Altered calcium-handling properties of jejunal smooth muscle from the nematode-infected rat

Modulation of the immune response by helminths: a role for serotonin?

The mammalian gut is a remarkable organ: with a nervous system that rivals the spinal cord, it is the body’s largest repository of immune and endocrine cells and houses an immense and complex microbiota. Infection with helminth parasites elicits a conserved program of effector and regulatory immune responses to eradicate the worm, limit tissue damage, and return the gut to homeostasis. Discrete changes in the nervous system, and to a lesser extent the enteroendocrine system, occur following helminth infection but the importance of these adaptations in expelling the worm is poorly understood. Approximately 90% of the body’s serotonin (5-hydroxytryptamine (5-HT)) is made in enterochromaffin (EC) cells in the gut, indicative of the importance of this amine in intestinal function. Signaling via a plethora of receptor subtypes, substantial evidence illustrates that 5-HT affects immunity. A small number of studies document changes in 5-HT levels following infection with helminth parasites, but these have not been complemented by an understanding of the role of 5-HT in the host–parasite interaction. In reviewing this area, the gap in knowledge of how changes in the enteric serotonergic system affects the outcome of infection with intestinal helminths is apparent. We present this as a call-to-action by investigators in the field. We contend that neuronal EC cell–immune interactions in the gut are essential in maintaining homeostasis and, when perturbed, contribute to pathophysiology. The full affect of infection with helminth parasites needs to define, and then mechanistically dissect the role of the enteric nervous and enteroendocrine systems of the gut.

Curcumin reverses attenuated carbachol-induced contraction of the colon in a rat model of colitis

BACKGROUND

Curcumin ameliorates colitis whether it reverses colitis-induced reduction in colonic contractility remains to be investigated.

OBJECTIVES

To investigate the effect of curcumin on colitis-induced reduction of carbachol-induced contraction in colon segments from rats treated with trinitrobenzenesulphonic acid.

METHODS

Colitis was induced in rats by intra rectal administration of trinitrobenzenesulphonic acid and followed for 5 days. A group of animals which received trinitobenzene sulphonic acids was treated with curcumin (100 mg/Kg and 200 mg/kg body weight) 2 hrs prior to induction of colitis. The controls received phosphate buffered saline in a similar fashion. Markers of inflammation and contractility of colon were assayed using standard procedures.

RESULTS

Induction of colitis was associated with increased myeloperoxidase activity and malondialdehyde levels, gross histological changes characterized by infiltration of inflammatory cells. All these changes were prevented by treatment with curcumin (100 mg/kg). Treatment with curcumin also reduced the histological scores from 3.34+/-0.40 to 1.75+/-0.30 confirming an anti-inflammatory effect of curcumin in this experimental model of colitis. Colonic reactivity to carbachol was decreased in colitis affecting the maximum response but not sensitivity. Treatment with curcumin had no effect on sensitivity of the colon to carbachol in any of the preparations. Curcumin however reversed the decrease in carbachol-induced contraction associated with trinitrobenzenesulphonic acid treatment. The same dose of curcumin had no effect on either the potency of or the maximum response to carbachol in control rats. Tissue expression of NF-kB was increased in colon segments from trinitrobenzenesulphonic acid -treated rats and this was inhibited in rats treated with curcumin.

CONCLUSIONS

Based on these findings it is concluded that curcumin prevented the reduction in carbachol-induced contraction in trinitrobenzenesulphonic acid -treated rats by modulating NF-kB signaling pathway.

