Interleukin-8 increases acetylcholine response of rat intestinal segments.

BACKGROUND: Interleukin-8 (IL-8) is a pro-inflammatory cytokine highly expressed in inflammatory bowel diseases, but whose effects on intestinal motility are unknown. AIM: To characterize the role of IL-8 in the contraction of rat intestinal segments. METHODS: Contractile response to acetylcholine (ACh 10-6 M) in terminal ileal segments (including mucosa) from Wistar rats was measured before and after incubation (15, 30, 60 or 90 min) with IL-8 (1 ng/mL), and after 60 min of incubation with different doses of IL-8 (0, 0.1, 0.5, 1, 10 and 100 ng/mL). The effects of blocking neural transmission with tetrodotoxin (TTX) and inhibiting protein synthesis (cycloheximide) were tested. The contractile response of longitudinal muscle-myenteric plexus preparations (i.e. without mucosa) was measured after 60 min of incubation with 0.1 and 1 ng/mL of IL-8. RESULTS: IL-8 increased ileal contraction induced by ACh 10(-6) M. This augmentation was significant after 60 min of incubation (58%, P=0.01) and persisted after 90 min (18%, P=0.04). A 60-min incubation period showed a dose-related effect, beginning at 0.5 ng/mL (30%, P=0.003) and reaching a peak at 1 ng/mL (58%, P=0.01). The same effect was also observed on colonic segments. TTX did not affect the IL-8 increase of ACh-induced contractions, which was completely abolished by cycloheximide. IL-8 had no significant effect on longitudinal muscle-myenteric plexus preparations. CONCLUSION: In vitro, IL-8 increases contractile response of the ileum to ACh in a dose-dependent manner. This effect is not neurally mediated, but seems to involve protein synthesis by intestinal mucosa.

Altered myoelectrical activity in noninflamed ileum of rats with colitis induced by trinitrobenzene sulphonic acid.

Changes in gastric emptying and orocaecal transit time in patients with ulcerative colitis suggest that disturbances in gut motility may not be restricted to inflamed sites. This study sought to characterize changes in the motility of noninflamed ileum in a rat colitis model and to explore the mechanism(s) potentially involved. The myoelectrical activity of the ileum was recorded in rats with trinitrobenzene sulphonic acid (TNBS)-induced colitis. The degree of ileal and colonic inflammation was assessed by quantification of macroscopic damage and myeloperoxidase activity (MPO). The effect on ileal motility of pretreatment with atropine, indomethacin and NG-nitro-L-arginine-methyl ester (L-NAME) was investigated. TNBS-induced inflammation was restricted to the distal colon, as evidenced by morphological scores and MPO. Colitis was associated with increased frequency of ileal migrating motor complexes, characterized mainly by a decrease in the duration of phases I and III. The occurrence of ileal giant migrating complexes remained unchanged. The myoelectrical changes observed in the ileum persisted after treatment with atropine, indomethacin and L-NAME. Distal colitis is associated with abnormal myoelectrical activity in the noninflamed ileum of rats. Neither acetylcholine nor prostaglandins and nitric oxide seem to be involved.

Proinflammatory role of leptin in experimental colitis in rats benefit of cholecystokinin-B antagonist and beta3-agonist.

Leptin, a hormone primarily secreted from adipocytes, plays a key role in controlling body weight homeostasis. In vitro studies indicate that it is also implicated in immune responses. Hyperleptinaemia has been reported in acute inflammation, especially during the early stages of intestinal inflammation in rats. The present study investigated the possible role of leptin in the pathogenesis of trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. Since no specific antagonist of leptin is available, a CCK-B antagonist (YM022) and a beta3 agonist (BRL37344) were used in this study to inhibit leptin secretion. Colitis was induced by intracolonic instillation of TNBS in rats. Five TNBS-groups were subcutaneously implanted with micropumps containing: placebo, YM022, BRL37344, BRL37344 and exogenous leptin simultaneously, or leptin alone. At sacrifices, colitis severity was assessed by macroscopic and histological scoring systems and by determination of tissue myeloperoxidase activity. The TNBS-induced hyperleptinaemia was significantly reduced by YM022 and BRL37344 (p<0.05). Inhibition of leptin secretion markedly reduced colonic inflammation, whatever the criteria considered (i.e. macroscopic, histological or biochemical). In contrast, administration of exogenous leptin completely abolished the beneficial effect of leptin-lowering drugs on colitis severity. These results provide the first direct evidence for an important deleterious role of leptin in the pathogenesis of experimental intestinal inflammation and suggest that a pro-inflammatory activity is attributable to leptin in vivo. Further studies are required to determine if these results have clinical significance.

