Small intestinal mucins are secreted in proportion to the settling volume in water of dietary indigestible components in rats.

The aim of this study was to clarify the effect of dietary indigestible components on small intestinal mucin secretion. We prepared polystyrene foam (PSF) with different expansion ratios (PSF-30, -60 and -90) in which powders had different settling volumes in water (SV). Rats were fed a purified diet containing 0, 10, 30, or 90 g of PSF-60/kg for 10 d. After 8 h of food deprivation, rats were refed 3 g of their respective diets within 90 min. Small intestinal mucin fractions were prepared, and periodic acid/Schiff-reactive substances and O-linked oligosaccharide chains were determined as mucin markers. Feeding of PSF-60 increased the small intestinal mucin secretion dose dependently (control vs. 30 or 60 g of PSF-60/kg, P < 0.05). When rats were fed either purified diet or diets containing PSF-30, 60, or 90 at 10 g/kg for 7 d, small intestinal mucins were greatly affected by the SV of the respective PSF tested. Rats fed the diet containing PSF-90 with the highest SV had the highest amount of mucins (vs. control, P < 0.05). In some natural dietary fibers, the small intestinal mucins and SV were correlated (r = 0.967, P = 0.002). Finally, rats were fed a purified diet or that diet containing 50 g of PSF-60/kg for 7 d. Then, each dietary group was further divided into 2 groups. After 8 h of food deprivation, rats were refed 3 g of purified or PSF diet. Greater mucins in the small intestine were manifest only in rats previously fed the PSF diet whether they were refed purified or PSF diet (control vs. PSF, P < 0.05). These results suggest that the small intestinal mucins are secreted in proportion to the SV of dietary indigestible components, and chronic ingestion of indigestible components is required for the appearance of enhanced mucin secretion.