Abnormal mucus in cap polyposis

Background—Cap polyposis is a rare diseasecharacterised by mucoid and bloody diarrhoea, with polyps covered by acap of mucoid and fibrinopurulent exudate. The pathogenesis is not known.
Aims—To pour some light on cap polyposispathogenesis, by examining the mucus of patients and analysing theexpression of five mucin genes, MUC2, MUC3,MUC4, MUC5AC, and MUC5B.
Patient and methods—The study was performed onbiopsy specimens taken from a patient with recurrent cap polyposis.Histochemical examination, electron microscopy, and mRNA in situhybridisation were used.
Results—The mucus of cap polyposis differed inthree respects from that of normal adult colon: abnormal ultrastructureof the mucus in the goblet cells, predominance of non-sulphated mucins, abnormal expression of the MUC4, MUC3, andMUC5AC genes.
Conclusions—Most of these abnormalities have beenreported for other pathological situations, suggesting that theabnormalities observed in the mucus of this patient with cap polyposisare probably secondary phenomena rather than primary. However, themucin abnormalities detected, which reflect deregulation of theexpression of three apomucin genes, abnormal glycosylation, andabnormalities of the secretion process, are also probably involved inthe clinical manifestations of cap polyposis.

Keywords:cap polyposis; mucins; histochemistry; ultrastructure; in situ hybridisation

     

Altered Mucin Core Peptide Expression in Acute and Chronic Cholecystitis

Human mucin genes include membrane-bound mucins (MUC1, MUC3, MUC4) and secretory mucins (MUC2, MUC5AC, MUC5B, MUC6). Our aim was to determine mucin gene expression in human gallbladder cell lines, normal gallbladder from liver donors (N = 7) and surgical specimens with mild chronic cholecystitis (N = 29), chronic cholecystitis (N = 48), and acute and chronic cholecystitis (N = 27). MUC1 mRNA was ubiquitous; however, only rare MUC1 immunoreactivity was detected. MUC3, MUC5AC, MUC5B, and MUC6 mRNA were present in all gallbladder specimens and cell lines examined. Prominent MUC3, MUC5AC, MUC5B, and MUC6 immunoreactivity was present in 86–100% of normal gallbladders. The frequency of MUC5AC reactivity was decreased in specimens with acute cholecystitis (P < 0.05). In contrast, MUC2-reactivity was absent in normal gallbladder and present in 53.8% of acute cholecystitis specimens (P < 0.05). Surface epithelium is characterized by MUC3, MUC5AC, and MUC5B, whereas deeper mucosal folds display MUC5B and MUC6 immunoreactivity. Gallbladder epithelium demonstrates a unique and diverse pattern of mucin core proteins that becomes altered with increasing degrees of inflammation.     

Urokinase and the intestinal mucosa: evidence for a role in epithelial cell turnover

Background—The functions of urokinase inintestinal epithelia are unknown.
Aims—To determine the relation of urokinaseexpressed by intestinal epithelial cells to their position in thecrypt-villus/surface axis and of mucosal urokinase activity toepithelial proliferative kinetics in the distal colon.
Methods—Urokinase expression was examinedimmunohistochemically in human intestinal mucosa. Urokinase activitywas measured colorimetrically in epithelial cells isolated sequentiallyfrom the crypt-villus axis of the rat small intestine. In separate experiments, urokinase activity and epithelial kinetics (measured stathmokinetically) were measured in homogenates of distal colonic mucosa of 14 groups of eight rats fed diets known to alter epithelial turnover.
Results—From the crypt base, an ascendinggradient of expression and activity of urokinase was associated withthe epithelial cells. Median mucosal urokinase activities in each ofthe dietary groups of rats correlated positively with autologous mediannumber of metaphase arrests per crypt (r=0.68; p<0.005)and per 100 crypt cells (r=0.75; p<0.001), but not withcrypt column height.
Conclusions—Localisation of an enzyme capable ofleading to digestion of cell substratum in the region where cells areloosely attached to their basement membrane, and the association of its activity with indexes of cell turnover, suggest a role for urokinase infacilitating epithelial cell loss in the intestine.