Involvement of CPI-17 downregulation in the dysmotility of the colon from dextran sodium sulphate-induced experimental colitis in a mouse model

The mechanism of gastrointestinal dysmotility in inflammatory bowel disease has not been clarified. In this study, we examined the mechanism involved in the inflamed distal colon isolated from a mouse model of dextran sodium sulphate-induced ulcerative colitis (DSS-treated mouse). Although substance P-induced contraction was not changed, carbachol-induced contraction was reduced in the DSS-treated mouse colon. Pre-incubation with the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) or the cyclooxygenase inhibitor indomethacin did not reverse the carbachol-induced contraction in the DSS-treated mouse colon. In semi-quantitative reverse transcription-polymerase chain reaction experiments and Western blot analysis, muscarinic M3 receptor expressions were not changed. The Ca2+ -sensitization of contractile elements induced by carbachol with GTP or GTPgammaS was reduced in the beta-escin-permeabilized DSS-treated mouse colon. Although the expression of proteins such as rhoA, ROCK1, ROCK2 or MYPT1 in smooth muscles was not changed, the expression of CPI-17, the functional protein involved in smooth muscle Ca2+ -sensitization, was significantly decreased in the DSS-treated mouse colon. These results suggest that the suppression of carbachol-induced contraction in mice with colitis is attributable at least partially to the increased activity of myosin phosphatase following the downregulation of CPI-17.

Infection with the cestode Hymenolepis diminuta induces changes in acetylcholine metabolism and muscarinic receptor mRNA expression in the rat jejunum

Total and neuron-specific uptake of [3H] choline into smooth muscle/myenteric plexus (SM/MP) preparations from the jejunum of rats infected with five Hymenolepis diminuta for 30 days compared to uninfected rats was significantly increased, as was choline acetyltransferase activity and acetylcholine biosynthesis. Although acetylcholinesterase and total cholinesterase activity levels in SM/MP preparations from infected rats were not significantly different from uninfected animals, pseudocholinesterase activity was significantly elevated in infected rats. Infection resulted in a significant elevation in the relative expression of muscarinic 2 (M2) receptor mRNA in jejunum compared to uninfected rats. Conversely, in rats infected with 50 worms for 30 days, the relative expression of muscarinic 1 (M1) receptor mRNA in the jejunum was significantly depressed, while the expression of M2 receptor mRNA was not significantly different from that in five worm infections. The relative expression of muscarinic 3 receptor mRNA was unaffected by infection. The present study shows that infection of rats with low numbers of an enteric cestode leads to a significant modulation of the cholinergic components of the myenteric plexus and M2 receptor mRNA, and that large number of worms result in suppression in the relative expression of M1 receptor mRNA.

Mechanisms underlying the maintenance of muscle hypercontractility in a model of postinfective gut dysfunction

BACKGROUND & AIMS

Acute gastroenteritis is a strong risk factor for the development of irritable bowel syndrome (IBS). We have developed an animal model in which transient acute infection leads to persistent muscle hypercontractility. Here, we investigate the mechanisms underlying the maintenance of this hypercontractility in the postinfective (PI) state.

METHODS

Muscle contraction and messenger RNA (mRNA) or protein expression of cytokines were examined from jejunal longitudinal muscle cells of NIH Swiss mice infected with Trichinella spiralis or incubated with or without cytokines.

RESULTS

During acute infection, interleukin (IL)-4 or IL-13, transforming growth factor (TGF)-beta1, and cyclooxygenase (COX)-2 were increased in the muscle layer ( P < .05). In the PI phase of the model, T helper (Th)2 cytokines returned to normal, but TGF-beta1 remained in the muscle ( P < .05). Exposure of muscle cells to IL-4 or IL-13 increased TGF-beta1 ( P < .01), COX-2 protein, and prostaglandin (PG)E 2 . Exposure of muscle cells to TGF-beta1 increased PGE 2 ( P < .05) and COX-2 protein. Incubation of tissue with IL-4, IL-13, TGF-beta1, or PGE 2 enhanced carbachol-induced muscle cell contractility ( P < .05). COX-2 inhibitor attenuated TGF-beta1-induced muscle hypercontractility ( P < .05).

CONCLUSIONS

These results support the hypothesis that Th2 cytokines induce muscle hypercontractility during infection by a direct action on smooth muscle. The maintenance of hypercontractility results from Th2 cytokine-induced expression of TGF-beta1 and the subsequent up-regulation of COX-2 and PGE 2 at the level of the smooth muscle cell. We propose that PI gut dysfunction reflects mediator production in the neuromuscular tissues and that this may occur in PI-IBS.

