Gastrointestinal adaptation to enhanced small intestinal lipid exposure.

Studies were performed on 20 male adult rats to investigate the effects of chronic intermittent infusion of lipid and physiological emulsifier into the distal small intestine on stomach to caecum transit time (SCTT) of the head of a test meal. SCTT was measured using environmental hydrogen analysis. Ileal lipid infusion normally delays gastric emptying and small intestinal transit (p < 0.001), but chronic intermittent infusion of lipid, given three times a week gradually reduced the delay in transit time until by four weeks it was no longer than control values. The lipid induced delay did not return during the four weeks after the chronic infusion had finished. Intermittent infusion of physiological emulsifier into the distal small intestine for four weeks did not change the control SCTT or the acute response to an ileal lipid infusion. SCTT of the head of the meal did not change in the four weeks after the physiological emulsifier infusion had stopped. In conclusion these results show that infusing rats intermittently with lipid for four weeks results in desensitisation of the mechanisms by which distal small intestinal lipid regulate SCTT of the head of a meal. This adaptation is not reversed within four weeks of withdrawal of the lipid infusion. These results emphasise the importance of assessing recent dietary history when assessing gastric emptying and small bowel transit times.