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.

Butyrate specifically modulates MUC gene expression in intestinal epithelial goblet cells deprived of glucose.

The mucus layer covering the gastrointestinal mucosa is considered the first line of defense against aggressions arising from the luminal content. It is mainly composed of high molecular weight glycoproteins called mucins. Butyrate, a short-chain fatty acid produced during carbohydrate fermentation, has been shown to increase mucin secretion. The aim of this study was to test 1) whether butyrate regulates the expression of various MUC genes, which are coding for protein backbones of mucins, and 2) whether this effect depends on butyrate status as the major energy source of colonocytes. Butyrate was provided at the apical side of human polarized colonic goblet cell line HT29-Cl.16E in glucose-rich or glucose-deprived medium. In glucose-rich medium, butyrate significantly increased MUC3 and MUC5B expression (1.6-fold basal level for both genes), tended to decrease MUC5AC expression, and had no effect on MUC2 expression. In glucose-deprived medium, i.e., when butyrate was the only energy source available, MUC3 and MUC5B increase persisted, whereas MUC5AC expression was significantly enhanced (3.7-fold basal level) and MUC2 expression was strikingly increased (23-fold basal level). Together, our findings show that butyrate is able to upregulate colonic mucins at the transcriptional level and even better when it is the major energy source of the cells. Thus the metabolism of butyrate in colonocytes is closely linked to some of its gene-regulating effects. The distinct effects of butyrate according to the different MUC genes could influence the composition and properties of the mucus gel and thus its protective function.

Raw potato starch and short-chain fructo-oligosaccharides affect the composition and metabolic activity of rat intestinal microbiota differently depending on the caecocolonic segment involved.

AIMS: In vitro studies have suggested that fructo-oligosaccharides (FOS) and resistant starch (two fermentable non-digestible carbohydrates) display different fermentation kinetics. This study investigated whether these substrates affect the metabolic activity and bacterial composition of the intestinal microflora differently depending on the caecocolonic segment involved. METHODS AND RESULTS: Eighteen rats were fed a low-fibre diet (Basal) or the same diet containing raw potato starch (RPS) (9%) or short-chain FOS (9%) for 14 days. Changes in wet-content weights, bacterial populations and metabolites were investigated in the caecum, proximal and distal colon and faeces. Both substrates exerted a prebiotic effect compared with the Basal diet. However, FOS increased lactic acid-producing bacteria (LAPB) throughout the caecocolon and in faeces, whereas the effect of RPS was limited to the caecum and proximal colon. As compared with RPS, FOS doubled the pool of caecal fermentation products, while the situation was just the opposite distally. This difference was mainly because of the anatomical distribution of lactate, which accumulated in the caecum with FOS and in the distal colon with RPS. Faeces reflected these impacts only partly, showing the prebiotic effect of FOS and the metabolite increase induced by RPS. CONCLUSIONS: This study demonstrates that FOS and RPS exert complementary caecocolonic effects. SIGNIFICANCE AND IMPACT OF THE STUDY: The RPS and FOS combined ingestion could be beneficial by providing health-promoting effects throughout the caecocolon.

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.

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.

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.

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.

Short-chain fatty acids induce cytoskeletal and extracellular protein modifications associated with modulation of proliferation on primary culture of rat intestinal smooth muscle cells.

Short-chain fatty acids are the main end products of bacterial fermentation of carbohydrates. Their role on the metabolism and biology of colonocytes is now well characterized. However, the functional consequences of their presence on intestinal smooth muscle cells remain poorly studied. We aimed to assess the effect of different short-chain fatty acids on ileal and colonic smooth muscle cells in primary culture and on A7R5 line. Butyrate (above 0.1 mM) inhibited A7R5 cell proliferation, while at low concentration (0.05 to 0.5 mM) butyrate significantly stimulated the proliferation of ileal and colonic myocytes in primary culture. An inhibition was observed at higher concentrations. Collagenous and noncollagenous protein synthesis was stimulated by butyrate. Moreover, butyrate stimulated actin and myosin expression. Thus, butyrate, which is produced by dietary fiber fermentation, may affect intestinal muscles by directly acting at the molecular level on myocytes.

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.

Modulation by colonic fermentation of LES function in humans.

