Dose-time-dependent histological changes following irradiation of the small intestine of rats

The distal ileum of 48 male Sprague-Dawley rats was exteriorized and irradiated either with low dosis (9-12 Gy, N = 18 rats), moderate dosis (15-18 Gy, N = 18 rats) or high dosis (21-24 Gy, N = 12 rats). A shielded segment of the ileum in the same animals as well as the sham-irradiated exteriorized ileum of 10 rats served as controls. The animals were allowed to survive for 3, 10, or 30 days. A total of 16 histologic parameters were found to be relevant for this study. Cell necrosis, loss of goblet cells, crypt abscesses, structural changes of the crypts, loss of Paneth cells, decreased number of mitoses, appearance of clear basal cells, loss of margination of lymphocytes, increased colagen in the submucosa, muscularis propria and subserosa, ectopic mucosal glands, as well as mucosal ulcerations, were found to be dose-time-dependent irradiation changes. Racket-shaped superficial epithelial cells, capillary congestion, and an increased number of round cells in the lamina propria mucosa were found to be time-dependent histological parameters. Preparations from the shielded ileum or from the sham-irradiated control animals showed normal histology. This study appears to be the first in which the systematic analysis of several postirradiation histologic changes have been found to be dose- and/or time-dependent. The knowledge that some radiation changes are dose-time-depeendent, whereas others are exclusively time-dependent, may open new vistas on the study of postradiation enteritis in the rat.