Keywords:urokinase; intestinal epithelium; colon; epithelialproliferation

     

Expression of a marker for colonic crypt base cells is correlated with poor prognosis in human colorectal cancer

Background—There is a need for markers in colorectal cancer which will allow subclassification of stage groups into subgroups with high versus low risk of recurrent disease.
Aims—To develop monoclonal antibodies that recognise antigens on immature crypt base cells, on the assumption that in a neoplasm undifferentiated but not the terminally differentiated cells will be responsible for tumour progression.
Methods—Colon crypt cells which were isolated from human colonic mucosa by EDTA/EGTA incubation were studied. By stepwise harvesting, crypt base cell enriched fractions were obtained, and after incubation with antibodies against dominant antigens, used as immunogens.
Results—Of one crypt base cell specific antibody (5E9), the reactive epitope appeared to be a non-terminal carbohydrate in the mucin O-glycans of the colon. The epitope did not seem to be colon specific, but was expressed in a variety of other tissues. In colorectal carcinomas, 5E9 immunoreactivity identified a subgroup of patients with a tendency for worse prognosis.
Conclusion—A mucin associated maturation epitope was identified in colonic crypt base cells, the expression of which in Dukes'' stage B3 colorectal carcinoma may be associated with poor prognosis.

     

Interstitial cells of Cajal in the human fetal small bowel as shown by c-kit immunohistochemistry

Background—Interstitialcells of Cajal (ICCs) express the tyrosine kinase receptor c-kit, whichis required for their development and spontaneous pacemaker activity inthe bowel. From murine models it has been proposed that ICCs do notdevelop until after birth, but more recent findings indicate that c-kitis expressed early in the embryonic period. The temporal development ofICCs in the human gut remains unknown.
Aim—To investigateICCs in the human fetal small bowel using c-kit immunohistochemistry.
Subjects—Small bowelspecimens were obtained at post mortem examination of 16 fetuses andnine neonates, eight of whom were premature, born at gestational agesof 13 to 41 weeks, without gastrointestinal disorders.
Methods—Immunohistochemicalanalysis was performed on material fixed in formalin and embedded inparaffin. The specimens were exposed to antibodies raised against c-kit(an ICC marker) and neurone specific enolase (a general neuronalmarker). The ABC complex method was used to visualise binding ofantibodies to the corresponding antigens.
Results—c-kitimmunoreactive cells were visualised from 13 weeks of gestation. Theimmunoreactivity was mainly localised in association with the myentericplexus. From about 17-18 weeks of gestation, the ICCs formed a layeralong the myenteric plexus, whereas this layer appeared to be disruptedat 13-16 weeks of gestation.
Conclusions—ICCs arec-kit immunoreactive at least from a gestational age of 13 weeks inthe human fetal small intestine. From 17-18 weeks of gestation untilbirth, they form a continuous layer around the myenteric ganglia.

Keywords:interstitial cells of Cajal; c-kit; myentericplexus; human; fetal; development

     

Assembly and organization of the N-terminal region of mucin MUC5AC: Indications for structural and functional distinction from MUC5B

Elevated levels of MUC5AC, one of the major gel-forming mucins in the lungs, are closely associated with chronic obstructive lung diseases such as chronic bronchitis and asthma. It is not known, however, how the structure and/or gel-making properties of MUC5AC contribute to innate lung defense in health and drive the formation of stagnant mucus in disease. To understand this, here we studied the biophysical properties and macromolecular assembly of MUC5AC compared to MUC5B. To study each native mucin, we used Calu3 monomucin cultures that produced MUC5AC or MUC5B. To understand the macromolecular assembly of MUC5AC through N-terminal oligomerization, we expressed a recombinant whole N-terminal domain (5ACNT). Scanning electron microscopy and atomic force microscopy imaging indicated that the two mucins formed distinct networks on epithelial and experimental surfaces; MUC5B formed linear, infrequently branched multimers, whereas MUC5AC formed tightly organized networks with a high degree of branching. Quartz crystal microbalance-dissipation monitoring experiments indicated that MUC5AC bound significantly more to hydrophobic surfaces and was stiffer and more viscoelastic as compared to MUC5B. Light scattering analysis determined that 5ACNT primarily forms disulfide-linked covalent dimers and higher-order oligomers (i.e., trimers and tetramers). Selective proteolytic digestion of the central glycosylated region of the full-length molecule confirmed that MUC5AC forms dimers and higher-order oligomers through its N terminus. Collectively, the distinct N-terminal organization of MUC5AC may explain the more adhesive and unique viscoelastic properties of branched, highly networked MUC5AC gels. These properties may generate insight into why/how MUC5AC forms a static, “tethered” mucus layer in chronic muco-obstructive lung diseases.

