The role of IL-4 in Heligmosomoides polygyrus-induced alterations in murine intestinal epithelial cell function.

IL-4 and IL-13 promote gastrointestinal worm expulsion, at least in part, through effects on nonlymphoid cells, such as intestinal epithelial cells. The role of IL-4/IL-13 in the regulation of intestinal epithelial function during Heligmosomoides polygyrus (Hp) infection was investigated in BALB/c mice infected with Hp or treated with a long-lasting formulation of recombinant mouse IL-4/alphaIL-4 complexes (IL-4C) for 7 days. Separate groups of BALB/c mice were drug-cured of initial infection and later reinfected and treated with anti-IL-4R mAb, an antagonist of IL-4 and IL-13 receptor binding, or with a control mAb. Segments of jejunum were mounted in Ussing chambers, and short circuit current responses to acetylcholine, histamine, serotonin, PGE2, and glucose were determined. Although only modest changes in epithelial cell function were observed during primary Hp infection, IL-4C or a secondary Hp infection each induced more dramatic changes, including increased mucosal permeability, reduced sodium-linked glucose absorption, and increased Cl- secretory response to PGE2. Some, but not all, effects of IL-4C and Hp infection were dependent on enteric nerves. Hp-induced changes in epithelial function were attenuated or prevented by anti-IL-4R mAb. Thus, IL-4/IL-13 mediate many of the effects of Hp infection on intestinal epithelial cell function and do so both through direct effects on epithelial cells and through indirect, enteric nerve-mediated prosecretory effects. These immune system-independent effector functions of IL-4/IL-13 may be important for host protection against gastrointestinal nematodes.

Human colonic anti-secretory activity of the potent NK(1) antagonist, SR140333: assessment of potential anti-diarrhoeal activity in food allergy and inflammatory bowel disease.

1. This in vitro study was designed to determine the potential use of the NK(1) antagonist, SR140333 as an anti-diarrhoeal treatment for food allergy or inflammatory bowel disease. The effect of various immune and neuronal stimuli on human colonic substance P (SP) release and the effect of SR140333 on subsequently stimulated mucosal ion transport was investigated. 2. Submucosal and sensory nerve fibre stimulation using electrical field stimulation (1 ms/7 Hz/7 V) and capsaicin (50 microM) respectively, mast cell activation by anti-IgE (1/250 dilution) and granulocyte stimulation using fMLP (50 microM) each released SP and evoked a secretory response. 3. SP and the NK(1) selective agonist, Sar-SP (0.1 - 1000 nM) stimulated an increase in colonic secretion which was antagonized by SR140333 (pD'(2)=6.7 and 7.25 versus SP and Sar-SP respectively). 4. SR140333, at a concentration that blocked NK(1)-mediated secretion (500 nM), also reduced the secretory response to both alphaIgE and capsaicin. This suggests a pathophysiologic role for NK(1) receptors. 5. Capsaicin evoked SP release was increased in tissue taken from Crohn's disease but not ulcerative colitis patients. The response to SP was however reduced by 70 and 89% respectively. 6. Mast cells and sensory afferents contribute to allergic diarrhoea. Since SR140333 reduced the secretory response to mast cell and afferent stimulation this compound may be particularly useful in reducing the symptoms of food allergy.

Potent NK1 antagonism by SR-140333 reduces rat colonic secretory response to immunocyte activation.

The potent neurokinin receptor 1 (NK1) antagonist SR-140333 has previously been shown to reduce castor oil-induced secretion in animal models. The importance of tachykinins in neuroimmune control of secretion and the effect of SR-140333 on key points in this pathway were elucidated in the present study to determine the type of intestinal dysfunction best targeted by this antagonist. Rat colonic secretion and substance P (SP) release were determined in vitro with the use of Ussing chamber and enzyme immunoassay techniques. NK1 receptors played a secretory role as receptor agonists stimulated secretion and SR-140333 antagonized the response to SP response (pK(b) = 9.2). Sensory fiber stimulation released SP and evoked a large secretion that was reduced by 69% in the presence of SR-140333 (10 nM). Likewise, mastocytes also released SP. The subsequent secretory response was reduced by 43% in the presence of SR-140333 (50 nM). SP was also released from granulocytes; however, this did not cause secretion. Functional NK3 receptors were present in the colon as senktide stimulated secretion, an effect that was increased during stress. We conclude that NK3 receptors may play a role in stress-related disorders, whereas NK1 receptors are more important in mast cell/afferent-mediated secretion.

