Caecum Of Rats Research Articles

Hydrolysis and Fermentation by Rat Gut Microorganisms of 2-O-β-D-Xylopyranosyl (5-O-Feruloyl)-L-Arabinose Derived from Grass Cell Wall Arabinoxylan

It has been shown that a common side-chain of grass cell wall arabinoxylans is 2-O-β-D-xylopyranosyl-(5-O-feruloyl)-L-arabinose [X(F)A]. The stability of X(F)A was determined by incubation of (feruloyl-U-14C)-labelled X(F)A and (pentosyl-1-3H)-labelled X(F)A anaerobically with rat caecal contents and chromatographic analysis of the radioactive products. The ester linkage was hydrolysed very rapidly to form ferulic acid (which was stable) and the disaccharide (XA). The 3H-XA was further metabolised, but 3H-monosaccharides did not accumulate. In the end-products of fermentation of (pentosyl-3H)-labelled X(F)A, 67% of the 3H was present in bacterial polymers. In contrast, when free [1-3H]arabinose was incubated with rat caecal contents, 74% of the 3H quickly became volatile, probably as 3H2O. It is concluded that X(F)A is highly susceptible to (feruloyl)esterase activity produced by bacteria present in the rat caecum, and that the disaccharide produced is further fermented, but not via the production of extracellular arabinose and xylose. © 1997 SCI.

Hydrolysis and Fermentation by Rat Gut Microorganisms of 2-O-β-D-Xylopyranosyl (5-O-Feruloyl)-L-Arabinose Derived from Grass Cell Wall Arabinoxylan

It has been shown that a common side-chain of grass cell wall arabinoxylans is 2-O-β-D-xylopyranosyl-(5-O-feruloyl)-L-arabinose [X(F)A]. The stability of X(F)A was determined by incubation of (feruloyl-U-14C)-labelled X(F)A and (pentosyl-1-3H)-labelled X(F)A anaerobically with rat caecal contents and chromatographic analysis of the radioactive products. The ester linkage was hydrolysed very rapidly to form ferulic acid (which was stable) and the disaccharide (XA). The 3H-XA was further metabolised, but 3H-monosaccharides did not accumulate. In the end-products of fermentation of (pentosyl-3H)-labelled X(F)A, 67% of the 3H was present in bacterial polymers. In contrast, when free [1-3H]arabinose was incubated with rat caecal contents, 74% of the 3H quickly became volatile, probably as 3H2O. It is concluded that X(F)A is highly susceptible to (feruloyl)esterase activity produced by bacteria present in the rat caecum, and that the disaccharide produced is further fermented, but not via the production of extracellular arabinose and xylose. © 1997 SCI.

Apamin‐sensitive and ‐insensitive components of inhibitory junction potentials in rat caecum: role of nitric oxide

1. The non-adrenergic non-cholinergic (NANC) inhibitory response to electrical field stimulation (EFS) in circular muscle from rat caecum was investigated using the single sucrose-gap technique. EFS with single pulses evoked hyperpolarization oral inhibitory function potential (IJP) of the membrane associated with muscular relaxation or with transient inhibition of spontaneous contractile activity. 2. The amplitude and the duration of the IJPs were enhanced by using train stimulation at increasing frequency. 3. Apamin (10(-7) M) reduced the amplitude of IJPs at all frequencies tested. 4. N omega-nitro-L-arginine methyl ester (L-NAME) (10(-4) M, 5 x 10(-4) M), but not D-NAME, caused a concentration dependent decrease in the amplitude of IJPs at all frequencies tested. L-Arginine (10(-3) M) prevented these effects. 5. L-NAME (5 x 10(-4) M) caused the disappearance of the apamin-resistant IJP-component, evoked by single pulse or by low frequency trains. 6. Sodium nitroprusside (SNP) (10(-4) M), a nitric oxide (NO) donor, induced hyperpolarization of membrane potential and muscular relaxation. SNP-induced effects were not affected by pretreatment of the muscle strips with effective concentrations of tetrodotoxin, apamin, and L-NAME. 7. P2-purinergic antagonists, reactive blue 2 (up to 5 x 10(-4) M) and suramin (up to 3 x 10(-4) M), failed to affect the evoked IJPs. 8. These results show that, in rat caecum, the NANC response to electrical stimulation is composed of two distinguishable components: an apamin-resistant and an apamin-sensitive component. NO or a related compound is mainly involved in the mediation of the apamin-resistant component, while ATP is not the mediator responsible for the apamin-sensitive component.