Gel-forming mucins are an essential component of the mucus layer that covers and protects epithelial surfaces from environmental insults. The mucin composition of mucus lining different mucosal surfaces depends on the functional requirements imposed on the epithelium. For instance, in the small intestine and colon, which harbor diverse microbiota, MUC2 is the mucin structurally adapted to form a “tight mucus layer” that provides a niche for the microbes and protects the underlying epithelia by preventing bacterial invasion (1). While in the stomach, MUC6 and MUC5AC together provide a barrier that protects the epithelium from the harsh effects of high luminal acidity (pH = 2 to 3) (2). The mouth, which is the major portal of food and microbes, is protected by saliva, and the dominant gel-forming mucin is MUC5B (3). The lungs, another major portal with exposure to the environment, are mainly protected during homeostasis by MUC5B with a lesser contribution by MUC5AC (4, 5). The distinct regions of the airways have different functional and innate protective requirements for homeostasis, and this necessitates the diverse expression patterns of both mucins throughout the respiratory system (6). MUC5B, secreted by cells in the submucosal glands and the surface epithelium (6), has been shown to be essential for lung innate defense (7). MUC5AC, secreted only by cells in the surface epithelium mainly in the larger airways (6), is generally produced in response to stresses such as cigarette smoke and allergens and is closely associated with muco-obstructive lung diseases, including chronic bronchitis (CB), chronic obstructive pulmonary disease (COPD) (4, 8), and asthma (9, 10). MUC5AC is also critical for defense against enteric parasites, some of which invade the lung (11).Both MUC5B and MUC5AC are large (2 to 100 MDa), polymeric glycoproteins with a high degree of sequence similarity and domain homology, particularly in their N- and carboxyl- terminal regions (12–15). Similar to MUC5B, the N-terminal region of MUC5AC contains von Willebrand factor–like domains (D1, D2, and D3) in addition to trypsin inhibitory–like (TIL) domains and unique regions. The N terminus is followed by a central, highly O-glycosylated mucin domain, which is interrupted by cysteine-rich (CysD) domains and a carboxyl-terminal region that mediates dimerization. In contrast to other gel-forming mucins, MUC5AC contains a putative leucine zipper (LZ) domain (16) at the end of the carboxyl-terminal end of the D1 domain of the N terminus, with no known function.The major gel-forming mucins (MUC2, MUC5AC, MUC5B, and MUC6) assemble intracellularly to form polymers, first via disulfide-linked dimerization between their carboxyl termini and then via disulfide-linked N-terminal multimerization. However, knowledge of multimerization is incomplete. The MUC5B N-terminal region is assembled exclusively as dimers (17). However, assembly of the MUC2 N-terminal region is more controversial, and it has been reported to assemble solely as trimers (18) or dimers (19). The N-terminal assembly of MUC5AC has not been investigated. It is thought that the unique structural organization of the different gel-forming mucins results in mucus gels optimized to meet the functional demands and provide proper protection to the diverse epithelial environments across the body.MUC5AC mucin production is modulated by both type 1 [e.g., in response to viral infections (20, 21) and cigarette smoke (22)] and type 2 [e.g., in response to allergens (9)] immune responses, associated with lung disease and, indeed, disproportionately increases as compared to MUC5B (4, 8, 9, 23, 24). How MUC5AC contributes to both innate defense of the lung and the pathogenesis of chronic obstructive lung diseases remains unclear. As a first step of understanding the structural, organizational, and functionally distinctive properties of MUC5AC mucin and how these properties may affect the mucus gel organization/properties as compared to the other major lung mucin, MUC5B, we investigated the nature of MUC5AC multimeric organization through its N-terminal domain using an expressed recombinant protein (5ACNT), with a focus on the unique LZ region at the carboxyl-terminal end of the D1 domain. To understand if the LZ region has an organizational role in the assembly of the N-terminal region of MUC5AC, we mutated the four leucine residues in the LZ region of 5ACNT.     