Functional effects of dextran sulphate sodium (DSS) treatment on the longitudinal muscle of rat distal colon

1. The current study addressed how acute colitis, induced in male Sprague-Dawley rats by the administration of dextran sulphate sodium (DSS) in their drinking water, may affect some functional properties of the longitudinal muscle layer of the distal colon. 2. Dextran sulphate sodium was provided at a concentration of 3% for 3 or 7 days, or 5% for 7 days, and the rats were thereafter killed. Specimens of the distal colon were taken for histology or for organ bath experiments. 3. The colitis score increased significantly with increasing dose of DSS administered. At 5% concentration, there was sometimes even transmural inflammation. Functionally, there was a progressive increase in optimal preload (P(o)) for the contractile response to carbachol (1 microM), in relation to the severity of the colitis. At 5% DSS, the magnitude of the response to carbachol at P(o) was significantly increased compared with control rats. Such an effect could not be verified when, instead, K+ (60 mM) was used as a spasmogen. 4. It is concluded, that the colitis score increased in severity progressively with increasing amounts of DSS administered. The longitudinal muscle layer was functionally affected by the inflammation. Thus, there was a progressive increase in optimal preload for muscle contraction. Moreover, severe colitis resulted in an increase of the contractile response to carbachol, while a significant increase in the response to depolarization with K+ could not be found.

Motilin receptor density in inflamed and noninflamed tissue in rabbit TNBS-induced colitis

Trinitrobenzenesulphonic acid (TNBS)-induced colitis decreases the contractile response of the rabbit colon to motilin, and inflammation may increase plasma motilin levels. We studied whether the decreased contractility could be due to a down-regulation of motilin receptors, caused by increased plasma motilin levels. As this would affect all tissues, uninflamed sites were studied as well. Colitis was induced by different doses (100-150 mg kg-1) of TNBS. In the colon, the TNBS dose-dependent decrease of the contractile response towards motilin was reflected in a decrease in motilin receptor density. In contrast, in the antrum, receptors were upregulated by 150 mg kg-1 TNBS, while central motilin receptors in the cerebellum were not affected. Plasma motilin levels were not influenced by inflammation, although the motilin content and mRNA expression in the duodenal and jejunal mucosa, but not in the colon, was significantly increased. The opposite was true for interleukin-1beta and interleukin receptor antagonist mRNA expression. We conclude that the decreased motilin contractility in rabbit colitis is due to a downregulation of motilin receptors in the colon, but this is not caused by chronic hormonal stimulation.

Alterations of intestinal motor responses to various stimuli after Nippostrongylus brasiliensis infection in rats: role of mast cells

Nippostrongylus brasiliensis infection induces jejunal mastocytosis associated with enteric nerve remodelling in rats. The aim of this study was to evaluate the intestinal motility responses to meals and to neurotransmitters involved in the control of gut motility (acetylcholine (carbachol), substance P and neurokinin A) in both control and N. brasiliensis-infected rats 30 days post-infection. All rats were equipped with NiCr electrodes in the jejunum to record myoelectrical activity. The duration of disruption of the jejunal migrating myoelectrical complexes (MMC) induced by the different stimuli was determined. Meal ingestion and substance P administration disrupted the MMC pattern for similar durations in the two groups. Carbachol and neurokinin A induced a significantly longer MMC disruption in post-infected rats than in controls (125 +/- 8.3 vs. 70 +/- 6 min for carbachol 100 microg kg-1 and 51 +/- 4 vs. 40 +/- 2 for neurokinin A 50 microg kg-1). The enhanced motor response in postinfected rats was reduced by previous mast cell stabilization with ketotifen or mast cell degranulation with compound BrX 537 A. In conclusion, the increased intestinal motor reactivity to carbachol and neurokinin A in post-N. brasiliensis-infected rats depends upon intestinal mast cell hyperplasia and degranulation.