Acidic fermentation in the caecum increases absorption of calcium and magnesium in the large intestine of the rat

AbstractThe effect of fermentation on colonic absorption of Ca and Mg was investigated in 8-week-old rats adapted to diets containing either digestible wheat starch (DS diets) or including resistant starch, i.e. 350 g raw potato starch/kg (RS diets). The dietary Ca level of the DS and RS diets was 2·5 or 7·5 g/kg. RS diets resulted in enlargements of the caecum together with hypertrophy of the caecal wall. Acidification of the caecal contents by mictobial fermentation of RS was influenced by the dietary Ca level. Very acidic pH conditions and relatively low concentrations of short-chain fatty acids, in the presence of lactic acid fermentation, were observed with the 2·5 g Ca/kg level. Rats fed on RS diets had a bhigher pencentage of soluble Ca (and inorganic phosphate) in the caecum, particularly of rats adapted to the high Ca level. As a result of the hypertrophy of the caecal wall and of an elevated concentration of soluble Cas, the caecal absorption of Ca was 5-6 fold higher in the RS groups than in the DS groups. The difference between dietary intakle and faecal excretion (DI-FE) of Ca was higher in rats fed on RS diets than in those fed on DS diets, when the dietary Ca level was 2·5 g/kg. With the higher Ca intake the elevated rate of Ca absorption from the caecum in RS-fed rats was not paralleled by an enhanced DI-EE difference: this suggests a shift of the Ca absorption towards the large intestine. Feeding Rs diets also enhanced Mg caecal absorption, resulting in the substatntially higher DI-FE difference for Mg, especially with the 2·5 g Ca/kg diets, because a high Ca intake tends to inhibit Mg absorption. The present findings support the view that the large intestine may represent a major site of Ca (and Mg) absorption when acidic fermentations take place. This process could improve the digestive Ca balance when the dietary Ca supply is low; when the Ca supply is affluent, it rather shits Ca absorption towards a more distal site fo the digestive tract.

Sodium transport across the caecal and colonic epithelium of germfree and specific-pathogen free rats.

It was assumed that the enlarged caecum and the accumulation of semiliquid contents in germfree rats is accompanied by changes in sodium absorption. Transepithelial sodium fluxes were studied under Ussing chamber conditions across epithelial sheets of the caecum and colon of germfree (GF) and specific-pathogen free (SPF) rats. Net sodium transport was highest in the proximal colon and in the proximal segment of the distal colon; it was considerably lower in the caecum and in the distal segment of the distal colon. In the caecum and proximal colon of the GF rats, the electroneutral sodium absorption was increased as compared to the SPF rats. In the proximal segments of the distal colon, no differences were seen. In the distal segment of the distal colon, the mainly electroneutral sodium transport in the SPF rats was changed into electrogenic transport in the GF rats. These differences may be due to the increased aldosterone levels of the GF rats.

Folate absorption in the caecum of chronic ethanol-fed rats: in vivo studies.

This study was designed to determine the intestinal in vivo absorption of folic acid and methyltetrahydrofolate (MTHF) by the caecum surface at different times after 20 weeks of 30% ethanol ingestion. The absorption results were compared to the data of control rats. Chow and fluid consumption and body weight were significantly lower in ethanol-fed rats. The absorption of folic acid and MTHF by the caecum surface (pmol/cm2) was generally decreased in ethanol-fed rats at all concentrations assayed with respect to control animals (except for absorption of 0.5 and 2.5 microM folic acid at 15-min intervals). The results obtained in the present work also suggest a different absorptive behaviour of folic acid and MTHF in the caecum under the influence of chronic alcohol ingestion.

