Short-chain fatty acids do not alter jejunal motility in man

Short-chain fatty acids augment rat duodenal mucosal barrier function

NEW FINDINGS

What is the central question of this study? Small intestinal epithelium is exposed to high concentrations of short-chain fatty acids (SCFAs), but their role in regulating intestinal mucosal barrier function and motility is not fully understood. What is the main finding and its importance? By perfusing the duodenal segment in anaesthetized rats, we show that acetate and propionate significantly decrease mucosal paracellular permeability and transepithelial net fluid flux and increase mucosal bicarbonate secretion. Likewise, SCFAs administered i.v. decrease mucosal permeability but decrease bicarbonate secretion. Altered luminal chemosensing or aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed mucosal barrier function. Short-chain fatty acids (SCFAs) are produced by bacterial fermentation in the large intestine, particularly from diets containing fibres and carbohydrates. The small intestinal epithelium is exposed to SCFAs derived mainly from oral bacteria or food supplementation. Although luminal nutrients are important in regulation of intestinal functions, the role of SCFAs in regulation of small intestinal mucosal barrier function and motility has not been fully described. The aim of the present study was to elucidate the effects of acetate and propionate on duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30 mm segment of proximal duodenum with an intact blood supply was perfused. The effects on duodenal bicarbonate secretion, blood-to-lumen clearance of ⁵¹ Cr-EDTA, motility and transepithelial net fluid flux were investigated. Perfusion of the duodenum with acetate or propionate significantly decreased mucosal paracellular permeability and transepithelial net fluid flux and significantly increased bicarbonate secretion. Acetate or propionate administered as an i.v. infusion decreased the mucosal paracellular permeability, but significantly decreased bicarbonate secretion. Luminal SCFAs changed the duodenal motility pattern from migrating motor complexes to fed patterns. Systemic administration of glucagon-like peptide-2 induced increases in both bicarbonate secretion and net fluid absorption, but did not change motility. Glucagon-like peptide-2 infusion during luminal perfusion of SCFAs significantly reduced the motility. In conclusion, SCFAs decreased duodenal paracellular permeability and net fluid flux. Short-chain fatty acids induced opposite effects on bicarbonate secretion after luminal and i.v. administration. Presence of SCFAs in the lumen induces fed motility patterns. Altered luminal chemosensing and aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed barrier function.

Effect of short-chain fatty acids and acidification on the phasic and tonic motor activity of the human colon

BACKGROUND

The effects of bacterial fermentation on human colonic motor activity could be explained by colonic acidification or short-chain fatty acid (SCFA) production. We compared in healthy volunteers the colonic motor effects of intracolonic infusion of neutral or acidic saline solutions and then of neutral or acidic solutions containing an SCFA mixture.

METHODS

20 healthy volunteers swallowed a probe (with an infusion catheter, 6 perfused catheters and a balloon connected to a barostat) that migrated into the colon. Colonic motor activity was recorded in fasting basal state (1 h), during (3 h) and after (2 h) intracolonic infusion in a random order on two consecutive days of 750 mL of NaCl at pH 7.0 (neutral saline) or 4.5 (acidic saline) in 10 volunteers (first experiment) and of an SCFA mixture (acetic acid 66%, propionic acid 24% and butyric acid 10%; 100 mM) at pH 7.0 or 4.5 in 10 other volunteers (second experiment). We determined for each hour a global motility index (reflecting phasic activity recorded by all catheters), the mean balloon volume (reflecting tonic activity), and the mean number of high-amplitude-propagated contractions (HAPCs).

KEY RESULTS

Intracolonic infusion of neutral or acidic solutions containing saline or an SCFA mixture did not change the global motility index, the barostat balloon volume, or the HAPC number compared with basal values.

CONCLUSIONS & INFERENCES

Under our experimental conditions, these findings suggest that the stimulation of colonic motor activity induced by carbohydrate fermentation is not explained by the acidification of the colonic contents or the resulting production of SCFAs.

