIP), two neuropeptides that regulate colonic motility. Left colons were harvested from NZ White Rabbits and underwent vascular perfusion via the inferior mesenteric artery. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. Colons were perfused with either buffered saline alone or with 5.0 x 10(-5) M PAF. PAF administration increased tissue VIP and substance P levels and decreased the force of colonic contractions. Pretreatment with WEB-2170 or alprazolam decreased concentrations of both tissue neuropeptides, and decreased the force of colonic contractions and minute motility index. These results suggest that both VIP and substance P are stimulated by PAF and may participate in colonic dysmotility during inflammatory states.

Inverse regulation of alpha- and beta-adrenoceptors during trinitrobenzenesulfonic acid (TNB)-induced inflammation in guinea-pig small intestine

The hypothesis has been raised that intestinal motor disturbances induced by inflammation of the digestive tract may reflect alterations in intestinal cell-membrane receptors. This question has been addressed herein for adrenoceptors by performing [3H]prazosin, [3H]rauwolscine and [3H]DHA binding studies on guinea-pig jejunal smooth-muscle membrane preparations from both healthy controls and 3, 6, and 10 days after TNB-induced intestinal inflammation. Each of the adrenoceptor subtype-selective radioligands used bound selectively to a single saturable class of sites, with no significant (p < 0.05) variation of dissociation constant (KD) values along the inflammatory process. In contrast maximal binding capacities (Bmax) for the different radioligands varied moderately but significantly (p < 0.05 and p < 0.01) according to the time after TNB injection. The alpha-adrenoceptors were significantly upregulated, respectively from (mean +/- SE in fmoles/mg of proteins) 27 +/- 3.8 (controls) to 91 +/- 3.1 (day 10) for the alpha 1-subtype, and from 26 +/- 2.7 (controls) to 102 +/- 5.9 (day 10) for the alpha 2-subtype. In contrast beta-adrenoceptors were down-regulated from 384 +/- 34.6 (controls) to 158 +/- 17.2 (day 10). These findings highlighted an apparently inverse pathological regulation of intestinal alpha- and beta- adrenoceptor densities. They suggest that changes in intestinal adrenoceptors, probably resulting from functional denervation of the inflamed bowel tissue, may contribute to the altered intestinal motility observed in inflammatory bowel diseases.

Platelet-activating factor and interleukin 1 are involved in colonic dysmotility in experimental colitis in rats

BACKGROUND

Intracolonic administration of trinitrobenzene sulfonic acid (TNBS) to rats produces chronic colitis associated with an increased release of eicosanoids, platelet-activating factor (PAF), and interleukins.

METHODS

Motor effects of TNBS on proximal colon were evaluated electromyographically in rats. Mediator involvement was investigated using eicosanoids and PAF antagonists.

RESULTS

The colonic myoelectrical activity was 59 +/- 17 spike bursts per hour lasting 6.9 +/- 1.3 seconds. Two to eight days after TNBS treatment, spike-burst duration was significantly (P < 0.05) higher, with a maximal 1.5-4-fold enhancement at day 3. These alterations were significantly (P < 0.05) reduced by daily treatment with MK-886, a 5-lipoxygenase inhibitor (10 mg/kg, orally), whereas indomethacin (1 mg/kg per day, intramuscularly) was ineffective. At day 3, RP55778, a PAF antagonist (45, 60 mg/kg, intraperitoneally), and rIRAP, an interleukin 1 antagonist (0.3 mg/kg, intraperitoneally) but not KT1-32, a thromboxane A2 antagonist (30, 60 mg/kg orally), nor SKF104,353, a leukotriene D4 antagonist (2, 4 mg/kg, orally), significantly (P < 0.05) reduced the TNB-induced motor effects.

CONCLUSION

TNBS-induced colitis in rats involves a delayed long-lasting dysmotility involving PAF, interleukin 1, and some leukotrienes but not leukotriene D4, thromboxane A2, or other cyclo-oxygenase products.