Squamous metaplasia in the healing of chronic colonic ulcers of the rat.

Chronic ulcers of the rat colon were produced by a administering a 3 per cent. hydrogen peroxide enema. Twenty-three per cent. of the animals with chronic ulcers had areas of squamous metaplasia at the wound margins which in some cases covered the defect. Electron microscopy revealed some areas similar to epidermis with the four characteristic cell layers. The cells demonstrated many filaments, membrane-coated granules, keratohyalin granules and keratin. The cells were linked by complex of cytoplasmic bridges and frequent desmosomes. Basal cells often displayed large irregular nuclei with double nucleoli. Other areas demonstrated a grossly irregular surface with marked cellular pleomorphism and defects in the basement lamina. The incidence of squamous metaplasia and squamous-cell carcinoma in the colon of man is discussed. The ultrastructural characteristics of squamous metaplasia in the trachea and bronchi is recorded and compared with those of the colon. It is suggested that as neoplasia has been observed to follow experimental metaplastic lesions in the bronchus, a similar ocurrence could take place in the colon as the squamous cells exhibited similar characteristics.