Effects of vitamin E deficiency on autonomic neuroeffector mechanisms in the rat caecum, vas deferens and urinary bladder.

1. Modified sucrose-gap, standard organ-bath techniques and transmitter release studies were used to examine neuromuscular transmission in the caecum, vas deferens and urinary bladder in normal rats and in rats maintained for 12 months on a diet free of vitamin E. 2. In the caecum circular muscle, non-adrenergic, non-cholinergic inhibitory junction potentials were absent from 48 and 15% of preparations from vitamin E-deficient and control animals, respectively. Cholinergic excitatory junction potentials were absent from 83 and 8% of vitamin E-deficient and control preparations, respectively. Responses to applied noradrenaline (0.1-30 microM), alpha,beta-methylene ATP (3-100 microM) and acetylcholine (0.1-30 microM) were attenuated or absent in vitamin E-deficient tissues. Responses to applied KCl were similar in both groups. Release of [3H]noradrenaline or endogenous acetylcholine could not be evoked from vitamin E-deficient tissues. 3. In contrast, in isolated preparations of the vas deferens and urinary bladder, neuromuscular transmission by adrenergic, cholinergic and purinergic components were unaffected by long-term vitamin E deficiency. 4. In conclusion, vitamin E deficiency causes dysfunction of autonomic neuroeffector mechanisms in the smooth muscle of the rat caecum, at both a pre- and postjunctional level. The lesions in autonomic transmission mechanisms brought about by long-term vitamin E deficiency were found only in the caecum; no changes in sympathetic neuromuscular transmission were observed in the vas deferens, or in parasympathetic neuromuscular transmission in the urinary bladder.

Intestinal site-dependent susceptibility to chronic indomethacin in the rat: a morphological and biochemical study.

The cyclo-oxygenase inhibitor indomethacin induces a pattern of gastrointestinal injury in the rat that is site-dependent. This study compared the extent of injury to different regions of the rat intestine (small intestine, caecum and colon) with the corresponding changes in arachidonic acid metabolism in these areas, following long-term, low-dose indomethachin. Rats (eight per group) received either indomethacin (3 mg.kg/day) or control diet for either 6 or 12 weeks. At termination animals were bled, examined both macroscopically and microscopically for ulcers, and assayed for blood thromboxane B2, intestinal tissue prostaglandin E2 content and production of leukotriene B4. In a further eight animals luminal indomethacin concentrations from the small intestine, caecum and colon were measured following 6 weeks of chronic drug ingestion. At 6 weeks, macroscopic ulcers were observed in 2/8 (small intestine), 3/8 (caecum) and 1/8 (colon) animals. The corresponding ratios at 12 weeks were 5/8, 8/8 and 0/8. In control animals, a site-dependent gradient of the prostaglandin E2 concentration was found. In indomethacin-dosed animals the intestinal prostaglandin E2 content was reduced significantly in the caecum at 6 weeks, and in all tissues at 12 weeks. An increased leukotriene B4 production was observed in the caecum only, at 12 weeks (P < 0.01), and the blood thromboxane B2 was reduced at both time points (P < 0.05). There is a site-dependent gradient of the prostaglandin E2 concentration in the rat intestine. The rat caecum is particularly sensitive to long-term low-dose indomethacin, both in terms of chronic intestinal inflammation and changes in prostanoid metabolism. This site-dependent degree of injury may be associated with a local cyclo-oxygenase inhibition.

