Effect of organic acid absorption on bicarbonate transport in rat colon

The absorption of organic anions and the influence of these anions on the movement of HCO3- were studied in vivo in rat colon using a perfusion technique. The absorption of short chain fatty acids (SCFA's) such as acetate, propionate, and butyrate was much greater than that of succinate or lactate. With increasing initial concentration of SCFA up to 100 mmol . 1-1, SCFA absorption increased linearly in correspondence with HCO3- appearance. Final pCO2 level of the perfusion solution with SCFA was the same as the plasma level. Among the SCFA's, no significant differences in absorption or their effects on HCO3- appearance were observed. The presence of Na+ stimulated SCFA absorption, and the maximum value was obtained at more than 100 mmol . 1-1 of Na+. These results suggest that a specific system for HCO3- secretion activated by SCFA exists in the colon, and that this system may control the intraluminal pH by the alkalization of intestinal contents.