Butyrylated starch increases large bowel butyrate levels and lowers colonic smooth muscle contractility in rats

The short-chain fatty acids acetate, propionate, and butyrate are produced by colonic bacterial fermentation of carbohydrates. Butyrate is important in the regulation of the colonocyte cell cycle and gut motility and may also reduce the risk of large bowel cancer. We have shown that dietary butyrylated starch can deliver butyrate to the large bowel in a sustained manner. We hypothesized that ingestion of butyrylated starch increases large bowel butyrate levels and decreases colonic contractility. Groups of male Sprague-Dawley rats (n = 8) were fed AIN-93G-based diet containing a highly digestible low-amylose maize starch (LAMS) control or 5% or 10% butyrylated LAMS (LAMSB) for 10 days. We found that cecal but not colonic tissue weight as well as cecal and distal colonic digesta weights and fecal output were higher in LAMSB fed rats. Butyrylated LAMS lowered digesta pH throughout the large bowel. Cecal, proximal, and distal colonic butyrate pools and portal venous butyrate concentrations were higher in rats fed LAMSB. Electrically stimulated and receptor-dependent carbachol and prostaglandin E(2)-induced isotonic contractions were lower in isolated intact sections of proximal colon (P < .05) but not the terminal ileum after 10% LAMSB ingestion. These results demonstrated that elevation of butyrate levels in the large bowel of the rat correlated with reduction of contractile activity of the colonic musculature, which may assist in the reabsorption of water and minerals.

The relationship between the effects of short-chain fatty acids on intestinal motility in vitro and GPR43 receptor activation

The G protein-coupled receptors, GPR41 and GPR43, are activated by short-chain fatty acids (SCFAs), with distinct rank order potencies. This study investigated the possibility that SCFAs modulate intestinal motility via these receptors. Luminal SCFA concentrations within the rat intestine were greatest in the caecum (c. 115 mmol L(-1)) and proximal colon. Using similar concentrations (0.1-100 mmol L(-1)), SCFAs were found to inhibit electrically evoked, neuronally mediated contractions of rat distal colon, possibly via a prejunctional site of action; this activity was independent of the presence or absence of the mucosa. By contrast, SCFAs reduced the amplitude but also reduced the threshold and increased the frequency of peristaltic contractions in guinea-pig terminal ileum. In each model, the rank-order of activity was acetate (C2) approximately propionate (C3) approximately butyrate (C4) > pentanoate (C5) approximately formate (C1), consistent with activity at the GPR43 receptor. GPR43 mRNA was expressed throughout the rat gut, with highest levels in the colon. However, the ability of SCFAs to inhibit neuronally mediated contractions of the colon was similar in tissues from wild-type and GPR43 gene knockout mice, with identical rank-orders of potency. In conclusion, SCFAs can modulate intestinal motility, but these effects can be independent of the GPR43 receptor.

Influence of microbial species on small intestinal myoelectric activity and transit in germ-free rats

The effect of an intestinal microflora consisting of selected microbial species on myoelectric activity of small intestine was studied using germ-free rat models, with recording before and after specific intestinal colonization, in the unanesthetized state. Intestinal transit, neuropeptides in blood (RIA), and neuromessengers in the intestinal wall were determined. Clostridium tabificum vp 04 promoted regular spike burst activity, shown by a reduction of the migrating myoelectric complex (MMC) period from 30.5 +/- 3.9 min in the germ-free state to 21.2 +/- 0.14 min (P < 0.01). Lactobacillus acidophilus A10 and Bifidobacterium bifidum B11 reduced the MMC period from 27.9 +/- 4.5 to 21.5 +/- 2.1 min (P < 0.02) and accelerated small intestinal transit (P < 0.05). Micrococcus luteus showed an inhibitory effect, with an MMC period of 35.9 +/- 9.3 min compared with 27.7 +/- 6.3 min in germ-free rats (P < 0.01). Inhibition was indicated also for Escherichia coli X7 gnotobiotic rats. No consistent changes in slow wave frequency were observed. The concentration of neuropeptide Y in blood decreased after introduction of conventional intestinal microflora, suggesting reduced inhibitory control. Intestinal bacteria promote or suppress the initiation and aboral migration of the MMC depending on the species involved. Bacteria with primitive fermenting metabolism (anaerobes) emerge as important promoters of regular spike burst activity in small intestine.

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.

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.