Intracardiac pressures in the human fetus

OBJECTIVE—To obtain normal values for intracardiac pressures in the human
fetus.
DESIGN—Intracardiac pressures were measured directly in the four chambers of the human fetal heart during clinically indicated invasive obstetric procedures.
SETTING—Department of fetal medicine in a tertiary referral centre.
PATIENTS—39 fetuses between 16 and 29 weeks of gestation.
RESULTS—The ventricular waveforms obtained were similar to those found in postnatal life. There was an increase in ventricular systolic and end diastolic pressures with advancing gestation. There was no difference between left and right ventricular pressures. Atrial pressures were equal and remained constant in the gestational age range studied.
CONCLUSIONS—Fetal cardiovascular pressure measurements in the normal fetus assist in understanding the fetal circulation, and provide a basis for the assessment of cases of congenital heart disease that may be amenable to intrauterine treatment.


Keywords: fetus; ventricular pressure; congenital heart disease     

The role of xanthine oxidase in platelet activating factor induced intestinal injury in the rat

Background—Xanthine oxidase (XO) isan important source of reactive oxygen species in the small intestine.
Aims—To examine the interaction ofplatelet activating factor (PAF), XO, and neutrophils in mediatingintestinal injury in rats.
Methods—Two doses of PAF were usedto induce either reversible hypotension, or irreversible shock withintestinal necrosis. The activities of XO, and its precursor xanthinedehydrogenase (XD), in both the whole intestinal tissue and epithelialcells, were measured. XO was localised by histochemical staining.
Results—PAF dose dependentlyinduced an increase in XO activity, predominantly in the ilealepithelium, without altering the total activity of XD+XO. Most of theXD to XO conversion was via proteolysis. PAF induced XO activation andintestinal injury were prevented by prior neutrophil depletion. PAFinduced XO activation is probably not due to reperfusion, as XOactivation preceded the recovery of mesenteric flow. Allopurinolpretreatment substantially inhibited intestinal neutrophilsequestration induced by high dose (but not low dose) PAF.
Conclusions—PAF rapidly activatesintestinal XO through proteolytic XD-XO conversion, predominantly inthe ileal epithelium. This effect is mediated by neutrophils. XOactivation promotes PAF induced polymorphonuclear leucocytesequestration in the intestine.

Keywords:xanthine dehydrogenase; reactive oxygen species; leucocyte adhesion; neutrophils; shock

     

Human intestinal M cells exhibit enterocyte-like intermediate filaments

Background—The derivation and ultrastructuralcomposition of M cells covering the lymphoid follicles of Peyer'spatches is still unknown. Results from different animal models haveshown that there are species specific differences in the composition ofintermediate filaments between M cells and neighbouring enterocytes. Little is known, however, about intermediate filaments of human M cells.
Aims—To compare components of the cytoskeleton ofhuman M cells with those of adjacent absorptive enterocytes.
Methods—The expression and localisation ofdifferent cytokeratins, vimentin, and desmin in M cells was determinedon follicle associated epithelia of human appendix usingimmunohistochemistry and immunogold electron microscopy.
Results—Cytokeratins specific for humanintestinal epithelial cells such as cytokeratins 8, 18, 19, and 20 wereexpressed in both absorptive enterocytes and M cells with nodifferences in intensity and cellular distribution between both celltypes. Vimentin and desmin, tissue specific markers of eithermesenchymal or myogenic cells, as well as other cytokeratins were notdetectable in enterocytes or M cells.
Conclusion—This is the first study on thestructure of intermediate filaments in human intestinal M cells. Ourresults show that in contrast to several animal models, human M cellsapparently do not differ from adjacent enterocytes in the compositionof their intermediate filament cytoskeleton. The presence of enterocyte like cytokeratins and the absence of other cytokeratins as well as ofvimentin and desmin supports the hypothesis of an epithelial origin ofhuman intestinal M cells and suggests that M cells may derive fromdifferentiated enterocytes.

