1. Effects of short-chain fatty acids (SCFA) on epithelial proliferation of the intestine were studied in ileally fistulated rats fed on an elemental diet.2. The stimulatory effect of daily doses of acetic, propionic and n-butyric acids (100,20 and 60 mM respectively; pH 6.1) per fistula (3 ml, twice daily) on crypt cell production rate (CCPR) appeared within 2 d and lasted for at least 5 d.3. The daily doses of SCFA for 14 d increased daily CCPR three to four fold. This effect was independent of the presence of gut bacteria.4. Effects of SCFA were dose-dependent and varied among acids (butyrate > propionate > acetate). The effect was independent of low lumen pH.5. In contrast, SCFA inhibited epithelial proliferation of isolated rat caecal tissue in vitro.6. These results suggest that SCFA are physiological lumen trophic factors mediated by a systemic mechanism in vivo.7. It is concluded that SCFA are involved in the trophic effects of gut microbes, ingestion of fermentable fibre, and lumen contents.

We investigated the effects of fructooligosaccharides on the absorption of calcium, magnesium and water from the colon and rectum of rats fed a control diet or the control diet containing 50 g fructooligosaccharides/kg. Chromium-mordanted cellulose was used as an unabsorbable marker to calculate apparent absorption of calcium and magnesium. There was a positive correlation (r = 0.982, P < 0.001 in rats fed the control diet and r = 0.975, P < 0.001 in rats fed the fructooligosaccharides-containing diet) between the amount of chromium and the dry weight of each fecal pellet in the colon and rectum. Ratios of calcium to chromium and magnesium to chromium in fecal pellets in the colon and rectum were calibrated from the Ca:Cr and Mg:Cr ratios of cecal contents. In rats fed the fructooligosaccharides-containing diet, but not in rats fed the control diet, these ratios were correlated with the fractional length of transit along the colon and rectum, indicating linear disappearance of calcium and magnesium during the colorectal passage. Total apparent absorption of calcium and magnesium, predicted from regression equations with the Ca:Cr and Mg:Cr ratios of cecal contents, agreed well with those calculated from the Ca:Cr and Mg:Cr ratios of feces. The consumption of fructooligosaccharides did not affect net water absorption from the colon and rectum. These results indicated that fructooligosaccharides significantly increased calcium and magnesium absorption and that indigestible and fermentable carbohydrate facilitates colorectal absorption of calcium and magnesium.

Two pairs of adult castrated male sheep were given intraruminally 2 g/kg body weight per day of sodium n-butyrate rapidly 10 s at noon or slowly over 20 to 24 h from noon in four trials in which they received only mixed minerals and water ad libitum. Their ruminal papillae were biopsied just before each administration and 24 h after the final administration. Mitotic indices of the epithelial cells were observed. Mitotic indices were lower than .48% before butyrate administration. In sheep rapidly administered butyrate, mitotic indices increased to 1.29%, 2.33%, 2.65%, and 1.84% in 1 day after the first administration in four trials and tended to decline on later days. In sheep slowly administered butyrate, mitotic indices stayed lower than .50% and did not show significant fluctuations. Our data support our hypothesis that an increase in the rate of intraruminal production of volatile fatty acids promotes proliferation of epithelial cells of the organ.