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.

Antisecretory and relaxatory effects of tachykinin antagonists in the guinea-pig intestinal tract.

Existing models used to study the mechanism of action and antagonism of tachykinergic effects on intestinal contraction and secretion suffer from technical problems and have not been fully characterized using specific tachykinin antagonists. Contraction of ileal segments by substance P, colonic circular muscle by beta-alanine-neurokinin A, and longitudinal muscle by senktide were used as models for neurokinin-induced contraction in the guinea-pig. Guinea-pig colonic epithelial tissue was stimulated by substance P and senktide to assess NK1- and NK3-mediated secretion. Using these models the potency of therapeutically useful compounds was determined. NK1 and NK2 activation directly contracted smooth muscle, while NK1-mediated secretion was nerve-mediated. NK3 stimulation of contraction and secretion was neurally mediated, involving cholinergic nerves and 5-HT release. NK1-mediated contraction and secretion were antagonized by SR140333 (pD'2 = 9.29 and pKb = 8.53); NK2-mediated contraction was antagonised by SR48968 (pD'2 = 8.35) and NK3-mediated contraction and secretion were antagonized by SB223412 (pKb = 8.97 and 8.79). The mixed antagonist MDL103392 blocked NK1- and NK2-mediated contraction with pKb values of 7.92 and 6.71 respectively and NK1-mediated secretion with a pKb value of 6.57. This data characterizes existing tachykinin antagonists, and should orientate the development of improved compounds as therapies for intestinal disease.

Hyperthermia prevents functional, histological and biochemical abnormalities induced during ileitis.

Inflammatory bowel disease is associated with altered intestinal motility and epithelial damage. Hyperthermia induces heat shock protein expression, components of a basic cellular defence mechanism, and consequently prevents ischaemic damage. Here we investigate whether hyperthermia may prevent altered smooth muscle function as well as underlying inflammation in a model of inflammatory bowel disease. Ileal heat shock protein expression was induced in rats by hyperthermic shock (41.5 degrees C; 5 min). Two hours after heating or sham treatment, ileitis was evoked by TNBS. Ileal samples were taken 4 h later to determine the contractile response of circular muscle strips, and to measure heat shock protein expression, LTB4 generation and damage/inflammation. Ileitis was associated with an increase in the contractile response of circular muscle to substance P but not neurokinin A or nerve stimulation. Hyperthermia induced heat shock protein expression and also prevented this functional change as well as TNBS-induced LTB4 production, subsequent infiltration of neutrophils and epithelial damage. Thus, intestinal inflammation is associated with alterations in tachykinergic control of smooth muscle as well as inflammatory changes. Hyperthermia prevents these changes and induces heat shock protein expression. Pharmacological induction of these proteins may offer a novel clinical strategy in treating both of these aspects of disease.

The response of rat colonic mucosa to 5-hydroxytryptamine in health and following restraint stress.

