Dose-dependent stimulatory and inhibitory effects of luminal and serosal n-butyric acid on epithelial cell proliferation of pig distal colonic mucosa.

Large bowel bacteria convert various carbohydrates into short-chain fatty acids (SCFA). SCFA stimulate epithelial cell proliferation of the large intestine in vivo and inhibit that of various cells in vitro. Supposing that too high concentration of SCFA on the serosal side is responsible for their inhibitory effect in vitro, we studied effects of luminal and serosal n-butyric acid (0, 0.1, 1, or 10 mmol/L, adjusted to neutral pH) on the epithelial cell proliferation rate of pig colonic mucosa in organ culture taking crypt cell production rate (CCPR) as the measure of proliferative activity. With 0 or 0.1 mmol/L n-butyric acid on the serosal side, luminal n-butyric acid increased CCPR at 1.0 mmol/L, and decreased CCPR at 10 mmol/L when compared to the luminal 0 mmol/L control. With 1.0 or 10 mmol/L serosal n-butyric acid, luminal n-butyric acid depressed CCPR dose-dependently. The above results indicated that n-butyric acid stimulated colonic epithelial cell proliferation at low concentration and inhibit it at high concentration with interaction effect to enhance the inhibitory action. The stimulatory effect of a low dose of serosal n-butyric acid may be responsible for the distant trophic effect of SCFA.