Scintigraphic techniques can measure sequentially gastric emptying, small bowel transit, and colonic transit in humans, and comparable methods for experimental studies in animals would be useful. We developed such a method in dogs and examined the effects of prokinetic drugs on regional transit. Two isotopes were given to fasting dogs. Polystyrene pellets labeled with99mTc were mixed in a can of dog food and 111In- labeled pellets were given in a gelatin capsule coated with a pH-sensitive polymer, designed to dissolve in the distal bowel. Gamma camera images were obtained for up to 24 h. Prokinetic drugs were given by intravenous injection. Duplicate baseline studies showed good agreement in seven dogs. In a second group ( n = 4), intra- and interanimal variabilities were established. Two novel prokinetic drugs (AU-116 and AU-130) accelerated small bowel and colonic transit. A simple noninvasive method for measuring whole gut transit in dogs was developed and validated. Two new prokinetics accelerated small bowel and colonic transit.

To explore mechanisms whereby unabsorbed nutrients in the ileum inhibit the upper gut ("ileal brake"), we perfused the canine ileum or colon and monitored phase 3 in the duodenum. Fasting motility was recorded when the ileum or colon was perfused with 154 mM NaCl, a mixed isotonic nutrient solution (Ensure), or individual nutrients (maltose, casein hydrolysates, or sodium oleate). Blood samples were collected before and during the perfusions. The ileum was also perfused with 154 mM NaCl while peptide YY (PYY) was infused by vein. In both sets of experiments, plasma levels of PYY, neurotensin, and glucagon-like peptide-1 (GLP-1) were measured. Ileal or colonic perfusion of Ensure delayed phase 3 [migrating motor complexes (MMC)] in the duodenum, inhibited ileal motility, and increased plasma levels of PYY and GLP-1. Ileal casein and oleate and colonic casein also delayed the duodenal MMC. The MMC cycle length and plasma levels of PYY were closely correlated. Intravenous PYY prolonged the MMC cycle; an intravenous dose of 100 pmol.kg-1.h-1 of PYY mimicked the effects of ileal Ensure. These results support the hypothesis that PYY, and possibly GLP-1, participate in the ileal brake. This negative feedback loop also affects the distal small bowel. The proximal colon also triggers the feedback inhibition of gut motility (colonic brake).

We have previously described a negative feedback loop that inhibits duodenal motility when nutrients are infused into the ileum and colon. In the present study, we examined the role of extrinsic innervation and plasma levels of peptide YY (PYY) in mediating this phenomenon. We perfused neurally intact ( n = 5 dogs) or extrinsically denervated ( n = 6 dogs) isolated loops of proximal colon with isomolar NaCl or a mixed-nutrient solution at 2 and 6 ml/min for 4 h during fasting or for 2 h beginning 15 min after a meal. Both rates of infusion with NaCl prolonged the cycle length of the duodenal migrating motor complex (MMC) in the group with neurally intact loops but not in the group with extrinsically denervated loops. Nutrient infusions increased the MMC cycle length in both groups. Integrated plasma concentrations of PYY were increased by nutrients but not by NaCl in both groups. These data suggest that increased volumes and unabsorbed nutrients in the proximal colon alter proximal small bowel motility. Volume-induced effects are mediated via extrinsic nerves, whereas nutrient-induced effects may be mediated by humoral factors, such as plasma PYY.

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