Keywords:human intestinal M cells; appendix; cytokeratin; intermediate filaments; follicle associated epithelium

     

Mast cell mediated ion transport in intestine from patients with and without inflammatory bowel disease

Background—Mast cells have been shown to regulateintestinal ion transport in animal models and normal human colon buttheir physiological role in human intestinal inflammatory disorders is unknown.
Aims—To examine mast cell regulation of iontransport in inflammatory bowel disease (IBD).
Subjects and methods—Small and large intestinewas obtained from patients with and without IBD undergoing surgicalresection. Short circuit current (Isc) responses to rabbitantihuman IgE, histamine, and electrical stimulation were measured inUssing chambers. Specimens were also examined for mast cell numbers and degree of inflammation.
Results—Isc responses to anti-IgEand histamine were smaller in magnitude in IBD compared with non-IBDtissues. In all tissues, anti-IgE Isc responses werereduced by about 80% in chloride free buffer. The histamineH₁ receptor antagonist, pyrilamine, decreased anti-IgEresponses in non-IBD tissues. Greater inhibition with pyrilamine wasseen in IBD small intestine but its effect was less in IBD colon.Histamine pretreatment of non-IBD control tissues reduced anti-IgEresponses to levels seen in IBD colon but had no effect in smallintestine. Mast cell numbers were greater in IBD compared with non-IBDsmall intestine while no differences were observed between the colonicgroups. Isc responses to anti-IgE were not correlated withthe degree of mucosal inflammation.
Conclusions—This study provides further evidencethat mast cells are capable of mediating alterations of ion transportin human gut but that this regulatory role may be altered in IBD. Thedata suggest that prior activation of mast cells with release ofhistamine may account for the reduced secretory response to anti-IgEobserved in IBD colonic tissues.

Keywords:mast cells; intestine; ion transport; histamine; ulcerative colitis; Crohn's disease

     

Kallikrein-kininogen system activation and bradykinin (B2) receptors in indomethacin induced enterocolitis in genetically susceptible Lewis rats

Background—The plasmakallikrein-kinin (K-K) system is activated in acute and chronicrelapsing intestinal inflammation induced in Lewis rats by intramuralinjection of exogenous bacterial components.
Aims—To determine whetherthis effect is model specific, K-K system activation was investigatedin a modified indomethacin induced enterocolitis model, as well asbradykinin 2 (B2) receptor distribution in the normal and acutelyinflamed intestine.
Methods—Lewis rats injected withdaily sublethal doses of indomethacin for two days developed acute (twodays) and chronic (14 days) intestinal inflammation. Plasmaprekallikrein (amidolytic), high molecular weight kininogen (HK,coagulant) and cleavage of HK (western blot) were assayed to detect K-K activation.
Results—Liver and spleen weightswere significantly higher, and body weights and haematocrit values weresignificantly lower in the indomethacin group than in the controlgroup. During both acute and chronic phases, rats displayed K-K systemactivation manifested by a significant decrease in plasma prekallikreinand HK functional levels, and by HK cleavage. Plasma T kininogen (a major acute phase protein) was significantly elevated. B2 receptors were identified in both normal and inflammatory intestine with moreprominent specific immunohistochemical staining in the acutely inflamed tissue.
Conclusions—K-K system activationoccurs in association with both acute and chronic phases of intestinalinjury, regardless of the triggering agent, suggesting that activationof this system is integrally involved in intestinal inflammation ingenetically susceptible hosts. Localisation of B2 receptors acrossintestinal layers provides a structural basis for the kinin function inthe intestine.

Keywords:plasma kallikrein; kininogen; bradykinin 2 receptor; enterocolitis; indomethacin; proteoglycan-polysaccharide

     

Mucin gene expression in Barrett's oesophagus: an in situ hybridisation and immunohistochemical study

BACKGROUND AND AIMS: Mucin genes are expressed in a site specific manner throughout the gastrointestinal tract. Little is known about the expression pattern in the oesophagus. In this study we have investigated MUC gene expression in both the normal oesophagus and specialised intestinal metaplasia (Barrett's oesophagus). PATIENTS: Archived paraffin embedded material from eight specimens of normal oesophagus, 18 Barrett's oesophagus, eight gastric metaplasia, six high grade dysplasia, and six cases of adenocarcinoma were examined for expression of the mucin genes MUC1-6. METHODS: Mucin mRNA was detected by in situ hybridisation using [(35)S] dATP labelled oligonucleotide probes. Mucin core protein was detected by immunohistochemistry. RESULTS: Normal oesophagus expressed MUC5B in the submucosal glands and MUC1 and MUC4 in the stratified squamous epithelium. Barrett's oesophagus strongly expressed MUC5AC and MUC3 in the superficial columnar epithelium, MUC2 in the goblet cells, and MUC6 in the glands. In high grade dysplasia and adenocarcinoma there was downregulation of MUC2, MUC3, MUC5AC, and MUC6, but upregulation of MUC1 and MUC4 in half of the specimens examined. CONCLUSIONS: Normal oesophagus and Barrett's oesophagus have a novel pattern of mucin gene expression. Barrett's oesophagus expressed the mucins associated with normal gastric epithelium and normal intestinal epithelium. While most mucin genes were downregulated in severely dysplastic and neoplastic tissues, there was upregulation of the membrane bound mucins MUC1 and MUC4. This may prove useful in detecting early signs of progression to adenocarcinoma of the oesophagus.     