The present study characterized the rat colonic secretory response to 5-hydroxytryptamine (5-HT) and determined alterations in this response following stress. 5-HT stimulated rat colonic short-circuit current in a concentration-dependent fashion (pD2 = 5.19). This response was subject to desensitization and was mimicked by the indolealkylamines with a rank order potency of 5-HT approximately alpha-methyl-5-HT > 5-carboxytryptamine approximately 5-methoxytryptamine. 2-Methyl-5-HT was a partial agonist. The colonic response to 5-HT was unaltered by methysergide (10 microM), ritanserin (0.1 microM), ondansetron (1 microM) or clozapine (10 microM), but was antagonized by the 5-HT4 receptor antagonists SB204070 (pD'2 = 9.32), GR113808 (pKb = 8.56), DAU6285 (pKb = 6.07) and SDZ205557 (pKb = 6.80). The response of colonic epithelial and oesophageal tunica muscularis mucosae to 5-HT is therefore mediated by a similar 5-HT4 receptor. Following wrap restraint stress, the colonic response to 5-HT became bimodal. Half of the preparations were hyper-responsive, while the rest were hypo-responsive to 5-HT. This 5-HT4 receptor may therefore be involved in stress related changes in fluid transport.

Effect of mizolastine on visceral sensory afferent sensitivity and inflammation during experimental colitis.

In the present study the effect of mizolastine (CAS 108612-45-9, SL85.0324-00) a novel potent histamine H1-receptor antagonist, on 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis, a rat model of inflammatory bowel disease, was investigated to determine whether mizolastine has anti-inflammatory properties. Treatment with TNBS resulted in increased nociception in response to rectal balloon distension and caused intestinal damage, tissue oedema and inflammation. Oral mizolastine (0.03-3.00 mg/kg given 1 h before and once daily for 3 days after TNBS treatment) significantly (p < 0.05) reduced nociception (49% at 0.3 mg/kg), gross intestinal damage (78% at 3.0 mg/kg), histological damage (54% at 3.0 mg/kg), intestinal tissue weight (69% at 3.0 mg/kg) and myeloperoxidase activity (66% at 3.0 mg/kg). In contrast, the H1-receptor antagonist terfenadine tested under the same experimental conditions at 3-30 mg/kg was without significant effect. It is concluded that, in addition to its antiallergic properties, mizolastine possesses anti-inflammatory actions that may not be related to its H1-receptor blocking properties, reducing sensory afferent hypersensitivity, damage and neutrophil infiltration observed during colitis.

Mechanism of tachykinin NK3 receptor-mediated colonic ion transport in the guinea pig.

The guinea pig colon was used to elucidate the mechanism of tachykinin-induced secretion. Increased short-circuit current was observed in response to natural and synthetic tachykinins with rank orders of potency of substance P > neurokinin A = neuropeptide K>> neuropeptide gamma; and senktide (tachykinin NK3 receptor agonist)> Sar-substance P (tachykinin NK1 receptor agonist)> betaAlaneurokinin A (tachykinin NK2 receptor agonist)). A functional role of tachykinin NK1 receptors was confirmed as substance P and neurokinin A responsiveness was blocked by the tachykinin NK1 receptor antagonist GR82334. The tachykinin NK3 receptor antagonist SB222200 had no effect, leaving in doubt the identity of the natural tachykinin NK3 receptor ligand in the colon. The response to tachykinin NK3 receptor activation was abolished by tetrodotoxin and predominantly due to atropine sensitive cholinergic activation. The non-cholinergic component resulted from stimulation of tachykinin NK 1 and 5-HT receptors as the response to senktide was blocked by GR82334 and tropisetron. In conclusion, tachykinin NK3 receptor activation stimulates cholinergic and non-cholinergic (tachykinin NK1-receptor and serotonin-mediated) secretory pathways.

Tachykinergic neurotransmission is enhanced in small intestinal circular muscle in a rabbit model of inflammation.

Previous electrophysiological studies have shown that tachykinin-mediated excitatory junction potentials are enhanced in a ricin model of inflammatory bowel disease. The present study extends these findings by investigating the contractile response to stimulation of noncholinergic nerves and tachykinin agonists. According to rank order potencies, the rabbit ileal circular muscle was neurokinin (NK)1 preferring, and the response to these agonists was down-regulated by acetylcholine and up-regulated by nitric oxide. In ricin-treated tissue, cholinergic and nitridergic modulation was lost; in the presence of atropine and N-nitro-L-arginine methyl ester, or tetrodotoxin, the response to NK1 and NK2 agonists was enhanced. The noncholinergic response to nerve stimulation was predominantly mediated by NK1 receptors, and the enhanced response of ricin-treated tissue to NK1 agonists probably contributes to the increased response to electrical field stimulation observed under these conditions. Increased tachykinin response and loss of control of this response by acetylcholine and nitric oxide are likely to have profound effects on intestinal motility and could contribute to some of the symptomology of inflammatory bowel disease.