Differential inflammatory modulation of canine ileal longitudinal and circular muscle cells

The aim of this study was to identify the subtypes of muscarinic receptors that mediate in vivo and in vitro canine ileal longitudinal muscle contractions and whether their role is modulated by inflammation. Previous studies have reported that circular muscle contractions are suppressed in ileal inflammation induced by mucosal exposure to ethanol and acetic acid. We found that inflammation had no significant effect on in vivo and in vitro spontaneous or muscarinic receptor-mediated contractions of the longitudinal muscle. The longitudinal muscle contractions were mediated primarily by the M(3) receptor subtype. However, the IC(50) of the M(2) receptor antagonist methoctramine was only 10 times greater than that of the M(3) receptor antagonist 4-DAMP in the longitudinal muscle, whereas it was 224 times greater in the circular muscle. M(2) receptor-coupled decrease of intracellular cAMP occurred in the longitudinal but not in the circular muscle from the normal ileum. Inflammation did not alter this coupling in the longitudinal muscle but established it in the circular muscle. In conclusion, M(2) receptors may play a greater role in the mediation of longitudinal muscle contractions than circular muscle contractions. Inflammation does not alter the contractility or the relative role of muscarinic receptor subtypes in longitudinal muscle cells. However, it modulates the M(2) receptor coupling to adenylate cyclase in the circular muscle.

Characterization of enteric functional changes evoked by in vivo anti-CD3 T cell activation

Specific in vivo T cell activation initiated by treatment with anti-CD3 antibodies leads to diarrhea and structural damage of the intestinal mucosa. In this study, the effect of T cell-induced mucosal damage on jejunal epithelial ion transport, muscle contractility, and neuronal ACh release was assessed in Ussing chambers, organ baths, and a specialized perfusion apparatus, respectively. Time-matched control mice received hamster serum containing irrelevant antibodies. Jejunal segments from anti-CD3-treated mice displayed a significantly elevated epithelial baseline short-circuit current (which indicates increased ion transport) and a concomitant reduction in responsiveness to prosecretory stimuli (nerve stimulation, carbachol, and forskolin). Longitudinal smooth muscle displayed altered spontaneous contractile activity, length-tension relationships, and carbachol-stimulated contraction in tissues excised from mice 20 and 40 h posttreatment. Anti-CD3 treatment did not affect stimulated ACh release from myenteric plexus neurons. We conclude that specific T cell activation via anti-CD3 antibody results in dramatic alterations in jejunal epithelial and smooth muscle function. Such T cell-induced changes in intestinal function may contribute to the symptomatology of T cell-mediated enteropathies, including graft-versus-host disease, celiac disease, and idiopathic inflammatory bowel disease.

Gastrointestinal motility disorders in patients with inactive Crohn's disease

BACKGROUND

Although some symptoms of Crohn's disease may be related to gastrointestinal motility disorders, studies on gastrointestinal motility in inactive Crohn's disease are lacking.

METHODS

Fasting and postprandial motor activity (1 h) was recorded in the gastric antrum and upper small intestine of 35 patients with inactive Crohn's disease and 18 controls, using conventional manometry.

RESULTS

Motor disorders were observed in 26 of 35 patients. The number of phase-II contractions was reduced (1.3 +/- 0.7/min versus 1.8 +/- 0.6/min in controls; P < 0.02) (mean +/- standard deviation), whereas the incidence of propagated single (2.2 +/- 3.2/h versus 0.5 +/- 0.6/h; P < 0.03) and clustered contractions (3.8 +/- 7/h versus 1.1 +/- 1.4, P < 0.04) was markedly increased. Motor abnormalities were more frequent and severe in patients with Crohn's ileitis than in controls, and in patients with gastrointestinal symptoms than in asymptomatic patients.

CONCLUSION

Most patients with inactive, uncomplicated Crohn's disease show marked gastrointestinal motor disorders, characterized either by reduced incidence of small-bowel contractions and increased incidence of single or clustered propagated contractions.

