An electron microscopical study of chronic ulcers of the colon in rats.

Chronic colonic ulcers in the rat were produced by the administration of a hydrogen peroxide enema. Lesions of up to 10 months' duration were obtained by this method and a selection was examined ultrastructurally. It was hoped that the study would reveal causes for the chronicity of the lesions. From previous work it appeared that there was no failure of epithelial migration from the edge of the wound. The majority of cells at the ulcer margins demonstrated features of regeneration similar to those seen in other tissues, and that there were no specific changes concomitant with chronic ulceration. The majority of epithelial cells at the ulcer edge showed features of differentiation which indicated that there was no obvious fault in this process so essential to the basic requirements of tissue repair. It is possible that chronicity is produced by a failure of the epithelio-mesenchymal interaction mechanisms which, potentiated by an ischaemia resulting from submucosal vascular damage, results in the consequential death of migrating epithelial cells. This hypothesis is supported by the appearance of a squamous metaplasia in the healing lesions, a process which is commonly attributed to a chronic inflammatory response which may be induced by a relative vascular insufficiency.