Role of sensory afferents in the myoelectric response to acute enteric inflammation in the rabbit.

The role of sensory afferents in inflammation-induced alterations in myoelectric activity in vivo was investigated in the rabbit small intestine. Isolated ileal loops were implanted with serosal electrodes and exposed to ricin or vehicle after pretreatment with 125 mg/kg of subcutaneous (125 mg over 3 days) or intraluminal (640 microM) capsaicin. After 5 h of myoelectric recording, the loops were prepared for histology and for ex vivo generation of eicosanoids. Capsaicin exacerbated mucosal damage after exposure to ricin but did not alter neutrophil infiltration. Subcutaneous capsaicin alone elevated slow-wave frequency and spike events and transiently suppressed the myoelectric response to ricin. In contrast, intraluminal capsaicin alone did not alter myoelectric activity but produced a sustained inhibition of the response to ricin. Eicosanoid production was unchanged by capsaicin alone. Intraluminal capsaicin blocked increases in leukotriene C4 and prostaglandin E2 during inflammation, an effect that paralleled its inhibition of myoelectric activity. Thus the contribution of sensory afferents to altered motility during acute ileitis involves the release of mucosal inflammatory mediators that influence neural control of smooth muscle.

Interleukin-4 modulates cholinergic neural control of mouse small intestinal longitudinal muscle.

Interleukin-4 contributes to expulsion of certain gastrointestinal parasites and causes intestinal mucosal mastocytosis. Because mast cell-derived mediators are spasmogenic, potentially causing parasitic expulsion, we investigated the effect of interleukin-4 on smooth muscle and the mast cell and mediator dependency of this effect. BALB/c, mast cell-deficient W/Wv mice, 5-lipoxygenase-efficient mice, and their littermate controls were injected with interleukin-4-anti-interleukin-4 antibody complexes that chronically increase serum interleukin-4 levels. Mid-small intestinal segments, hung longitudinally in organ baths, were stimulated electrically or by agonists. The cholinergic response to electrical field stimulation was significantly increased by interleukin-4 treatment in BALB/c but not W/Wv mice. The enhanced cholinergic contraction was not due to increased acetylcholine responsiveness but was dependent on leukotriene D4, since it was reversed by leukotriene D4 receptor antagonism, and not observed in 5-lipoxygenase knock-out mice. Leukotriene D4 responsiveness was unaffected by interleukin-4 treatment. We conclude that interleukin-4 amplifies cholinergic excitation through a mast cell and leukotriene D4-dependent mechanism.

Post-synaptic 5-HT4 receptor modulation of tachykinergic excitation of rat oesophageal tunica muscularis mucosae.

Interaction between the 5-HT4 receptor and cholinergic-dependent and -independent contraction of the rat oesophageal muscularis mucosae was determined. Substance P- (in the presence of atropine) and carbachol-precontracted tissue was relaxed by tryptamines and the substituted benzamides with the following rank order of potency: 5-HT > 5-methoxytryptamine > cisapride > (R)-zacopride > lintopride > metoclopramide, consistent with 5-HT4 receptor activation. The response to 5-HT was not antagonized by tetrodotoxin, methysergide or ondansetron; but was shifted to the right by GR113808 ([1-[2-[methylsulphonyl)amino]ethyl]-4-piperidinyl]methyl-1-H- indole-3-carboxylate) in substance P- and carbachol-precontracted tissue, confirming 5-HT4-mediated relaxation. This study shows for the first time that although 5-HT4 receptors are involved in the modulation of cholinergic neurotransmission they can also act independently of this system modulating tachykinergic responsiveness.

