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Objectives: Non-invasive biomarkers which identify different mechanisms of disease in subgroups of irritable bowel syndrome (IBS) could be valuable. Our aim was to seek useful magnetic resonance imaging (MRI) parameters that could distinguish each IBS subtypes., Methods: 34 healthy volunteers (HV), 30 IBS with diarrhea (IBS-D), 16 IBS with constipation (IBS-C), and 11 IBS with mixed bowel habit (IBS-M) underwent whole-gut transit and small and large bowel volumes assessment with MRI scans from t=0 to t=360 min. Since the bowel frequency for IBS-M were similar to IBS-D, IBS-M and IBS-D were grouped together and labeled as IBS non-constipation group (IBS-nonC)., Results: Median (interquartile range): fasting small bowel water content in IBS-nonC was 21 (10-42), significantly less than HV at 44 ml (15-70), P<0.01 as was the postprandial area under the curve (AUC) P<0.01. The fasting transverse colon volumes in IBS-C were significantly larger at 253 (200-329) compared with HV, IBS-nonC whose values were 165 (117-255) and 198 (106-270) ml, respectively, P=0.02. Whole-gut transit time for IBS-C was prolonged at 69 (51-111), compared with HV at 34 (4-63) and IBS-D at 34 (17-78) h, P=0.03. Bloating score (VAS 0-10 cm) correlated with transverse colon volume at t=405 min, Spearman r=0.21, P=0.04., Conclusions: The constricted small bowel in IBS-nonC and the dilated transverse colon in IBS-C point to significant differences in underlying mechanisms of disease.

Background: Poorly absorbed fermentable carbohydrates can provoke irritable bowel syndrome (IBS) symptoms by escaping absorption in the small bowel and being rapidly fermented in the colon in some susceptible subjects. IBS patients often are anxious and stressed, and stress accelerates small bowel transit, which may exacerbate malabsorption. Objective: In this study we investigated the effect of an intravenous injection of corticotropin-releasing factor (CRF) on fructose malabsorption and the resulting volume of water in the small bowel. Design: We performed a randomized, placebo-controlled crossover study of CRF compared with saline injection in 11 male and 10 female healthy subjects, examining the effect on the malabsorption of a 40-g fructose test meal and its transit through the gut, which was assessed by serial MRI and breath hydrogen measurement. Orocecal transit was assessed with the use of the lactose [13C]ureide breath test and the adrenal response to CRF was assessed by serial salivary cortisol measurements. Results: CRF injection caused a significant increase in salivary cortisol, which lasted for 135 min. Small bowel water content (SBWC) rose from baseline, peaking at 45 min after fructose ingestion, whereas breath hydrogen peaked later, at 75 min. The area under the curve for SBWC from –15 min to 135 min was significantly lower after CRF compared with saline [mean difference: 5911 mL · min (95% CI: 18.4, 11,803 mL · min), P = 0.049]. Considering all subjects, the percentage change in ascending colon volume rose significantly after CRF. This increase was significant for male (P = 0.026), but not female, volunteers. Conclusions: CRF constricts the small bowel and increases fructose malabsorption, as shown by increased ascending colon volumes. This mechanism may help to explain the increased sensitivity of some stressed individuals to fructose malabsorption. This trial was registered at clinicaltrials.gov as NCT01763281. [ABSTRACT FROM AUTHOR]