Relationships between transit time in man and in vitro fermentation of dietary fiber by fecal bacteria.

OBJECTIVE: To assess the effects of drug-induced changes in mean transit time (MTT) on the activity of human fecal flora in vitro. METHODS: The activity of fecal flora was estimated by the ability of a fecal inoculum to ferment a substrate (beet fiber) in vitro in a batch system for 24 h. The inoculum was collected from 8 healthy volunteers studied during three 3-week randomized periods, who received a controlled diet alone (control period) or the same diet with either cisapride or loperamide. Cisapride and loperamide were adjusted in order to halve and double MTT measured during the control period. At the end of each period, the percentage disappearance of the initial added substrate and the concentration and the profile of short-chain fatty acids (SCFAs), were determined. RESULTS: In the control period, the pH of the inoculum and SCFA concentration were inversely related to MTT (P=0.0001). Individual SCFA production was also significantly related to MTT (P<0.01). Cisapride-reduced transit time was associated with a significant rise in the concentrations of total SCFAs (P<0.05), propionic and butyric acids (P<0.05) and the percentage substrate disappearance (P<0.05). Inverse relations were observed during the loperamide period. Moreover, MTT was inversely related to the percentage substrate disappearance (P<0.001), SCFA production (P<0.001) and butyrate production (P<0.0005). CONCLUSION: Changes in MTT alter bacterial activity and modify the bacterial pathways affecting the proportion of individual SCFAs. European Journal of Clinical Nutrition (2000) 54, 603-609

Does the route of feeding modify gastric emptying in rats?

BACKGROUND: It has been shown that the pattern of previous nutrient intake can influence gastric emptying. However, the effect of the absence of enteral stimulation in the setting of a normal energy supply on gastric emptying has not been examined. The aim of this study was to determine whether the absence of enteral stimulation during total parenteral nutrition (TPN) could modify gastric emptying in rats. METHODS: Two experiments were performed. First, gastric emptying of a peptone meal was compared between rats receiving TPN, oral liquid diet (same solution as TPN), or regular diet (control group) for 10 days. In the second experiment, gastric emptying of two test meals (40% peptone and 25% glucose) was studied before and after rats received TPN or intragastric nutrition (same solution as TPN) for 10 to 12 days. RESULTS: In experiment 1, gastric emptying of 40% peptone in the TPN and liquid diet groups was slower than that in the control group. This difference was significant between the TPN group and the control group (p < .01) but not between the liquid diet and control groups (p = .076). Gastric emptying of this meal in the TPN and liquid diet groups was similar. In experiment 2, no difference in gastric emptying of 40% peptone or 25% glucose was found between rats receiving TPN and those receiving intragastric nutrition for 10 to 12 days. CONCLUSIONS: The composition of diet not the route of feeding is important in the modification of gastric emptying by the pattern of previous nutrient intake.

Relationships between electromyographic ileal and colonic motility patterns in cats during fasting and feeding.

The relationship between ileal and colonic electromyographic motility patterns were investigated in six awake cats chronically fitted with subserosal electrodes implanted in the smooth muscles of the ileum and colon. Smooth muscle electrical activity (electromyogram) was recorded in both fed and fasted conditions under a 12-12 hours dark-light schedule. It consisted of electrical long spike bursts having two different patterns for each condition. Short sequences of three to five long spike bursts were propagated either aborally or orally from any part of the colon; they were most frequent during the interdigestive or fasting period and no relationship was observed between these long spike bursts and the electrical activity of the ileum. During the digestive or feeding period, the colonic activity was organized in long sequences of 10-15 long spike bursts, termed migrating spike bursts, which started near the caecal junction and propagated aborally to the distal colon. These migrating spike bursts were correlated with the ileal motility. This relationship demonstrated between ileum and colon after feeding is dependent upon the amount of food intake.

[Changes in electromyogram of the colon related to ingestion of undigestible particles in dogs]. / Modifications de l'électromyogramme du côlon liées à l'ingestion de particules non digestibles chez le chien.

