Organic anions induce colonic secretion

Experiments were conducted by instilling test solutions into the cleaned colon of anesthetized rats. Isotonic test solutions at an acid (2.9) or neutral (7.0) pH and containing acetic acid or acetate ions were used. At the lower pH, acetic acid was absorbed and water was secreted. At the higher pH, acetate ions were less well absorbed and the colon absorbed fluid. The secretory effect could not be reproduced by hydrochloric acid solutions at pH 2.9. Fluid secretion induced by acetic acid was associated with discharge of mucus from goblet cells. The interference of colonic absorption by acetic acid might be important in some diarrheal diseases.