Colonic fermentation of carbohydrate has been shown to influence gastric and intestinal motility. Our aim was to investigate the effects of colonic infusion of lactose and short-chain fatty acids (SCFAs) on lower esophageal sphincter (LES) function in humans. LES pressure (LESP), transient relaxations of LES (TLESRs), and esophageal pH were monitored over 6 h on 4 different days in 7 healthy volunteers. After 1 h of baseline recording, the effects of different colonic infusions (270 ml of isotonic or hypertonic saline, 30 g lactose, or 135 mmol SCFAs) were tested in fasting conditions and after a standard meal. Peptide YY (PYY) and oxyntomodulin (OLI) were also measured in plasma. Both lactose and SCFA infusions increased the number of TLESRs as well as the proportion of TLESRs associated with acid reflux episodes, but saline solutions did not. The postprandial fall of LESP was enhanced by previous SCFA infusion. Plasma PYY and OLI increased similarly after all colonic infusions. Colonic fermentation of lactose markedly affected LES function, and this effect was reproduced by SCFA infusion. Whether the mechanisms of this feedback phenomenon are of hormonal nature, neural nature, or both remains to be determined.

Butyrate and trichostatin A effects on the proliferation/differentiation of human intestinal epithelial cells: induction of cyclin D3 and p21 expression.

BACKGROUND: Sodium butyrate, a product of colonic bacterial fermentation, is able to inhibit cell proliferation and to stimulate cell differentiation of colonic epithelial cell lines. It has been proposed that these cellular effects could be linked to its ability to cause hyperacetylation of histone through the inhibition of histone deacetylase. AIM: To analyse the molecular mechanisms of butyrate action on cell proliferation/differentiation and to compare them with those of trichostatin A, a well known inhibitor of histone deacetylase. METHODS: HT-29 cells were grown in the absence or presence of butyrate or trichostatin A. Cell proliferation and cell cycle distribution were studied after DNA staining by crystal violet and propidium iodide respectively. Cell cycle regulatory proteins were studied by western blot and reverse transcription-polymerase chain reaction. Cell differentiation was followed by measuring brush border enzyme activities. Histone acetylation was studied by acid/urea/Triton acrylamide gel electrophoresis. RESULTS: Butyrate blocked cells mainly in the G(1) phase of the cell cycle, whereas trichostatin A was inhibitory in both G(1) and G(2) phases. Butyrate inhibited the mRNA expression of cyclin D1 without affecting its protein expression and stimulated the protein expression of cyclin D3 without affecting its mRNA expression. Trichostatin A showed similar effects on cyclin D1 and D3. Butyrate and trichostatin A stimulated p21 expression both at the mRNA and protein levels, whereas their effects on the expression of cyclin dependent kinases were slightly different. Moreover, butyrate strongly stimulated the activity of alkaline phosphatase and dipeptidyl peptidase IV, whereas trichostatin A had no effect. Finally, a six hour exposure to butyrate or trichostatin A induced histone H4 hyperacetylation. At 15 and 24 hours, histone H4 remained hyperacetylated in the presence of butyrate, whereas it returned to control levels in the presence of trichostatin A. CONCLUSIONS: The data may explain how butyrate acts on cell proliferation/differentiation, and they show that trichostatin A does not reproduce every effect of butyrate, mainly because of its shorter half life.

Pathways and receptors involved in peptide YY induced contraction of rat proximal colonic muscle in vitro.

BACKGROUND: Peptide YY (PYY) is involved in the regulation of several gut functions, including secretion and motility. It exerts its effects through a family of six receptors, commonly named the Y receptor family. AIMS: To characterise the effects of PYY on strips of rat proximal colon in vitro, and to determine the pathways and receptors involved. METHODS: Contractions of strips removed from the muscle layer of rat proximal colon were recorded under isometric conditions, using PYY, Y receptor agonists and antagonists, and nerve blockers. Reverse transcription-polymerase chain reaction was also performed to detect the presence of mRNA coding for Y receptors. Finally, smooth muscle cells were isolated to estimate the cell length and intracellular Ca(2+) concentration in the presence and absence of PYY. RESULTS: PYY, neuropeptide Y (NPY), pancreatic polypeptide (PP) and [Leu31,Pro34]NPY induced a dose dependent contraction of strips from proximal colon. Tetrodotoxin partially inhibited the PYY and NPY induced contractions, and strongly inhibited the PP induced contraction. Specific antagonists showed the involvement of cholinergic nicotinic receptors and NK1 receptor. BIBP 3226, a specific Y1 antagonist, did not modify the colonic smooth muscle response to PYY, whereas blocking L-type Ca(2+) channels with D-600 abolished its effects. Moreover, PYY induced an increase in intracellular Ca(2+) concentration, associated with a reduction in cell length. mRNA encoding Y1 and Y4 receptors were detected in the muscle strips. CONCLUSIONS: These findings suggest that PYY stimulates colonic contractile activity in vitro through (a) a nervous Y4 dependent pathway and (b) a pathway involving a potential new receptor on myocytes.

