83 They stimulate absorption of water see more and electrolytes and thereby prevent diarrhea.83 Colonic acidification by SCFA may increase its motility.85 In contrast, motility of proximal gut by SCFA is reduced due to induction of the ileal brake;84 as a result, reduced proximal gut motility may predispose to SIBO. Bacteria in the small intestine in patients with SIBO produce SCFA and deconjugate bile acids.86 These may contribute to diarrhea in patients with SIBO. Bacterial fermentation and production of various gases may contribute to the pathogenesis IBS and its symptoms. A study by Pimentel et al. from the USA reported
that 12 (39%) of 31 constipation-predominant IBS patients excreted methane, whereas none of 34 diarrhea-predominant patients were methane excreters.87 This led to a hypothesis that
methane gas produced by bacteria may contribute to the development of constipation in patients with IBS.88 In dogs, luminal methane infusion compared with room air infusion significantly reduced intestinal transit.17 Exposing tissues to methane also increased the force of contractions in response to mucosal stimulation; the authors therefore suggested that methane predisposes to constipation via promotion of segmental, non-propagating contractions.17 In a study in guinea pigs, the amplitude of peristaltic contraction was significantly decreased when hydrogen was infused, whereas it was significantly RAD001 increased in the methane infusion group.89 Further, peristaltic velocity was significantly delayed after methane infusion.89 The area under curve of intra-luminal pressure was also markedly increased after infusion of methane. These results support the concept that methane promotes non-propagating or segmental contractions of the selleck inhibitor small bowel. This study provides an experimental basis for verifying that there
is a significant correlation between methane producers and constipation-predominant IBS.89 Some authors have hypothesized that methanogenic flora may reduce flatulence; as one molecule of carbon dioxide combines with four molecules of hydrogen to produce one molecule of methane, it may result in reduction of total volume of gas in the gut.58 In an Indian study, predominant methanogenic flora (fasting methane concentration > 10 ppm) was present in 50/345 (14.5%) patients with IBS diagnosed by Rome II criteria as compared with 88/254 (34.6%) of healthy controls.58 These studies suggest that the gut flora and the gas produced by it may play a role in the pathogenesis of IBS symptoms, but more studies are needed to resolve this issue. Neuroendocrine factors are important mechanisms of control of sensorimotor functions by the gut flora. Ileal brake is a physiological phenomenon, in which the presence of fat or products of its digestion such as fatty acids reduces motility of proximal small intestine.