Induction of the heat shock response prevents tissue injury during acute inflammation of the rat ileum.

OBJECTIVES: To determine if prior total body hyperthermia protected against subsequent acute ileitis induced by the cytotoxic lectin, ricin, in rats. The time course of heat shock mRNA and protein expression in the ileum was determined. The effects of heat stress on small intestinal mucosal integrity, arachidonic acid metabolism, and neutrophilic infiltrate were compared in heated and nonheated rats receiving vehicle or ricin intraluminally. The effect of hyperthermia on the circulating neutrophil superoxide production was also evaluated. DESIGN: Prospective, randomized, controlled trial. SETTING: University research laboratory. SUBJECTS: Forty-one adult, male Sprague-Dawley rats, weighing 150 to 250 g, and 32 adult, inbred, male Fisher 344 rats, weighing 175 to 250 g. INTERVENTIONS: Exposure to whole body hyperthermia and production of acute ileitis. Sprague-Dawley rats were divided randomly into four experimental groups: nonheated control group, heated control group, nonheated ricin group (1 mg/mL water, intraluminal), and heated ricin group. Sprague-Dawley rats in a separate study were assigned to seven groups based on the time of removal of the terminal ileum following hyperthermia: 0 min, or 1, 2, 4, 8, 12, and 24 hrs. Inbred Fisher 344 rats were allocated to the heated and nonheated groups for peripheral neutrophil superoxide generation studies. MEASUREMENTS AND MAIN RESULTS: Whole body hyperthermia to a rectal temperature of 41 degrees C to 42 degrees C for 15 to 20 mins: a) was associated with marked mucosal cytoprotection against subsequent ricin-induced ileitis (Injury grade [from 0 = normal to 5 = severe]: 0.4 +/- 0.1 vs. 2.5 +/- 0.2, p < .001); b) prevented the ricin-induced reduction in villus height to crypt depth ratio (2.4 +/- 0.1 vs. 1.9 +/- 0.1, p < .01); and c) significantly reduced the number of infiltrating neutrophils when compared with nonheated ricin-treated rats (11 +/- 2 vs. 32 +/- 3 neutrophils/high-power field, p < .001). The hyperthermia-induced peak increase in heat shock protein (HSP)-70 mRNA at 2 hrs preceded that of HSP 70i at 4 hrs. Heat shock significantly reduced the ricin-induced increase in both basal (8.0 +/- 1.9 vs. 33.0 +/- 8.1 pg of leukotriene B4/mg protein, p < .05) and ionophore-stimulated (16.0 +/- 4.9 vs. 80.0 +/- 15.5 pg of leukotriene B4/mg protein, p < .001) generation of ileal leukotriene B4, but did not alter the cyclooxygenase product, prostaglandin E2. Hyperthermia did not alter peripheral neutrophil superoxide production. CONCLUSIONS: This study assessed the effects of heat shock in the normal and acutely inflamed intestine. These data suggest that heat stress and increased expression of HSP 70i protect against acute intestinal inflammation. This protection is associated with significant reductions in ileal leukotriene B4 generation and neutrophilic infiltrate. Hyperthermia did not alter circulating neutrophil superoxide production. Thus, the mechanism of heat stress protection against acute ileitis may involve local intestinal inhibition of leukotriene B4 production and subsequent neutrophilic infiltration without altering the ability of systemic neutrophils to be activated.

Cytokine regulation of host defense against parasitic gastrointestinal nematodes: lessons from studies with rodent models.