Synthesis and in vitro biodegradation of poly(ether-ester) azo polymers designed for colon targeting

A number of poly(ether-ester) azo polymers consisting of various concentrations of 4-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy} benzoic acid (HEEEBA), 4-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenylazobenzoic acid (HEEEPABA) and either 12-hydroxydodecanoic or 16-hydroxyhexadecanoic acid were synthesized. The polymers were assessed in order to determine whether they are biodegradable by the azoreductase present in the rat caecum. The polymers containing HEEEBA showed satisfactory degradation (up to 48%), while those without showed poor degradation, due to poor wettability. When 1% polysorbate 80 (a wetting agent) was added to the polymers in the degradation medium, all polymers showed excellent degradation. Azo polymers with HEEEBA have the potential to be used as colon-specific drug release materials.

Short‐chain fatty acid content and pH in caecum of rats fed various sources of starch

AbstractCaecal pH and contents of short‐chain fatty acids (SCFA) were registered in rats fed three potential sources of resistant starch (RS); raw pea starch, raw potato starch, and an RS‐enriched preparation obtained from wheat starch by autoclaving and enzymatic incubation. Small intestinal digestibility and delivery of RS to the hind‐gut in the case of raw starches were determined by analysis of faecal starch in animals treated with antibiotics to prevent hind‐gut fermentation. RS content in the RS‐enriched preparation was determined as total starch remaining in an enzymatic gravimetric dietary fibre residue. The fermentability of RS was estimated from the faecal recovery of starch in normal animals with intact hind‐gut microflora. Approximately 35 g per 100 g and 32 g per 100 g were RS in the case of raw potato starch and the RS‐enriched preparation, respectively, versus only 1 g per 100 g in the case of raw pea starch. The caecal pH decreased with all test diets, being most significant with raw potato starch. SCFA production and faecal bulking were negligible with raw pea starch, whereas both raw potato starch and the RS‐enriched preparation significantly increased these parameters. The fermentability of RS in raw potato starch and the RS‐enriched preparation was similar, or about 60–70%. If calculated on basis of fermented amount, RS in raw potato starch was more potent in generating SCFA (49 μmol g−1) than in the RS‐enriched preparation (19 μmol g−1). RS in raw potato starch also displayed the highest faecal bulking capacity. In fact, the faecal dry weight increased more than expected merely from delivery of RS. The relative proportion in caecal contents of acetic‐, propionic‐ and butyric acid was 70, 17 and 8%, respectively, with no significant differences between the three sources of RS.

Interleukin-4 gene expression in mercury-induced autoimmunity.

Mercuric chloride (HgCl2) induces autoimmunity in Brown Norway (BN) rats, with necrotizing vasculitis in the gut. Circumstantial evidence implicates the Th2 subset of CD4+ T lymphocytes, which produces IL-4. We developed a quantitative polymerase chain reaction (PCR) technique to quantify IL-4 gene expression. A phagemid containing rat IL-4 cDNA was modified to act as the template for a synthetic RNA construct; a known amount of synthetic RNA was added to total RNA from spleen and caecum of BN rats at various times after HgCl2, followed by reverse transcriptase PCR. IL-4 gene expression increased markedly in spleen and caecum after HgCl2. Splenic levels peaked by 10 days at approximately five-times baseline, then returned towards normal as the autoimmune response was spontaneously regulated. Caecal IL-4 expression peaked at 48 h, at which time we observed a previously unreported early phase of tissue injury, with necrotizing vasculitis qualitatively similar to that reported previously in the later phases of the model. These data support a key role for IL-4 in this experimental model of autoimmunity. The quantitative PCR technique can be modified for analysis of other cytokines, allowing further investigation of the role of T cell subsets in this model.

