Relationship between small bowel transit time and absorption of a solid meal. Influence of metoclopramide, magnesium sulfate, and lactulose.

The times taken for a radiolabeled solid meal to empty from the stomach and terminal ileum and the absorption of the components of that meal were measured in 14 patients with terminal ileostomies under control conditions and after administration of either lactulose (40 g) or metoclopramide (20 mg tds), or magnesium sulfate (0.1 g/kg body weight). Absorption of each of the components of the meal was determined by chemical analysis of the ileostomy effluent. The radioisotope proved an excellent marker for the delivery of fat, protein, and carbohydrate residues. All three agents significantly reduced the time taken for the meal to empty from the ileum. This was associated with significant reductions in the absorption of fat, carbohydrate, protein, water, and electrolytes in the case of lactulose and magnesium sulfate. Although metoclopramide reduced transit time to the same degree as the other agents, its effect on absorption of fat, fluid, and electrolytes was much less, and absorption of protein and carbohydrate was unaffected. We therefore conclude that, although agents that accelerate postprandial transit of a meal may diminish absorption of the component of that meal in the small bowel, the extent to which this occurs cannot be predicted by a knowledge of transit kinetics alone and depends on the means by which transit is altered. The action of lactulose on the small intestine causes fluid and fat losses, sufficient to result in diarrhea and steatorrhea in a normal subject.