Prolonged intake of fructo-oligosaccharides induces a short-term elevation of lactic acid-producing bacteria and a persistent increase in cecal butyrate in rats.

While the prebiotic effects of fructo-oligosaccharides (FOS), short-chain polymers of fructose, have been thoroughly described after 2-3 wk of ingestion, effects after intake for several months are unknown. We tested the hypothesis that these effects would differ after ingestion for short and long periods in rats. Rats were fed a basal low-fiber diet (Basal) or the same diet containing 9 g/100 g of FOS for 2, 8 or 27 wk, and cecal contents were collected at the end of each time period. Cecal short-chain fatty acid concentration was higher in rats fed FOS than in those fed Basal, and this effect persisted over time: 83.8 +/- 4.1 vs. 62.4 +/- 6.5 micromol/g at 2 wk and 103.5 +/- 5.8 vs. 73.2 +/- 7.4 micromol/g at 27 wk (P < 0.05). The molar butyrate ratio was higher in rats fed FOS regardless of the time period (14.8 +/- 0.6% vs. 6.7 +/- 1.1% at 27 wk, P < 0.05). Lactate concentration in rats fed FOS was elevated after 2 wk and then decreased: 63.5 +/- 21.6 micromol/g at 2 wk vs. 8.8 +/- 3.3 micromol/g at 8 wk (P < 0.05). After 2 wk, FOS increased the concentrations of total lactic acid-producing bacteria, and Lactobacillus sp. (P < 0.05), without modifying total anaerobes. However, most of these effects were abolished after 8 and 27 wk of FOS consumption. In the long term, the FOS-induced increase in intestinal lactic acid-producing bacteria was lost, but the butyrogenic properties of FOS were maintained.

Biological properties of ulvan, a new source of green seaweed sulfated polysaccharides, on cultured normal and cancerous colonic epithelial cells.

Ulvans (from Ulva lactuca) constitute a dietary fiber structurally similar to the mammalian glycosaminoglycans but with unexplored biological or cytotoxic activities. From native low-viscosity preparations containing 33.5 molar % and 18.4 molar % of sulfate residues and uronic acid residues, respectively, we derived desulfated, reduced and desulfated-reduced polysaccharides with respectively 5.2, 2.9, and 4.5-4.9 molar % of sulfate residues and uronic acid residues. The effects of these preparations were examined on the adhesion, proliferation and differentiation of normal or tumoral colonic epithelial cells cultured in conventional (0.3-0.8 x 10(6) cells/ml) or rotating bioreactor (3-8 x 10(6) cells/ml) culture conditions. In conventional culture conditions, ulvan modified the adhesion phase and the proliferation of normal colonic cells and undifferentiated HT-29 cells according to their molecular weights and to the relative molar proportion of sulfate residues. From the native polysaccharides, we have screened sulfated ulvans (MW < 5,000) which inhibited the Caco-2 cell proliferation/differentiation program by inducing a low cell reactivity to Ulex europeaus-1 lectins in defined (p < 0.001) or serum-supplemented media (p < 0.01) but were inactive on normal colonocytes. In conclusion, this dietary fiber could be a source of oligosaccharides with a bioactivity, a cytotoxicity or a cytostaticity targeted to normal or cancerous epithelial cells.

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.

Enhancement of butyrate production in the rat caecocolonic tract by long-term ingestion of resistant potato starch.

