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

Abstract

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.

Gut feedback mechanisms and food intake: a physiological approach to slow carbohydrate bioavailability

“…The ileal brake is a term describing a specific status of gastrointestinal activity (such as slow contraction, secretion inhibition) resulting from undigested nutrients reaching the ileum under normal physiological conditions, and it is defined as "the primary inhibitory feedback mechanism to control transit of a meal through the gastrointestinal tract in order to optimize nutrient digestion and absorption". 155,156 Thus, the ileal brake represents the negative feedback system in the digestive system to tune the assimilation of nutrients. Actually, ileal brake is just one type of brake mechanism in the gastrointestinal tract in response to unabsorbed nutrients.…”

The ileal brake: A fifteen-year progress report

“…The recently characterized colonic brake [25] is thought to be mediated by PYY [17••], with peptone being the most potent trigger. The ileocecal junction may play a significant role in orocecal transit time as evidenced by accelerated transit following resection [26].…”

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

“…12 In our experiments, the perfusion of the ileum with liquid test material at a rate of 1.7 ml/min for 30 min would certainly have resulted in the overfl ow of some liquids into the colon. We found a reduction and a delay in the onset of the motor inhibitory effect of the intraileal glucose in dogs after a total colectomy.…”