Changes of colonic vasoactive intestinal peptide and cholinergic activity in rats with chemical colitis.

The vasoactive intestinal peptide concentration was examined in the colonic wall and portal venous plasma of rats with chemical colitis by radioimmunoassay, and the colonic localization was determined with immunocytochemistry. Colonic acetylcholine esterase activity was also measured, and the response of vasoactive intestinal peptide to acetylcholine administration was determined. Colitis was induced by administration of dextran sulfate for three months. The chemical colitis was histologically similar to active human ulcerative colitis. We observed a significant increase of immunostained neurons and nerve fibers and a significant rise in the colonic wall vasoactive intestinal peptide content in chemical colitis rats, while plasma concentrations of the peptide did not change significantly. Colonic acetylcholine esterase activity was significantly elevated in colitis rats compared with control rats. Systemic administration of acetylcholine significantly increased the colonic and plasma vasoactive intestinal peptide concentrations in colitis rats. These findings demonstrated a positive association between colitis activity and an increase of vasoactive intestinal peptide and suggested that increased vagal tone promoted the peptide's release.