Stimulation of bicarbonate secretion by α- and β-adrenoceptor agonists in rat caecum in vitro

This study examines the effects of adrenergic drugs on bicarbonate secretion by the rat caecum in vitro. Noradrenaline, phenylephrine but not clonidine, stimulated secretion in a concentration-related manner. Noradrenaline responses were antagonised by alprenolol (20 μm) but not phentolamine (10 μM) whilst phenylephrine was antagonised by phentolamine (10 μM), prazosin (5 μM) but not yohimbine (5 μM), alprenolol or tetrodotoxin (1 μM). Replacement of mucosal Cl − abolished the phenylephrine response. Combined stimulation with maximum concentrations of phenylephrine and isoprenaline gave a response which was not greater than that to either agonist alone but it did involve both α- and β-adrenoceptors as judged from the effects of alprenolol and phentolamine either alone or combined. Submaximum concentrations of the two agonists did show additive responses. The results show that α 1- but not α 2-adrenoceptor agonists stimulate bicarbonate secretion and may act on the same transport mechanism as β-adrenoceptor agonists. Noradrenaline stimulates via β-adrenoceptors.

Tubulovesicular elements in Blastocystis hominis from the caecum of experimentally-infected rats

By transmission electron microscopy (TEM), tubulovesicular elements were seen in Blastocystis hominis obtained from the caecum of experimentally-infected rats. These appeared to arise from the peripheral cytoplasm and were rounded, oval or elongate in sections. It is suggested that these elements form a network for transfer of nutrients to the periphery during the process of encystation.

Breakdown of amylomaize starch granules in gnotobiotic rats associated with four bacterial strains isolated from conventional rat microflora

AbstractBalance studies in germ‐free (GF) and conventional (CV) rats have shown that in‐vivo breakdown of amylomaize starch depends on endogenous and bacterial enzymes. In GF rats, one‐third of amylomaize starch is resistant to endogeneous digestion, whereas in CV rats starch is totally degraded, In order to study the contribution of endogenous and bacterial enzymes, the in‐vivo breakdown of amylomaize starch was compared in GF and in gnotobiotic rate associated with bacterial strains isolated from the conventional rat microflora. These bacteria were (i) a non‐amylolytic Peptostreptococcus (GNP rats),(ii) an amylolytic strain of Eubacterium able to hydrolyse resistant starch (GNE rats), and (iii) an association of Eubacterium with three other bacterial strains (Veillonella, Enterococcus and Peptostreptococcus) able to ferment the products of starch hydrolysis (GNT rats). Various studies were performed to assess the starch breakdown in the caecal contents: balance studies, light and electron microscopy and analyses of bacterial metabolites. The results show that in GNP as in GF rate, around 65% of amylomaize starch was resistant to digestion. Digestive utilization of starch was significantly improved in GNE rats (from 68 to 92%) and was further enhanced to 97% in GNT rats. The increase in starch degradation in the caecum of rats was related to a higher amylase activity and led to an increase in production of bacterial metabolites, and to a change in the proportions of short‐chain fatty acids, lactic acid and succinic acid, infrastructure study of the starch in the caecal contents showed a progressive granule hydrolysis in the order GF, GNE and GNT rats: (i) an endocorrosion of the central part of the starch granules in GF rats, (ii) a peripheral digestion with bacteria penetrating the granules in GNE rats, and (iii) a more pronounced hydrolysis in the caecum of GNT rats where the outer part of the granules were almost entirely hydro‐lysed. These results suggest that starch breakdown in the hindgut is not only due to amylolytic bacteria but also to the contribution of other glycolytic strains able to utilize the products of starch hydrolysis.

Ulceration, fibrosis and diaphragm‐like lesions in the caecum of rats treated with indomethacin

Patients on nonsteroidal anti-inflammatory drugs can develop curious intestinal fibrotic diaphragms. Groups of rats received indomethacin mixed into a powdered diet at 3 mg.kg/day for 6 and 12 weeks and 6 mg.kg/day for up to 6 weeks. In an attempt to reproduce a human dosing regimen, another group of rats, for a total of 30 weeks, received consecutive periods of indomethacin at 3 mg.kg/day for 12 weeks, 4.5 mg.kg/day for 1 week, 6 mg.kg/day for 1 week, control diet for 6 weeks, 4.5 mg.kg/day for 2 weeks and finally, a control diet for a healing period of 8 weeks. Control rats received powdered diet alone. At termination, the small and large intestines were examined macroscopically and histologically. Indomethacin caused microcytic anaemia, hypoalbuminaemia, small intestinal ulceration, caecal ulceration and inconspicuous raised mucosal lesions in the caecum that histologically showed submucosal fibrosis with disruption and thickening of the apical muscularis mucosae. No control rats showed any abnormality. These fibrotic lesions of the rat caecum resemble human diaphragms and may arise from healed caecal ulcers.

