Experimental production of diffuse colitis in rats.

Diffuse, topical application of dilute acetic acid to the serosal surface of rat colon, or standardized intraluminal (per rectum) instillation induced a reproducible, diffuse colitis in a dose-response manner. These lesions were reproduced with 100% reliability and were evaluated up to 60 days when healing occurred. Histopathological features of this chemically induced colitis were diffuse ulceration of the distal colon, occurrence of pseudopolyp-like structures, alterations in crypt depth and mucus secretion, and a transmural, nonspecific inflammatory response.