Anti-inflammatory drugs and endothelial cell adhesion molecule expression in murine vascular beds

Background—Inflammatory boweldiseases (IBD) are characterised by an intense infiltration ofleucocytes that is mediated by adhesion molecules expressed on thesurface of activated endothelial cells.
Aims—To determine whether drugsused in the treatment of IBD, specifically dexamethasone (DEX),5-aminosalicylic acid (5-ASA), methotrexate (MTX), and 6-mercaptopurine(6-MP), alter the expression of endothelial cell adhesion molecules (ECAMs).
Methods—The expression ofP-selectin, E-selectin, intercellular adhesion molecule 1 (ICAM-1), andvascular CAM 1(VCAM-1) in different vascular beds of C57Bl/6J mice wasmeasured using the dual radiolabelled monoclonal antibody technique.
Results—Lipopolysaccharide (LPS)elicited a profound increase in the expression of all ECAMs in themesentery, small intestine, caecum, and distal colon. The LPS inducedincrease in CAM expression was not significantly affected by priortreatment with either MTX or 6-MP. However, pretreatment with eitherDEX or 5-ASA significantly attenuated LPS induced increases inexpression of P- and E-selectin, and VCAM-1 in the majority of tissuesevaluated. DEX also blunted the LPS induced increase in ICAM-1expression in the caecum and distal colon. DEX, but not 5-ASA, largelyabolished the rise in plasma tumour necrosis factor α elicited by LPS.
Conclusions—These findings suggestthat DEX and 5-ASA may exert their beneficial therapeutic action inIBD, at least in part, by inhibiting the expression of ECAMs whichmediate leucocyte adhesion and transmigration in the microvasculature.

     

Clonal analysis of isolated intestinal metaplastic glands of stomach using X linked polymorphism

Background—Monoclonal precancerous cells undergosuccessive biochemical and genetic changes during the multistep processof carcinogenesis in the gastrointestinal tract. Despite a highassociation with intestinal-type stomach cancer (differentiatedadenocarcinoma of the stomach), the role of intestinal metaplasia isunclear in stomach carcinogenesis.
Aims—To study the clonality of intestinal metaplasia.
Methods—The clonality of 86 single intestinalmetaplastic glands isolated by EDTA treatment from gastrectomyspecimens from patients with cancer were investigated. The methylationsensitive restriction enzyme HpaII and polymerase chainreaction (PCR) were used to detect a polymorphic human androgenreceptor gene locus linked to an inactive X chromosome.
Results—Forty one (48%) intestinal metaplasticglands were heterotypic (mixed cells of different allelic methylation)and 45 (52%) were homotypic (cell population of the same allelicmethylation), while almost all the single pyloric glands werehomotypic. Eleven of 13 intestinal metaplastic mucosae that were 6 mmin diameter contained glands that had originated from different cells.There were no strong relationships between clonal type and location orhistological type of intestinal metaplasia.
Conclusion—Intestinal metaplasia in general is nota lesion that arises or proceeds monoclonally.

     

Proabsorptive and prosecretory roles for nitric oxide in cholera toxin induced secretion

