Studies on changes of colonic mucosal PGE2 levels and tissue localization in experimental colitis

Experimental ulcerative colitis was produced in rats and the changes of PGE2 levels in the colonic mucosa and the tissue localization of PGE2 were studied immunohistochemically during the process of onset and healing of the experimental lesions. Compared with that in controls, PGE2 levels in colonic mucosa were not significantly higher in the early stage of inflammation, but rose gradually with exacerbation of inflammation, and after reaching peak values at the peak stage of development of colitis, decreased as signs of inflammation receded. Immunohistochemical study of the normal rat colon showed that PGE2 was uniformly positive in the muscularis mucosa and in the tunica propria muscularis adjacent to the submucosal layer. Furthermore, as the inflammation progressed infiltrating inflammatory cells also became positive, especially macrophages. These changes decreased along with regeneration of the epithelium and resolution of the inflammation. Glandular epithelial cells did not show positivity. These results made it clear that the PGE2 level in colonic mucosa is an useful index of the activity of colitis and that changes in PGE2 levels are associated with infiltration by inflammatory cells, principally macrophages, of the interstitium. The results also suggested the possibility that the muscularis mucosa plays a role in the colonic mucosal protective system.