EVALUATION IN RATS OF THE DOSE-RESPONSE RELATIONSHIP AMONG COLONIC MUCOSAL GROWTH, COLONIC FERMENTATION, AND DIETARY FIBER

The dose-response relationship among dietary fiber, colonic fermentati on, fecal weight, and mucosal growth were evaluated in this study. The morphometric parameter of total mucosal volume was used to assess die t-induced differences in colonic mucosal growth. Dietary fibers with a wide range of fermentability and that have previously been shown to i nhibit the development of colonic neoplasia in rats were used. Sprague -Dawley rats were fed Purina Rodent Chow, AIN-76a fiber-free diet, or an AIN-76a diet supplemented with three different dietary fibers, (cel lulose, guar gum, or wheat bran) at 2, 5, 10, or 15% of the diet. Diet s were fed for 28 days. Total colonic mucosal volume was determined us ing stereologic principles and computerized image analysis; 48-hr feca l weight was measured; and the concentration of short-chain fatty acid s (SCFA) in colonic contents was determined at study termination. Each type of fiber induced a dose-dependent increase in total mucosal volu me of the colon and fecal weight. Mucosal volume and fecal weight were closely correlated (R(2) > 0.95). Total mucosal volume was not correl ated with the concentration of total SCFA or butyrate in the colon. Th ese results indicate that diet-induced change in colonic mucosal growt h, as measured by total mucosal volume, is positively correlated with fecal weight and not related to alterations in colonic fermentation. E nhanced colonic mucosal growth occurs in rats fed dietary fibers that have previously been shown to inhibit the development of genotoxin-ind uced colonic neoplasia in rats.