Jejunal brake: inhibition of intestinal transit by fat in the proximal small intestine

Optimal absorption of fat requires adequate time of contact with the absorptive sites of the small intestine. In order to prevent steatorrhea, intestinal transit must be slowed in response to the fat that has emptied into the small intestine. Intestinal transit is known to be inhibited by fat in the ileum via the ileal brake. This response has suggested that the regulation of intestinal transit is a function of the distal small intestine. However, clinical observations suggest that the ileal brake is not the only control mechanism for intestinal transit. In short bowel patients with resection of the ileum, the proportion of fecal fat recovery remained constant even after the fat intake was increased threefold. In these patients, optimal fat absorption based on the slowing of intestinal transit must have been triggered by an inhibitory mechanism located outside of the distal small intestine. To test the hypothesis that fat in the proximal small intestine inhibited intestinal transit, we compared intestinal transit during perfusion of the proximal half of the small intestine with 0 (buffer only), 15, 30, or 60 mM oleate in dogs equipped with duodenal and mid-intestinal fistula. Intestinal transit across a 150-cm test segment (between fistulas) was measured by counting for the recovery of a radioactive marker in the output of the mid-intestinal fistula during the last 30 min of a 90-min perfusion. We found that oleate inhibited intestinal transit in a load-dependent fashion (P < 0.005). Specifically, while the mean cumulative recovery of the transit marker was 95.5% during buffer perfusion, the recovery decreased when 15 mM (64.3%), 30 mM o(54.7%), or 60 mM oleate (38.7%) was perfused into the proximal half of the small intestine. We conclude that fat in the proximal small intestine inhibits intestinal transit as the jejunal brake.