The relationship between undigestible particle intake and myoelectric activity of the colon was examined in three dogs fed with a low-fiber diet alone or with polyethylene particles containing 10 p. 100 and 45 p. 100 of dry matter. When compared to controls colonic electromyograms of dogs fed on polyethylene revealed a 40 p. 100 reduction in long spike bursts (LSBs). The sequences of LSBs propagated over long distances, or MSBs (migrating spike bursts) were unchanged and only the myoelectric activity corresponding to LSBs propagated for very short distances was abolished by polyethylene diets. Concurrently, the percentage of water excreted in the feces was increased. Undigestible and inert particles were thus able to modify the colonic motor profile and to increase the fecal excretion of water. Such effects were similar to those observed with dietary fibers. It is suggested that dietary fiber effects on fecal excretion and colonic motility are partially induced by their mechanical action on the intestinal wall. In addition, the absence of LSBs propagated in both directions and for short distances on the canine proximal and transverse colons seems to be a limiting factor in the movements of water absorption.

Vasoactive intestinal peptide is involved in the inhibitory effect of interleukin-1 beta on the jejunal contractile response induced by acetylcholine.

UNLABELLED: Although previous studies have shown that interleukin-1 beta (IL-1 beta) decreases acetylcholine (ACh)-induced intestinal contraction by an action on the enteric nervous system, the neuromediator(s) involved are still unknown. AIM: To determine the role of nitric oxide (NO), vasoactive intestinal peptide (VIP) and/or adenosine triphosphate (ATP) in mediating this inhibitory effect. METHODS: The effects of NO synthase inhibitors, VIP and ATP antagonists on motor response to the ACh were investigated before and after 90-min exposure of a rat preparation of jejunal longitudinal muscle-myenteric plexus to IL-1 beta. NG-nitro-L-arginine methyl ester, NG-nitro-L-arginine and NG-monomethyl-L-arginine were used to inhibit NO synthase, VIP (10-28) and [D-p-Cl-Phe6, Leu17] VIP to block VIP receptors, and suramin to block ATP receptors. RESULTS: NO synthase inhibitors failed to block the inhibitory effect of IL-1 beta on ACh-contracted jejunum smooth muscle. Suramin also failed to affect IL-1 beta-induced inhibition, whereas VIP antagonists abolished it. Moreover, the action of IL-1 beta was partly reproduced by VIP. CONCLUSIONS: While neither NO nor ATP accounts for the inhibitory effect of IL-1 beta on ACh-contracted jejunum, VIP seems to be a key-mediator of this effect.

[Are intraluminal electrodes reliable for recording myoelectric activity of the small intestine?]. / Les électrodes annulaires endoluminales sont-elles fiables pour le recueil de l'activité myoélectrique de l'intestin grêle?

In humans except for the postoperative state, electromyographic activity of the small bowel can only be recorded with intraluminal electrodes. The aim of this study was to validate the use of intraluminal electrodes in pigs by comparing the signal recorded from such electrodes to those recorded with surgically implanted electrodes. A polyethylene probe equipped with bipolar ring-shaped electrodes was placed in the lumen of the proximal jejunum of 6 pigs, at the same level as intramuscular implanted electrodes. The signals were recorded in conscious pigs fed normally. By comparison to the myoelectric activity recorded from the intramuscular implanted electrodes, the intraluminal electrodes provided reliable spike burst detection (sensitivity 85 p. 100; positive predictive value 91 p. 100) in the fasted and fed state, and good identification of migrating myoelectric complexes. Spectral analysis showed the same frequency patterns for signals obtained with both types of electrodes. In conclusion, intraluminal ring-shaped electrodes allow reliable detection of small bowel myoelectric activity and may represent a useful tool for motility studies in man.

[Digital storage and semi-automatic analysis of esophageal pressure signals. Evaluation of a commercialized system (PC Polygraft, Synectics)]. / Numérisation directe et traitement semi-automatique des signaux de pressions oesophagiens. Evaluation d'un système commercialisé (PC Polygraf, Synectics).

The aim of this work was to evaluate a new commercially available pressure recording system (PC Polygraf, Synectics) and to compare this system with a classical method using perfused catheters. The PC Polygraf uses microtransducers and allows direct digitized storage and semi-automatic analysis of data. In the first part of this study, manometric assessment was conducted using only perfused catheters. The transducers were connected to both an analog recorder and to a PC Polygraf. Using the two methods of analysis, contraction amplitudes were strongly correlated (r = 0.99; p less than 0.0001) whereas durations were significantly but loosely correlated (r = 0.51; p less than 0.001). Resting LES pressure was significantly correlated (r = 0.87; p less than 0.05). In the second part of this study, simultaneous recordings of esophageal pressure were conducted in 7 patients, by placing side by side the two tubes (microtransducers and perfused catheters) with the sideholes at the same level. The characteristics of the waves were determined both by visual analysis of analog tracing and by semi-automatic analysis of digitized recording with adequate program. Mean amplitude was lower with the microtransducers than with the perfused catheters (60 vs 68 cm H2O; p less than 0.05), but the duration of waves was not significantly different when using both systems. Values obtained for each of these parameters using both methods were significantly correlated (amplitude: r = 0.74; duration: r = 0.51). The localization and the measure of the basal tone of sphincter were found to be difficult when using microtransducers. These results show that PC Polygraf allows a satisfactory analysis of esophageal pressure signals. However, only perfused catheters offer an excellent reliability for complete studies of both sphincter and peristaltism.

