Effect of enteric nonnutrient infusions on motor patterns in neurally intact and neurally isolated canine jejunum

The effect of osmolarity and caloric load on small bowel motility

BACKGROUND

Although there is profound knowledge about cyclic fasting motility, the postprandial intestinal motor response is not well investigated. It is intriguing to speculate that nutrient composition alters small bowel motility significantly and, in a clinical setting, may account for adverse gastrointestinal symptoms in enteral nutrition (EN). We aimed to assess the impact of different caloric loads and osmolarities of EN on human jejunal motility.

METHODS

Sixteen healthy subjects underwent a series of duodenal infusions of EN solutions, either with iso-osmolar solution with different caloric loads (1.32, 2.64, or 3.96 kcal min(-1)), or with solutions of different osmolarities with constant caloric loads (300, 600, or 1200 mosmol). Jejunal solid-state manometry was analyzed over 90 min both visually and using dedicated computer software.

KEY RESULTS

All tested nutrient solutions were able to trigger conversion to a postprandial jejunal motility pattern after a mean lag phase of 9.4 + 2.3 min (P = NS between different nutrient solutions). Different caloric loads did not result in significant differences in small bowel motility. However, increasing osmolarities caused a significant inhibition of contractile and propagative activity.

CONCLUSIONS & INFERENCES

Small bowel motility under duodenal infusion of nutrient solutions is not influenced by caloric load in a physiological range, whereas high osmolarities inhibit small bowel motility.

Extrinsic denervation alters postprandial absorption of glucose and glutamine in the ileum: implications for small bowel transplantation

In the postprandial period, augmentation of absorption of water, electrolytes, and taurocholate is believed to occur in the ileum. The role of extrinsic innervation in this postprandial augmentation has not been well studied and may be an important concept in small bowel transplantation. Our aim was to investigate extrinsic neural mechanisms mediating postprandial absorptive patterns. The study hypothesis was that postprandial augmentation of absorption in the ileum is blunted in transplanted (extrinsically denervated) bowel. Ileal absorption was studied in six dogs with an 80-cm in situ ileal segment via a triple-lumen perfusion technique using an iso-osmolar, ileal-like electrolyte solution alone and containing either glucose 2.5 mM, glutamine 2.5 mM, oleic acid 5 mM, or taurocholate 5 mM. Net absorptive fluxes of each substrate, as well as water and electrolytes, were measured in both the fasted state and after a 400-Kcal mixed meal before and at 2 and 12 weeks after our validated model of complete extrinsic denervation of the jejunoileum. At baseline, there were no differences in absorption of water, electrolytes, or any nutrient postprandially compared with the fasted state. Two weeks after extrinsic denervation, absorption of glucose at both 1 and 2 hours postprandially was decreased compared with absorption during fasting. Glutamine absorption was also decreased at 2 hours postprandially. At 12 weeks after extrinsic denervation, net postprandial absorption of glucose and glutamine returned toward normal and was not different from fasting absorption. No differences were noted in postprandial absorption of oleic acid or taurocholate at any time point. Decreases in absorption of nutrients postprandially after extrinsic denervation (which is necessitated by small bowel transplantation) may play an important role in post-transplant enteric absorptive dysfunction. The previously described postprandial augmentation in net absorption may be a function of enterically isolated gut and does not appear to occur in the in situ ileum.

Canine small bowel motor patterns and contractions are not neurally regulated during enteric nutrient infusion

The aims of this study were to determine the effects of duodenal and jejunoileal nutrient infusions on small intestinal motor patterns and intestinal contractions in neurally intact and neurally isolated small bowel. Fifteen dogs were prepared with duodenal and jejunal infusion and manometry catheters and a diverting jejunal cannula. Ten of the dogs underwent in situ neural isolation of the jejunoileum. A mixed nutrient meal (0.5 kcal/ml) was infused into the duodenum or jejunum at 3 ml/min for 5 h. Control experiments involved infusion of a balanced salt solution. Manometric data collected on-line to a microcomputer were analyzed for direction, distance, and velocity of spread of single pressure waves (SPW) and clustered contractions. Isolated duodenal and jejunoileal nutrient infusions inhibited the fasting motor pattern in neurally intact and neurally isolated small bowel. Motor activity (motility index) increased slightly during nutrient infusion within groups, but there were few differences between groups. Neither neural isolation nor nutrient infusion had a consistent effect on spread of SPW or migration of clustered contractions. Isolated duodenal and jejunoileal nutrient infusions in the dog inhibit fasting motor patterns and increase motor activity slightly but have little effect on characteristics of individual and clustered contractions. Extrinsic innervation to the jejunoileum or intrinsic neural continuity of the jejunum with the duodenum had little effect on single or grouped contractions. Although the changes in motor activity demonstrated in this study appear small, alterations in intestinal transit and absorption may still occur and may be of importance physiologically.