Background—Cholera toxin causessmall intestinal hypersecretion by inducing a coordinated response fromenterocytes, enterochromaffin cells, enteric neurones, and the vascularsupply. Nitric oxide has been implicated in the function of theseseparate components.
Aims—To explore the role of nitricoxide in the totality of cholera toxin induced secretion in vivo.
Methods—One group of adult maleWistar rats was treated with the nitric oxide synthase inhibitorsN^G-nitro-L-arginine methyl ester(L-NAME; subcutaneously or intraluminally), N^G-methyl-L-arginine (L-NMA), or7-nitroindazole. A second group of rats was treated withL-arginine (intraperitoneally or intraluminally) orD-arginine. The small intestine was isolated between twocannulae and instilled with 75 µg cholera toxin or saline for twohours. Small intestinal perfusion of a plasma electrolyte solutioncontaining [¹⁴C]-PEG was undertaken to determine netwater and electrolyte movement. After the experiment macroscopic andmicroscopic intestinal appearances were noted and jejunal5-hydroxytryptamine concentrations were determined.
Results—Both L-arginineand L-NAME induced secretion in the basal state, but onlywhen administered intraluminally. Systemically appliedL-NAME caused a dose dependent reduction in cholera toxininduced secretion. This was paralleled by L-NMA but not by7-nitroindazole or by intraluminally applied L-NAME. Systemically applied L-NAME caused notable cyanosis of theintestine, consistent with mesenteric ischaemia, but no microscopicabnormalities. Systemically applied L-arginine but notD-arginine also reduced cholera toxin induced secretion andinhibited 5-hydroxytryptamine release.
Conclusion—Nitric oxide has aduality of roles in cholera toxin induced secretion, acting both as anabsorbagogue and a secretagogue. Its mechanisms of action include themaintenance of mucosal perfusion and enterochromaffin cell stabilisation.

Keywords:cholera toxin; nitric oxide; smallintestinal transport; 5-hydroxytryptamine; L-arginine; nitric oxide synthase inhibitors

     

Antisecretory factor suppresses intestinal inflammation and hypersecretion

Background—Antisecretory factor (AF) is a recentlyidentified regulatory protein which inhibits the intestinal fluidsecretion induced by cholera toxin.
Aims—To test the effect of AF on: (a)inflammation and hypersecretion induced by toxin A fromClostridium difficile; and (b) morphologicalchanges and hypersecretion induced by okadaic acid (the blue musseltoxin) in rat intestinal mucosa.
Methods—Morphological changes and fluidaccumulation were observed in intestinal loops challenged with 1 µgof toxin A or 3 µg of okadaic acid administered beforeor after injection of 0.1 µg of recombinant AF (rAF).
Results—The cytotoxic and inflammatory reactioncaused by toxin A was abolished after treatment with rAF given eitherintraveneously or intraluminally prior to the toxin or one hour afterthe toxin. The intestinal fluid response induced by toxin A and okadaicacid was reduced 55-80% by rAF. However, the characteristic increase in goblet cells at the tips of villi in the okadaic acid treated mucosawas not inhibited by rAF.
Conclusion—Results suggest that AF might beinvolved in protection against inflammation and in counteractingdehydration caused by enterotoxins. Both effects are probably mediatedvia the enteric nervous system.

Keywords:okadaic acid; Clostridiumdifficile toxin A; diarrhoea; neuropeptide; S5a; rat

     

Lipids infused into the jejunum accelerate small intestinal transit but delay ileocolonic transit of solids and liquids

Background—Various nutrients areknown to alter small intestinal motility patterns although their effecton transit of fluids and solids in man is not clear.
Aims—To determine small intestinaltransit of solids and liquids during perfusion with lipids, protein,and non-energy solutions.
Methods—Twenty eight healthyvolunteers received a jejunal infusion (1 ml/ minute for 30 minutes) ofone of four solutions: a lipid or a protein solution (4.18 J/ml), anon-absorbable electrolyte solution containing polyethylene glycol, or0.9% sodium chloride. As solid phase marker 1 g of amberlite resinpellets labelled with ¹¹¹InCl₃ was added;^99mTc DTPA was used as a fluid phase marker. Images wereobtained on a gamma camera at 10 minute intervals for four hours oruntil all radiolabel was detected in the colon.
Results—Intestinal transit ofsolids and liquids from the duodenojejunal junction to the caecum wassimultaneous, and independent of the energy content of the solutioninfused. Lipid infusion accelerated transit through the small intestinebut delayed transport of chyme along the ileocolonic junction. Afterprotein small intestinal transit was slowest; ileocolonic transit onthe other hand was fastest with protein. Transit of the non-energysolutions was in between that of the nutrient solutions.
Conclusions—Transit times throughthe small intestine and the ileocolonic junction were influenced by theluminal contents. In the small intestine fat induced significantlyfaster transit compared with proteins, but delayed ileocolonic transit.Once in the small intestine, solids and liquids transit the small bowel together, independent of the luminal content.

Keywords:small intestine; ileocolonic junction; transit; nutrients; lipids; proteins