Ultrastructural modifications of intestinal and colonic mucosa induced by free or bound bile acids

There is substantial evidence that bile acids may enhance the colon tumorigenesis induced by chemical carcinogens and that agents stimulating increased bile acid excretion may show similar promoting or enhancing activity. To test the premise that these agents might modify topographical ultrastructure of the small intestine and colon in the absence of carcinogens, rats were fed for 6 weeks on chemically defined diets containing 2% levels of three commercial bile acid sequestrants or 15% levels of wheat brain, cellulose, pectin, or alfalfa. Major qualitative and quantitative deviations from normal morphology were observed with each of the three sequestrants. Similar but less dramatic modifications occurred with diets containing alfalfa or pectin, both of which either "bind" bile acids in vitro or result in increased bile acid excretion. Bran and cellulose which neither "bind" bile acids nor increase their fecal excretion, were without significant effects on intestinal or colonic morphology. The morphological deviations observed with bile acid sequestrants were shown to be a direct response to free or bound bile acids by comparing the morphological modifications resulting from daily intracolonic infusions of free bile acids, sequestrant-bound bile acids, or the sequestrant alone.