Effect of dietary fiber on intestinal mucosal sodium-potassium-activated ATPase

The effect of dietary fiber on rat intestinal weight, intestinal mucosal Na-K-ATPase, and alkaline phosphatase, and on fecal excretion of water and cations was studied. Rats were fed, for 28 weeks, diets containing 0% (elemental), 5%, or 28% fiber. The fiber-free diet was associated with atrophy, and the high-fiber diet with hypertrophy of the large intestine (79 and 155%, respectively of weights in rats fed the 5% fiber diet). Increased levels of alkaline phosphatase were found in the small intestine of rats fed the elemental diet (200% of levels in rats fed the 5% fiber diet), an effect which appears to confirm the finding observed previously of hypertrophy of enterocyte microvilli in animals fed the elemental diet. Rats fed the high-fiber diet had increased levels of mucosal Na-K-ATPase in the ileum, cecum, and colon (220% of total cecal activity in rats fed the 5% fiber diet). The high-fiber diet was also associated with increased fecal excretion of water, sodium, and potassium (178, 620, and 150%, respectively of levels in rats fed the 5% fiber diet). This effect probably reflects intraluminal trapping of water and cations by fiber with a compensatory rise in mucosal Na-K-ATPase.