Acute experimental colitis decreases colonic circular smooth muscle contractility in rats

Distal colitis decreases the contractility of the underlying circular smooth muscle. We examined how time after injury and lesion severity contribute to the decreased contractility and how colitis alters the calcium-handling properties of the affected muscle. Distal colitis was induced in rats by intrarectal administration of 4% acetic acid. Contractile responses to acetylcholine, increased extracellular potassium, and the G protein activator NaF were determined for circular muscle strips from sham control and colitic rats at days 1, 2, 3, 7, and 14 postenemas. Acetylcholine stimulation of tissues from day 3 colitic rats was performed in a zero calcium buffer, in the presence of nifedipine, and after depletion of intracellular stores of calcium. The colitis was graded macroscopically as mild, moderate, or severe. Regardless of agonist, maximal decrease in force developed 2 to 3 days posttreatment, followed by a gradual return to control by day 14. The inhibitory effect of colitis on contractility increased with increasing severity of inflammation. Limiting extracellular calcium influx had a greater inhibitory effect on tissues from colitic rats; intracellular calcium depletion had a greater inhibitory effect on tissues from control animals. The data suggest that both lesion severity and time after injury affect the contractile response of circular smooth muscle from the inflamed distal colon. Impaired utilization of intracellular calcium may contribute to the decreased contractility.

Characterisation of a postjunctional 5-ht7-like and a prejunctional 5-HT3 receptor mediating contraction of rat isolated jejunum

The 5-HT (5-hydroxytryptamine)-induced contractile biphasic concentration-effect curve in rat isolated jejunum was investigated. The pEC50 values for the first and second phases were 8.0 and 6.1, respectively. The responses were insensitive to atropine (0.1 microM), ketanserin (2 microM), (-)-pindolol (5 microM), yohimbine (0.1 microM) and GR 113808 ({1-[2-(methyl-sulphonylamino)ethyl]-4-piperidinyl}methyl 1-methyl-1 H-indole-3-carboxylate, 1 microM) but susceptible to cocaine (10 microM). The low affinity phase was blocked by tetrodotoxin (1 microM), ondansetron (1 microM) and SR48968 (S)-N-methyl-N-[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl]benzamide, 0.1 microM). The high affinity phase was antagonised non-surmountably by fluoxetine (1 microM) methysergide (0.1 microM), spiperone (0.1 microM) and methiothepin (0.1 microM). Ritanserin (0.01-0.1 microM) and mesulergine (0.01-0.1 microM) acted as surmountable, competitive antagonists with pA2 values of 8.0 and 8.1, respectively. Clozapine (0.1 microM) was a surmountable antagonist with an apparent pA2 value of 8.0. The rank potency order of the 5-HT receptor agonists was 5-CT (5-carboxyamidotryptamine) > or = 5-HT = 5-methoxytryptamine > or = alpha-methyl-5-HT > > 8-OH-DPAT ((+/-)-2-dipropyl-amino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene) > dipropyl-5-CT > renzapride = sumatriptan. The responses to 5-HT and 5-CT were not potentiated by pargyline (10 and 100 microM). It is suggested that rat jejunum contains a neuronal 5-HT3 receptor facilitating neurokinin release and a contractile smooth muscle 5-HT receptor with a pharmacological operational profile similar to the cloned 5-ht7 receptor.

On the specificity of altered muscle function in experimental colitis in rats

BACKGROUND

Studies on muscle contraction in colitis yield conflicting data that may reflect differences in the manner in which colitis is induced. Therefore, we compared distal colonic longitudinal muscle contraction in four models of colitis in the rat.

METHODS

Distal colitis was induced by intrarectal administration of trinitrobenzene sulfonic, acetic acid, or Trichinella spiralis larvae, or by intraperitoneal injection of mitomycin C. Colonic myeloperoxidase activity was used to monitor acute inflammation.

RESULTS

Myeloperoxidase activity increased in each model of colitis. In trinitrobenzene-treated rats, contractile responses to carbachol, substance P, and KCl decreased by 64%, 76%, and 58%, respectively. In acetic acid treated rats, responses induced by carbachol, substance P, or KCl were each significantly decreased by 73%, 68%, and 55% and were similarly reduced by 42%, 77%, and 46%, respectively, in rats with T. spiralis colitis. In mitomycin-induced colitis, these respective responses also decreased significantly by 71%, 55%, and 54%.