Studies with rodents infected with Trichinella spiralis, Heligmosomoides polygyrus, Nippostronglyus brasiliensis, and Trichuris muris have provided considerable information about immune mechanisms that protect against parasitic gastrointestinal nematodes. Four generalizations can be made: 1. CD4+ T cells are critical for host protection; 2. IL-12 and IFN-gamma inhibit protective immunity; 3. IL-4 can: (a) be required for host protection, (b) limit severity of infection, or (c) induce redundant protective mechanisms; and 4. Some cytokines that are stereotypically produced in response to gastrointestinal nematode infections fail to enhance host protection against some of the parasites that elicit their production. Host protection is redundant at two levels: 1. IL-4 has multiple effects on the immune system and on gut physiology (discussed in this review), more than one of which may protect against a particular parasite; and 2. IL-4 is often only one of multiple stimuli that can induce protection. Hosts may have evolved the ability to recognize features that characterize parasitic gastrointestinal nematodes as a class as triggers for a stereotypic cytokine response, but not the ability to distinguish features of individual parasites as stimuli for more specific protective cytokine responses. As a result, hosts deploy a set of defense mechanisms against these parasites that together control infection by most members of that class, even though a specific defense mechanism may not be required to defend against a particular parasite and may even damage a host infected with that parasite.

Local TH1 and TH2 responses to parasitic infection in the intestine: regulation by IFN-gamma and IL-4.

Control of parasitic infections is dependent on the production of cytokines that activate mechanisms which limit invasion, reproduction or survival of the parasite. In contrast, conditions that induce inappropriate cytokine responses facilitate the spread of infection and ultimately exacerbate the level of disease. Measurement of local cytokine responses to different gastrointestinal parasites, such as the intracellular protozoan, Cryptosporidium parvum, and luminal dwelling nematodes like Nippostrongylus brasiliensis and Heligmosomoides polygyrus, reveal stereotype response patterns. In general, intracellular parasites stimulate type 1 responses where IFN-gamma is the predominant immune activator, while extracellular parasites stimulate type 2 responses where IL-4 plays a prominent role in elevating humoral immune mechanisms. Cytokines alter cellular function and the milieu of the intestinal lumen to affect the outcome of an infection. The importance of a particular response during the course of an infection can be studied by selective enhancement with an excess of exogenous recombinant cytokine or cytokine antagonists. For example, exogenous IL-12 enhances resistance to C.parvum, but suppresses the normally rapid cure of an infection with N. brasiliensis. Both mechanisms are dependent on expression of IFN-gamma. At the molecular level, exogenous IL-12 stimulates IFN-gamma production which elevates a protective type 1 response to C. parvum but converts the normally anti-worm type 2 response to a type 1 response that inappropriately regulates the infection. Alternatively, excess IL-4 plays a prominent role in modulating effector elements that change intestinal physiology to create a hostile environment for worm parasites. Exogenous IL-4 can cure chronic worm infection, while IL-4 antagonists interfere with protective responses to infection. These observations provide a paradigm for analysis of stereotype responses to different gastrointestinal parasites, and demonstrate how cytokine-induced immune system-dependent and independent effector mechanisms can limit parasitic infection, while inappropriate cytokine responses can exacerbate the state of disease.

Effects of antibiotics on epithelial ion transport in the rabbit distal colon in-vitro.

One side-effect of the therapeutic use of antimicrobial agents is respiratory paralysis as a result of inhibition of skeletal neuromuscular transmission; cholinergic neuro-effector motor transmission in the gastrointestinal tract is inhibited by the same classes of antimicrobial agent. Study of the effects of several classes of antibiotic compound on intestinal motility has suggested that antibiotic-induced alterations of intestinal motility may be related to the onset of diarrhoea or the development of antibiotic-associated colitis. These compounds may, however, also initiate or exacerbate diarrhoea by altering control of epithelial function, a possibility that has not previously been rigorously investigated. This series of experiments investigated the effect of six antibiotics on rabbit distal colonic epithelial ion transport. Of all the antibiotics studied, only ampicillin was without effect. Clindamycin, erythromycin, gentamicin and lincomycin, each reduced the response of the epithelium to electrical field stimulation. In addition, the lincosamides clindamycin and lincomycin reduced basal short circuit current and the epithelial response to acetylcholine. Vancomycin had no effect on the response to electrical field stimulation or acetylcholine but enhanced the secretory action of prostaglandin E2. These data suggest that, in addition to their ability to alter intestinal motility, a number of potential antibiotic interactions with the epithelium and its innervation may contribute to the pathogenesis of antibiotic-associated diarrhoea and colitis.