A novel Mutein of TNFα Containing the Arg‐Gly‐Asp Sequence Shows Reduced Toxicity in Intestine

The effects of human tumour necrosis factor-α (TNFα), or its mutein (F4168) having the cell adhesive Arg-Gly-Asp sequence at the N-terminus, on intestinal injury, were examined. Histopathological examination revealed that an intravenous injection of TNFα resulted in marked haemorrhage or oedema in the caecum of rats, whereas F4168 showed no such effects even at the same therapeutic dose. Moreover, the number of neutrophils that adhered to endothelial cells or infiltrated the mucosal tissue was much higher after TNFα injection compared with F4168 in vivo. The enhanced adhesion of neutrophils on to human umbilical vein endothelial cells also occurred when the latter were pre-stimulated with TNFα but not with F4168 in vitro. The expression of the cell adhesion molecules including endothelial leukocyte adhesion molecule-1 or intercellular adhesion molecule-1 on F4168- stimulated human umbilical vein endothelial ceils was significantly lower than that stimulated with TNFα. These results suggest that the Arg-Gly-Asp sequence introduced into the TNFα molecule abrogates the side effect of this cytokine such as tissue injury or shock, and that F4168 could be useful for systemic therapy.

Intestinal lipid metabolism in suckling rats infected withGiardia duodenalis

We carried out a quantitative and qualitative analysis of intestinal digestion of neutral lipids in suckling rats infected with Giardia duodenalis. Total lipids were measured after extraction from the contents of the stomach, proximal and distal small bowel, caecum and colon. Amounts gradually fell from the stomach to the colon and were identical in infected animals and controls, although high values were occasionally found in the caecum of infected rats. Relative glyceride quantities were determined by means of high-performance thin-layer chromatography. Triglycerides were absent from the distal small bowel, and only free fatty acids and cholesterol were present in the caecum, reflecting normal digestion of neutral lipids in infected suckling rats. Our results suggest that G. duodenalis does not impair intestinal fat digestion in suckling rats.

Effects of galacto-oligosaccharide and bacterial status on mucin distribution in mucosa and on large intestine fermentation in rats

The purpose of the present paper was to study the effects of a dietary undigestible carbohydrate and intestinal microflora on mucin distribution (neutral, acid, sulphonated), glycolytic activities: beta-D-galactosidase (EC 3.2.1.23), N-acetyl-beta-D-galactosaminidase (EC 3.2.1.43), N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), alpha-L-fucosidase (EC 3.2.1.51) and bacterial metabolism (gas production, short-chain fatty acids (SCFA) and lactic acid caecal concentration) in germ-free (GF), conventional (CV) and heteroxenic (HE) rats (GF rats associated with a human flora). Rats were fed on either a control diet or a diet containing 40 g trans-galactosylated oligosaccharide (TOS)/kg. In GF rats fed on the control diet caecal pH was almost neutral and glycolytic activities negligible. The number of mucus-containing cells increased from the caecum to the colon for the three types of mucin. TOS had no effect in the caecum but it modified mucin cell repartition in the colon. In CV and HE rats fed on the control diet caecal pH was similar (6.8), but caecal SCFA and lactic acid concentrations (mumol/g) and gas production (ml/24 h) were higher in CV (70, 5.9 and 2.3 respectively) than in HE rats (32, 4.6 and 0.4 respectively). In CV, as in HE rats, acid-mucin-containing cells increased from the caecum to the colon and glycolytic activities were similar. TOS reduced acid-mucin-containing cells in the caecum of CV rats by twofold but had no effect in either the caecum or the colon of HE rats. TOS strongly increased beta-galactosidase activity and slightly modified the other glycolytic activities. Its effect on bacterial metabolites depended on bacterial status. However, comparison between CV and HE rats showed no evident relationship between the number of mucus-containing cells and measured bacterial metabolites. Differences between CV and HE rats might be due to bacterial microflora specificity. TOS had an intrinsic effect on mucus cell distribution in the colon of GF rats. In CV and HE rats the presence of the flora abolished this effect.

