Duodenal motility in fasting dogs: humoral and neural pathways mediating the colonic brake

Carbohydrates designed with different digestion rates modulate gastric emptying response in rats

We sought to determine whether design of carbohydrate-based microspheres to have different digestion rates, while retaining the same material properties, could modulate gastric emptying through the ileal brake. Microspheres made to have three slow digestion rates and a rapidly digested starch analogue (maltodextrin) were administrated to rats by gavage and starch contents in the stomach, proximal and distal small intestine, and caecum were measured 2 h post-gavage. A stepwise increase in the amount of starch retained in the stomach was found for microspheres with incrementally slower rates of digestion. Postprandial glycaemic and insulinaemic responses were incrementally lower for the different microspheres than for the rapidly digestible control. A second-meal effect was observed for slowly digestible starch (SDS) microspheres compared to glucose. Thus, dietary slowly digestible carbohydrates were designed to elicit incremental significant changes in gastric emptying, glycaemic and insulinaemic responses, and they may be a means to trigger the ileal brake.

Distal Colon Motor Dysfunction in Mice with Chronic Kidney Disease: Putative Role of Uremic Toxins

Although gastrointestinal complications are a common feature of patients with chronic kidney disease (CKD), the impact of uremia on bowel motility remains poorly understood. The present study was, therefore, designed to investigate the impact of uremia on gut motility. Kidney failure was induced in mice by chemical nephrectomy using an adenine diet (0.25% w/w). Gastrointestinal transit time and colon motility were explored in vivo and ex vivo. Colons from control mice were incubated with uremic plasma or uremic toxins (urea, indoxyl-sulfate or p-cresyl-sulfate) at concentrations encountered in patients with end-stage renal disease. Mice fed an adenine diet for 3 weeks exhibited a 3-fold increase in plasma urea (p < 0.001) evidencing kidney failure. The median gastrointestinal transit time was doubled (1.8-fold, p < 0.001) while a reduction in colonic propulsive motility was observed in CKD mice (3-fold, p < 0.001). Colon from CKD mice exhibited an abnormal pattern of contraction associated with a blunted maximal force of contraction. Control colons incubated with plasma from hemodialysis patients exhibited a blunted level of maximal contraction (p < 0.01). Incubation with urea did not elicit any difference but incubation with indoxyl-sulfate or p-cresyl-sulfate decreased the maximal force of contraction (−66% and −55%, respectively. p < 0.01). Taken together, these data suggest that uremia impairs colon motility probably through the retention of uremic toxins. Colon dysmotility might contribute to the gastrointestinal symptoms often reported in patients with CKD.

Propagation of giant migrating contractions between the small intestine, cecum and colon during radiation

BACKGROUND

Radiation increases the frequency of small intestinal and colonic giant migrating contractions (GMCs). These contractions contribute to the diarrhea and cramping after radiation therapy and are coordinated with one another across the ileocolonic (IC) junction.

METHODS

We investigated the coordination of contractile activity between the small intestine, cecum and colon in five canines following circumferential myotomy on the ileum at the IC junction and compared it to intact animals. Studies were performed before and during a radiation schedule.

KEY RESULTS

Myotomy increased the frequency of small intestinal GMCs prior to irradiation. In intact animals, the duration and amplitude of cecal GMCs decreased when multiple contractions occurred in rapid succession. This is in contrast to small intestinal and colonic GMCs and suggests a different mechanism of propagation for GMCs within the cecum. Ileal myotomy dramatically decreased the frequency of propagating radiation-induced colonic GMCs. The total number of colonic GMCs was not altered. Colonic contractile activity was disrupted in intact animals during irradiation. However, after ileal myotomy, irradiation did not affect the pattern of colonic contractile states. Diarrhea in irradiated animals with myotomy started earlier than intact animals. This may be related to the frequency of small intestinal GMCs.

CONCLUSIONS & INFERENCES

Our findings suggest importance of the enteric neural connections at the IC region to contractile disorders of both the small and large intestine. The anatomic relationship between the canine IC junction is similar to the human ileo-appendiceal-colonic region and surgical manipulations of this area may likewise affect human contractile activity.

The effect of a total colectomy on the motor inhibition of the upper gut induced by intraileal stimuli in conscious dogs

PURPOSE

The administration of stimuli to the ileum inhibits upper gastrointestinal motility. The aim of this study was to determine whether a total colectomy can alter this motor inhibitory effect.

METHODS

Beagle dogs were each equipped with four strain gauge force transducers on the upper gastrointestinal tract. The infusion of nutrients (saline as placebo control, oleate, butyrate, and glucose) began 90 min after feeding and continued for 30 min via a silicone catheter placed in the ileal lumen. Capsaicin (10 mg) was injected into the ileum as a bolus. All of the dogs underwent a relaparotomy and a total colectomy, and the same experiments were performed on all dogs.

RESULTS

Before performing a colectomy, the oleate, the glucose, and the capsaicin were each found to inhibit the postprandial upper gastrointestinal motility in comparison to the placebo control (P < 0.05). The butyrate had no inhibitory effect. After a total colectomy, the inhibition of upper gastrointestinal motility was observed after the intraileal infusion of the oleate and the capsaicin (P < 0.05). The motor inhibitory response to the intraileal glucose was delayed after a total colectomy, and a reduction of the motility index was not observed in the gastric antrum and the duodenum because of this delay. However, a significant reduction in the motility index was observed in the jejunum.

CONCLUSION

The intraileal stimuli-induced motor inhibition decreased after a total colectomy after the administration of glucose, but not after the administration of either oleate or capsaicin.

Role of extrinsic innervation in modulating nitrergic transmission in the canine ileocolonic region

The human colon can dilate, often to life-threatening proportions. Our aim was to explore nitrergic mechanisms underlying colonic dilation in conscious dogs with enterically isolated ileocolonic loops either extrinsically innervated (n = 4) or extrinsically denervated (n = 4). We recorded phasic pressures in ileum and ileocolonic sphincter (ICS), colonic tone, compliance, and relaxation during ileal distension. By NADPH-diaphorase histochemistry, we assessed effects of extrinsic denervation and enteric isolation on nitrergic fibers. Extrinsic denervation increased phasic pressures in ileum, ICS, and colon and abolished ICS and colonic relaxation in response to ileal distension. The nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) increased phasic pressures at all sites and ICS tone but did not abolish colonic relaxation during ileal distension in innervated loops. L-NNA reduced compliance and induced colonic high-amplitude propagated contractions in denervated loops. The NOS substrate donor L-arginine reversed effects of L-NNA. The number of NADPH-diaphorase fibers increased in both enterically isolated preparations. Nonnitrergic extrinsic nerve pathways mediate reflex colonic relaxation during ileal distension. Enteric isolation augments the number of NOS fibers, an effect not modified by extrinsic denervation.

The ileal brake: a fifteen-year progress report

The "ileal brake" is the primary inhibitory feedback mechanism to control transit of a meal through the gastrointestinal tract in order to optimize nutrient digestion and absorption. Neurohormonal factors mediating this response continue to be identified. Recently, additional brakes that fine-tune transit have been described. When gut traffic control is disrupted, pathologic states characterized by malabsorption and impaired drug bioavailability manifest as diarrhea and malnutrition. An understanding of the importance of these nutrient-triggered brakes provides essential clues to future treatments of chronic diarrhea, malnutrition, and drug malabsorption.