BACKGROUND Inflammatory bowel disease (IBD) is associated with changes in colonic motility which may contribute to the pain and diarrhoea associated with exacerbations of this disease. These changes may be mediated by prostaglandins which are increased in this condition. Increased expression of the inducible isoform of cyclo-oxygenase (COX-2) has been found in active IBD although its cellular distribution remains uncertain.

AIMS To evaluate the cellular distribution of COX-2 in active IBD.

PATIENTS AND METHODS Using reverse transcription-polymerase chain reaction, in situ hybridisation, and immunohistochemistry, COX-2 expression was evaluated in 12 colectomy specimens from patients with active ulcerative colitis (UC), and six specimens from patients with Crohn's colitis that had failed medical therapy. Histologically normal colon was obtained from 12 patients having resection for colorectal neoplasia and evaluated as above, acting as control specimens.

RESULTS All specimens expressed COX-2 mRNA, with some 6–8-fold increase in inflamed tissues on densitometric analysis (both UC and Crohn's) compared with controls. In situ hybridisation localised this mRNA to myenteric neural cells, surrounding smooth muscle cells, and inflammatory cells of the lamina propria in the IBD specimens, with some weaker labelling seen in the epithelium. No COX-2 labelling was seen in normal tissues. Immunohistochemistry confirmed these sites of COX-2 expression in all inflamed specimens, with absence of immunoreactivity in control tissues.

CONCLUSIONS These findings provide the first evidence of COX-2 expression in neural cells of the myenteric plexus in active IBD which, via increased prostaglandin synthesis at this site, may contribute to the dysmotilty seen in this condition.