In vitro contractile effects of short chain fatty acids in the rat terminal ileum

Short chain fatty acids (SCFAs), produced in the gut by bacterial fermentation of carbohydrates, change intestinal motility by mechanisms as yet unknown. This study examined the mechanism(s) of action of SCFAs on contractility using isolated rat terminal ileum segments and isolated ileal smooth muscle cells. Strip contractions were recorded under isometric conditions. Intracellular calcium concentration ([Ca2+]i) was measured in single cells loaded with indo-1 penta-acetoxymethyl ester (indo-1 AM). SCFAs (10(-9) to 10(-2) mol/l) induced concentration dependent contractions. The effect was not different among the individual SCFAs. Exogenous acids (namely tartaric and citric acids) caused similar responses as SCFAs, whereas sodium acetate had no effect. The contraction was not blocked by tetrodotoxin, atropine or hexamethonium, showing that it was not mediated through a cholinergic pathway. Moreover, removal of the mucosa or addition of procaine (a local anaesthetic) to the bath did not change the SCFA induced contraction, while verapamil (a calcium-channel antagonist) completely suppressed it. In addition, application of SCFAs to isolated ileal myocytes evoked peaks in [Ca2+]i inhibited by D 600 (a blocker of voltage dependent calcium channels). Taken together, these results suggest that the contractile response stimulated by SCFAs in the rat terminal ileum could result from an acid sensitive calcium dependent myogenic mechanism.

Abnormal intestinal motor patterns explain enteric colonization with gram-negative bacilli in late radiation enteropathy

BACKGROUND & AIMS

Bacterial overgrowth and intestinal pseudo-obstruction may succeed abdominal radiotherapy, and absence of intestinal migrating motor complex (MMC) has been reported in bacterial overgrowth. The aims of this study were to address the relationship between intestinal patterns of motility and gastrointestinal microflora and to elucidate the pathogenesis of late radiation enteropathy.

METHODS

Forty-one consecutive female patients with symptoms of late radiation enteropathy were examined by prolonged ambulatory manometry, culture of gastric and duodenal samples with quantification of gram-negative bacilli (GNB) by the glucose gas test, the [14C]D-xylose breath test, and determination of pH and short-chain fatty acids in gastric juice.

RESULTS

The intensity of MMC explained 61% (P < 0.001) and 71% (P < 0.001) of the variability of GNB in the stomach and duodenum, respectively, corresponding to the severity of disease. Abnormal MMC index and presence of irregular bursts were the best predictors of GNB (86%; P < 0.001, multiple regression). Fasting gastric pH explained gastric bacterial counts (63%; P < 0.001) but did not predict GNB.

CONCLUSIONS

Impaired motility emerges as a causal factor for gastrointestinal colonization with GNB, whereas hypochlorhydria facilitates unspecific gastric colonization. Abnormal motility and GNB in the proximal small intestine are essential factors in the pathogenesis of severe late radiation enteropathy.

The motor response to intestinal resection: motor activity in the canine small intestine following distal resection

BACKGROUND

The mucosal response to intestinal resection has been extensively studied; little is known of the motor response. Our aim was to evaluate motility in the intestinal remnant following distal resection.

METHODS

Motor activity, duodenocecal transit, nutrition, and absorption were studied over a 3-month period in control animals (n = 9) and in groups of dogs who had undergone 25% (n = 6), 50% (n = 5), and 75% (n = 5) distal resection.

RESULTS

Diarrhea and steatorrhea developed in each resection group, and the 75% group alone developed true short bowel syndrome. Resection did not affect migrating motor complex frequency or periodicity; phase 1 duration was shorter in the 75% group (control vs. 75%: 22 +/- 4 vs. 6 +/- 2 minutes, P < 0.03). The most striking motor effect was the development of prominent cluster activity in the distal part of the remnant in 25% and 50% resection animals and throughout the remaining intestine in the 75% group. Duodenocecal transit slowed during the study period from 13 +/- 1 to 20 +/- 2 minutes in the 50% and from 10 +/- 2 to 14 +/- 2 minutes in the 75% group (P < 0.05).

CONCLUSIONS

The initial motor response to major resections of the distal small intestine is dominated by the development of abnormal patterns. This motor disruption may contribute to the symptomatology and clinical features of the short bowel syndrome.