Neural control of mouse small intestinal longitudinal muscle: interactions with inflammatory mediators.

The present study was undertaken to investigate neural control of mouse small intestinal longitudinal muscle. Electrical field stimulation evoked acetylcholine- and neurokinin A-mediated contractile responses, whereas nitric oxide-mediated neurotransmission resulted in relaxation. The inflammatory mediators, histamine and leukotriene D4, contracted the longitudinal muscle preparation. Histamine-evoked contractions resulted from binding to histamine H1 receptors on non-neural cells of the small intestine. Leukotriene D4 played a role in neurokinin A-mediated excitation as the leukotriene D4 receptor antagonist, WY 48,252, reduced the response to nerve stimulation under noncholinergic conditions by almost 80%. In contrast, WY 48,252 had no effect on the response to exogenous neurokinin A, indicating that the response to this neurotransmitter is not mediated by leukotriene D4 release. Subthreshold concentrations of leukotriene D4 did not modify the response to neurokinin A, ruling out a synergistic relationship between these two agonists. Leukotriene D4 did not cause synaptic transmitter release through ganglionic stimulation, because its contractile effect was tetrodotoxin insensitive, and did not contribute to noncholinergic excitation through stimulation of neurokinin A release, as the neurokinin2 receptor antagonist, MEN 10,376, did not alter the response to leukotriene D4. Instead leukotriene D4 may modulate the release of neurokinin A from nerve endings during nerve stimulation.

Changes in enteric neural regulation of smooth muscle in a rabbit model of small intestinal inflammation.

In vitro electrophysiological studies of ileal circular muscle from rabbits with ricin-induced inflammation were performed to investigate whether altered neural control or myogenic activity contributes to previously described changes in in vivo myoelectric activity. Ricin treatment increased mean slow-wave amplitude but not frequency or resting membrane potential. Prolonged electrical field stimulation evoked a hyperpolarization during the stimulus train and a depolarization on cessation of stimulation. In the presence of atropine, the depolarization was larger in ricin-treated tissue than in control tissue, showing that ileitis enhanced noncholinergic excitation. The nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester reduced the hyperpolarization in ricin-treated but not in control tissue, suggesting that inflammation increased nitric oxide-mediated inhibition. Substance P desensitization reduced noncholinergic excitation and mean slow-wave amplitude only in ricin-treated tissue, demonstrating that changes in these parameters during inflammation resulted from increased release of, or sensitivity to, tachykinins. These data suggest that acute ileitis alters tachykinin- and nitric oxide-mediated neurotransmission that may affect the normal pattern of ileal motility and/or sensory reflexes.

Effects of rotavirus on epithelial transport in rabbit small intestine.

The present study investigated changes in small intestinal epithelial transport in rabbits infected with rotavirus. The crypt depth-villus height ratio was increased in infected ileal tissue as a result of a significant increase in crypt depth and patchy shortening of the villi. Similar villus damage was seen in the jejunum. Despite these histological changes, basal fluid absorption by both the ileum and jejunum of infected animals was unaltered. Values for basal short-circuit current and resistance were similar; however, the increase in short-circuit current evoked by prostaglandin E2 was significantly smaller in rotavirus-infected tissues than in controls. The apparent Vmax for electrogenic glucose and alanine uptake by the jejunum was significantly increased following inoculation with rotavirus. Reduced responsiveness to the secretory effect of prostaglandin E2 and increased nutrient uptake may limit diarrhea that would otherwise be expected to occur as a result of the changes in mucosal architecture. This has important implications on the clinical treatment of rotavirus diarrhea, suggesting that oral rehydration therapy, which depends on the active transport of nutrients, may provide a more effective treatment than the use of cyclooxygenase inhibitors.