Colonic vasoactive intestinal polypeptide in ulcerative colitis.

Vasoactive intestinal polypeptide (VIP) is a 28 amino acid peptide which is localised in both the central and peripheral nervous system. In the human colon VIP is found in all layers and the highest concentrations have been found in the myenteric plexus. It is known that VIP has various effects on intestinal functions: i) it is a potent stimulant of mucosal water and electrolyte secretion; ii) it is involved in the peristaltic reflex; and iii) plays an inhibitory role on immune cell function. Based on these biological effects it has been hypothesized that the intestinal mucosal immune system and inflammation may be influenced by alterations in the tissue concentrations of VIP. Some authors have demonstrated no changes in the VIP colonic content of patients with ulcerative colitis, whereas others have demonstrated a reduction. Our results, using specific radioimmunoassay, showed that there is a significant decrease of VIP in both rectal and colonic mucosa of patients with ulcerative colitis as compared to controls. The VIP decrease is selective since substance P and calcitonin gene-related peptide were unchanged in the mucosal tissue of ulcerative colitis patients and furthermore the VIP alteration is correlated to the degree of mucosal inflammation. These findings suggest that the reduction of VIP mucosal content, even if it represents a non-specific event, could influence local inflammatory response and the activity of the disease.