Effects of short-chain fatty acids on gastrointestinal motility.

Besides their action on gut morphology and function, short-chain fatty acids (SCFAs), produced by bacterial fermentation of carbohydrates in the colon, influence gastrointestinal motility. As they are not present in the stomach and proximal small intestine, SCFAs do not directly affect motility of these segments. However, caecal infusion of SCFAs as well as colonic fermentation of lactulose induce a relaxation of the proximal stomach in humans, indicating that SCFAs can affect motility at a distance from their site of production. Moreover, this suggests that SCFAs may be involved in the so-called "ileocolonic brake', i.e. the inhibition of gastric emptying by nutrients reaching the ileo-colonic junction. In the terminal ileum, where their concentration may increase following a colo-ileal reflux, SCFAs stimulate contractions and shorten ileal emptying, which may protect ileal mucosa against the potentially harmful effects of the reflux of colonic contents. Although SCFAs are produced and concentrated in the colon, their action on motility of this organ is not clearly understood and may depend on concentration, molecular structure of the acids, responsiveness of the colonic segments and animal species. The mechanisms of action of SCFAs on gastrointestinal motility are not completely elucidated. They may involve systemic humoral and neural pathways as well as local reflexes and myogenic responses.

MUC genes are differently expressed during onset and maintenance of inflammation in dextran sodium sulfate-treated mice.

Colonic mucosal protection is provided by mucous gel, mainly composed of secreted (Muc2) and membrane-bound (Muc1, Muc3, Muc4) mucins. Our aim was to determine the expression profile of secreted and membrane-bound mucins in experimental dextran sulfate sodium (DSS)-induced colitis. Acute colitis was induced in Balb/C mice by oral administration of 1.0% DSS (5 days) and chronic colitis was maintained by subsequent 0.15% DSS treatment (28 days). Clinical symptoms (mortality, weight gain), stool scores, and MPO activity confirmed the inflammatory state in the two phases of colitis. Muc2 gene expression was not modified by colitis, whereas Muc3 gene expression was increased (x2) only in the cecum and the distal colon of mice after acute colitis. Muc1 and Muc4 mRNA levels were more significantly increased in the cecum (x8-10) than in colonic segments (x4) after acute colitis. TFF3 involved in mucosal repair was up-regulated during colitis induction. These results indicate that Muc and TFF3 genes are regulated early in inflammation and suggest that their mRNA levels could be used as early markers of inflammation.

Lactate is mainly fermented to butyrate by human intestinal microfloras but inter-individual variation is evident.

AIM: To assess the role of lactate as a precursor for butyrate biosynthesis in human colonic microflora. METHODS AND RESULTS: Three human faecal microfloras were incubated in vitro with media supplemented with 30 mmol l(-1) unenriched or 13C-enriched lactate. Lactate metabolism and short-chain fatty acid (SCFA) production were quantified. Lactate conversion to butyrate was investigated by gas chromatography-mass spectrometry and the pathways involved were identified by 13C nuclear magnetic resonance spectroscopy. All human faecal microfloras rapidly and completely fermented lactate, yielding approx. 19 mmol l(-1) total SCFAs. However, the SCFA composition varied markedly between microfloras. Butyrate was the main end-product for two microfloras but not for the third (60 and 61%vs 27% of the net concentration of SCFA produced respectively). The latter was typified by its ability to produce propionate as a major product (37%), and valerate (3%). 13C-Labelling showed that butyrate was produced through the acetyl-CoA pathway and that the three microfloras possessed significant differences in their metabolic pathways for lactate consumption. CONCLUSIONS: In contrast to the ruminal microflora, the human intestinal microflora can utilize both d- and l-lactate as precursors for butyrate synthesis. Inter-individual variation is found. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that the butyrogenic capability of colonic prebiotics could be related to lactate availability. These findings will direct the development of selection strategies for the isolation of new butyrate-producing bacteria among the lactate-utilizing bacteria present in the human intestinal microfloras.

Inulin and oligofructose in the dietary fibre concept.