Short‐chain fatty acid content and pH in caecum of rats given various sources of carbohydrates

AbstractThe caecal content of short‐chain fatty acids (SCFA; acetic, propionic and butyric acid), caecal pH, fermentability and dry matter digestibility (DMD) were examined through balance experiments in rats fed 11 various indigestible carbohydrates. The following carbohydrate sources were incorporated into test diets: cellulose, oat husk, wheat bran, oat bran, pea fibre, linseed fibre, low methoxylated (LM)‐pectin, guargum, β‐glucans, neosugar and raffinose. The indigestible carbohydrates, except for those in wheat bran, oat husk and cellulose, were highly fermented, ie &gt; 90%. Caecal pH varied between 5·6 and 7·8, with neosugar and raffinose causing the lowest pH and the fibre‐free diet and the diet with oat husk the highest. The caecal pool sizes of SCFA were highest with raffinose, β‐glucans, LM‐pectin, guargum and linseed fibre (335‐400 μmol) while pea fibre, wheat bran, oat bran and neosugar gave intermediate levels (137–227 μmol). The pool size with oat husk and cellulose was similar as with the basal diet (45–64 μmol). A high proportion of propionic acid was obtained with guargum and linseed fibre, whereas acetic acid was the predominant product in case of LM‐pectin. On the other hand, linseed fibre gave a remarkably low proportion of butyric acid. The quantity fermented and caecal pH correlated well to the amount of SCFA with most materials (r = 0·96 and r = −0·87, respectively), an exception was neosugar and in case of fermentability also oat bran. DMD values with most of the easily fermented carbohydrates were high (&gt;96%). Exceptions were diets with β‐glucans and oat bran which caused low DMD values, about 93%. It is concluded that indigestible carbohydrates may differ in ability to lower caecal pH and to form SCFA during fermentation.

Bioavailability of new synthesised glucooligosaccharides in the intestinal tract of gnotobiotic rats

AbstractUsing germ‐free rats and previously germ‐free rats inoculated with a complex human flora (heteroxenic rats), the digestibility of new glucooligosaccharides (GOS) and the effect of the digestive flora on their fermentation were studied. The GOS were synthesized using a glucosyltransferase reaction and were composed of a mixture of mono‐ to heptasaccharides (degree of polymerisation (DP) from 1 to 7), with α‐1,6 and α‐1,2 linkages. In germ‐free rats, two diets containing GOS (20 g kg−1 diet and 40 g kg−1 diet) were compared to a control diet containing sucrose. The extent of GOS digestion was about 20% and the major component, DP 5, was almost fully resistant to the action of endogenous enzymes. In heteroxenic rats, only GOS (20 g kg−1 diet) was compared to the control diet. Gaseous H2 and CH4 excretions measured in a respiratory chamber significantly increased by GOS fermentation (1.8 and 2.9 times, respectively, P &lt; 0.001). As compared to the control group, there were no modifications of the pH, short‐chain fatty acids (SCFA), and lactic acid concentrations in the caecum of rats fed with the GOS diet, but there were changes of the SCFA profile, ie butyric, isobutyric and isovaleric acid proportions significantly decreased (P &lt; 0.01), whereas the caproic acid proportion increased (P &lt; 0.05). GOS appeared to be completely fermented. Changes in the gaseous excretion and in the SCFA profile suggest that the intake of a low amount of this new synthetised GOS led to some decrease in the proteolytic activity and in an enhancement of the glycolytic fermentation.