Some data suggest that the colonic microflora may adapt to produce more butyrate if given time and the proper substrate. To test this hypothesis, we investigated the effect of prolonged feeding of resistant potato starch on butyrate production. Rats were fed on either a low-fibre diet (basal) or the same diet supplemented with 90 g resistant potato starch/kg (PoS) for 0.5, 2 and 6 months. Short-chain fatty acid (SCFA) concentrations were determined in caecal and colonic contents at the end of each ingestion period. Total SCFA concentration increased over time throughout the caecocolonic tract with PoS, but was not modified with the basal diet. While propionate concentration was unchanged, butyrate concentration was highly increased by PoS at each time period in both the caecum and colon. Moreover, the butyrogenic effect of PoS increased over time, and the amount of butyrate was increased 6-fold in the caecum and proximal colon and 3-fold in the distal colon after 6 months compared with 0.5 months. Accordingly, the ratio butyrate:- total SCFA increased over time throughout the caecocolonic tract (12.6 (SE 2.8) v. 28 (SE 1.8)% in the caecum, 10.5 (SE 1.4) v. 26.8 (SE 0.9)% in the proximal colon, and 7.3 (SE 2.4) v. 23.9 (SE 2.7)% in the distal colon at 0.5 v. 6 months respectively), while the proportion of acetate decreased. Neither the proportion nor the concentration of butyrate was modified over time with the basal diet. Butyrate production was thus promoted by long-term ingestion of PoS, from the caecum towards the distal colon, which suggests that a slow adaptive process occurs within the digestive tract in response to a chronic load of indigestible carbohydrates.

Short-chain fatty acids modify colonic motility through nerves and polypeptide YY release in the rat.

Short-chain fatty acids (SCFAs) are recognized as the major anions of the large intestinal content in humans, but their effect on colonic motility is controversial. This study explores the colonic motor effect of SCFAs and their mechanisms in the rat. Colonic motility (electromyography) and transit time (plastic markers) were measured in conscious rats while SCFAs were infused into the colon, either alone or after administration of neural antagonists or immunoneutralization of circulating polypeptide YY (PYY). SCFA-induced PYY release was measured by RIA and then simulated by infusing exogenous PYY. Intracolonic infusion of 0.4 mmol/h SCFAs had no effect, whereas 2 mmol/h SCFAs reduced colonic motility (36 +/- 3 vs. 57 +/- 4 spike bursts/h with saline, P < 0.05) by decreasing the ratio of nonpropulsive to propulsive activity. This resulted in an increased transit rate (P < 0.01). Neither alpha-adrenoceptor blockade nor nitric oxide synthase inhibition prevented SCFA-induced motility reduction. Intraluminal procaine infusion suppressed the SCFA effect, indicating that a local neural mechanism was involved. SCFA colonic infusion stimulated PYY release in blood. Immunoneutralization of circulating PYY abolished the effect of SCFAs on colonic motility, whereas exogenous PYY infusion partly reproduced this effect. SCFAs modify colonic motor patterns in the rat and increase transit rate; local nerve fibers and PYY are involved in this effect.

Elevated plasma leptin concentrations in early stages of experimental intestinal inflammation in rats.

BACKGROUND: Although leptin, an adipocyte derived hormone which regulates food intake and energy balance, is released after injections of tumour necrosis factor (TNF) and interleukin 1, plasma concentrations have not been characterised in chronic inflammation. Leptin may contribute to the anorexia and body weight loss associated particularly with the acute stages of inflammatory bowel disease. AIMS: To investigate plasma leptin concentrations during the time course of intestinal inflammation in different animal models. METHODS: Plasma leptin was measured at different time points in rats with trinitrobenzene sulphonic acid (TNBS) induced colitis, indomethacin induced ileitis, or endotoxic shock caused by lipopolysaccharide (LPS). Systemic TNF-alpha was also measured during acute inflammation. RESULTS: Plasma leptin concentrations increased fourfold eight hours after induction of TNBS colitis (p<0.0001) and twofold after administration of ethanol alone (p<0.02). Plasma leptin responses throughout the first post-treatment day were correlated with myeloperoxidase activity and gross damage scores. Similar leptin overexpression was observed in indomethacin induced ileitis and in rats with endotoxic shock. Plasma concentrations were lower in TNBS treated rats than in controls on day 5 before reaching a similar concentration on day 14. Anorexia and body weight loss were observed during the first four days post-TNBS. A significant increase in systemic TNF-alpha was only detected in LPS treated rats. CONCLUSION: Elevated plasma leptin concentrations, correlated with the degree of inflammation and associated with anorexia, were induced in rats during the early stages of experimental intestinal inflammation but proved transient; this might account for discrepancies in recent results concerning concentrations in patients with inflammatory bowel diseases.