Dietary fibre consists of remnants of edible plant cell polysaccharides and associated substances resistant to hydrolysis by human alimentary enzymes, which may benefit health through a wide range of physiological effects. Inulin and oligofructose are storage carbohydrates found in a number of vegetables, fruits and whole grains. They resist digestion and absorption in the stomach and small intestine of humans, as shown by their almost full recovery at the end of the ileum of healthy or ileostomised volunteers. Inulin and oligofructose thus enter into the large intestine where they are available to fermentation, as demonstrated by increased breath hydrogen. Fermentation of both substrates is complete and no residue is found in human stools. Inulin and oligofructose improve laxation. Their bulking capacity comprised between 1.2 and 2.1 g of stool per g of ingested substrate, results mainly from increases in microbial biomass in the colon. As water content of bacterial cells is high, stools are softer and easier to expulse. Stool frequency is thus increased, particularly in slightly constipated individuals. In addition, likely due to their fermentation properties, inulin and oligofructose also affect the intestinal epithelium (trophicity, mucin expression, etc.), that may strengthen mucosal protection and reduce the risk of gastrointestinal diseases. In summary, inulin and oligofructose are plant carbohydrates, resistant to digestion in the human small intestine and fermented by colonic bacteria. They exert several intestinal physiological effects contributing to maintenance of health. Therefore, inulin and oligofructose fit well within the current concept of dietary fibre.

The effect of indigestible particles on digestive transit time and colonic motility in dogs and pigs.

The myoelectric activity of the colon was examined in three dogs and three pigs when they were given a basal diet or a basal diet plus indigestible particles (IP), 2 mm in diameter, at 100 g/kg dry matter. The mean retention time was determined using coloured discs as a marker added to the daily meal. Colonic electromyograms of dogs and pigs given IP revealed a 30% reduction in the number of long spike bursts (LSB) when compared with controls. The other components, propulsive migrating spike bursts (MSB) or non-propulsive short spike bursts (SSB), were unchanged. Mean retention time was decreased from 28.6 h to 17.6 h in dogs and from 129 h to 94.2 h in pigs. These changes developed progressively during 3-4 d in both species, suggesting that the reduction in motor activity was an adaptation to the changes in bulk contents. From the decreased motility of the colon linked to the reduction of LSB and paralleled by an increased transit time, it was concluded that one of the functions of the LSB is to impede the passage of digesta.

Effect of diet on intestinal xylose absorption in dogs.

The absorption of xylose at different levels of the intestine was compared in five dogs receiving diets containing either wheat bran, polyethylene particles (PE), or horse-bean hulls. The absorption was determined by serial collection of the interstitial fluid (ISF) in different parts of the small intestine and colon, and blood concentration after the administration of D-xylose as a solution (0.5 g/kg body weight) into the duodenal bulb. Xylose was mostly absorbed from the duodenum, and its concentration in the duodenal ISF and in plasma was reduced on a diet containing fiber, irrespective of the nature of fiber. In contrast, a negative linear relation between the mean retention time of digesta in the small intestine and the amount of xylose absorbed by duodenum was evidenced (r = -0.843). The results indicate that changes in transit linked to the presence of fiber in a diet are a major operative factor in the rate of carbohydrate absorption. They suggest that the absorption can be affected by a relatively minor change in the intestinal transit of digesta.

Influence of particle size and sources of non-starch polysaccharides on postprandial glycaemia, insulinaemia and triacylglycerolaemia in pigs and starch digestion in vitro.

Physico-chemical properties of dietary fibres might be involved in metabolic control, particularly of the postprandial blood glucose response. The aim of the present study was to look at the effects of the content of soluble fibres and of the particle size of solid fibres on in vitro and in vivo starch hydrolysis and on the subsequent glucose absorption as well as the triacylglycerolaemia. Two sources of dietary fibres, one, with soluble fibres (beet pulp), the other with mostly insoluble fibres (wheat bran), were added at the rate of 60 g/kg to a meal simulating human food. The fibre sources were ground in order to obtain two different particle sizes (250 and 500 microns). Beet pulp decreased significantly (P < 0.05) initial in vitro hydrolysis whereas wheat bran increased starch hydrolysis in the first 10 min. Wheat bran and beet pulp, whatever its particle size, lowered the post-prandial triacylglycerol response. No significant effect was found with dietary fibre-supplemented diets on postprandial glycaemic and insulinaemic values. High correlation was found between initial in vitro starch hydrolysis and mean areas under the insulinaemic curves. This in vitro model can be used to predict initial in vivo digestion of carbohydrates from complex foods.