CONCLUSION

Decreased contractility of longitudinal muscle in acute colitis in rats is independent of the manner in which the colitis is induced and is mediated at a receptor-independent locus on the muscle cell.

Small intestinal motility and transit in disease

Disorders of small intestinal motility and transit are becoming increasingly recognized partly as a result of a greater awareness of their existence and partly because suitable diagnostic methods are more widely available. Usually, the neuropathic and myopathic forms can be separated, and gut disease secondary to a generalized neuromuscular disorder can be identified by the clinician. The availability of better non-invasive methods for the diagnosis of disorders of motility and transit would greatly facilitate their management. Treatment must include the restoration and maintenance of nutrition, attempts to improve intestinal motor function and resection of any segments of localized disease. Regrettably, all such measures are ineffective in the severest cases. In the future, a greater understanding of the enteric neural control of the smooth muscle and an ability to manipulate it with novel, specific drugs or peptidergic receptor agonists and antagonists, or electrical pacing, may lead to more effective therapies.

Jejunal circular muscle motility is decreased in nematode-infected rat

Jejunal circular muscle motility was studied in vitro in rats 8-10 days after inoculation with the inflammation-inducing nematode Nippostrongylus brasiliensis. The passive properties of the muscle, i.e., the development of passive tension and the optimal amount of stretch for active contractions, were unchanged by infection. Infection decreased the development of active resting tension, spontaneous contractions, muscle contraction to muscarinic receptor activation, and direct electrical stimulation. Relaxation to beta-adrenergic stimulation was also decreased in tissues from infected animals. Response to cholinergic stimulation, spontaneous contractions, and active resting tension were completely dependent on extracellular calcium. The dominant response to electrical stimulation of intrinsic nerves was relaxation in control tissue and contraction in tissue from infected rats. In the presence of atropine, all tissues from control rats but only 33% of the tissues from infected rats relaxed, suggesting a marked difference in functional inhibitory innervation. The inflammation may have either decreased the circular muscle responsiveness to the inhibitory transmitter or decreased the release of this transmitter. Thus, a nematode infection produces decreased responsiveness of the intestinal circular muscle to both contracting and relaxing stimuli and causes a reduction in functional inhibitory innervation in this layer. These changes suggest mechanisms for the reduction of intestinal transit observed after some nematode infections.

Neuropeptides, inflammation, and motility

Neurogenic inflammation is a reaction which includes vasodilation, plasma extravasation, and smooth muscle contraction elicited by activation of and release of mediators from unmyelinated afferent nerve endings. Further release of inflammatory mediators follows activation of axon collaterals associated with these afferent nerve endings as axon reflexes. Substance P, somatostatin, vasoactive intestinal polypeptide, and calcitonin gene-related peptide are candidate mediators. Recent evidence suggests that several of these peptides may be colocalized either with one or more other peptides or with acetylcholine or noradrenalin. Communicating pathways exist between nerves within the mucosa and the muscle layers. Both long and short visceral reflexes occur. Inflammatory, mechanical, or chemical stimuli reaching the mucosa may release peptides from peripheral nerve endings. Thus neurogenic inflammation may be an important factor in inflammatory bowel disease.

Antagonists and activators at calcium channels. Effects in the gastrointestinal tract

Most calcium antagonists have relatively minor effects in the gastrointestinal (GI) tract; the factors influencing drug selectivity are reviewed. Voltage-dependent Ca channels (VOCs) in GI smooth muscle appear to be essentially similar to those in the cardiovascular system in their sensitivity to calcium antagonists. However, selective conditions for channel activation may allow antagonists to be selective in certain disease conditions. Indirect effects on blood flow may be crucial to certain parameters (e.g., acid secretion). Activators of VOCs have similar effects in vascular and GI smooth muscle. Some endogenous activators of VOCs may exist and evidence for control of VOC activity by lipid metabolites is indicated. Acyl carnitines may function as endogenous activators of VOCs.