Experimental studies on the pathogenesis of the chronic radiation ulcer of the large bowel in rats.

Following local irradiation of a 24 mm segment of the large bowel with 23 Gy, 90% of Wistar rats developed a chronic radiation ulcer leading to progressive large bowel obstruction within 8 weeks. The incidence and latency of the chronic radiation damage was markedly altered by local treatments after irradiation, especially those which modified the amount and texture of the feces. The results of these studies suggest that the primary radiation damage to the large bowel is to the microvasculature of the mucosal and submucosal stroma leading to progressive mucosal atrophy which thus becomes very vulnerable. The chronic radiation ulcer and the hypertrophic, cystic mucosa (which is the result of hyperregeneration of subclinical ulcers) are secondary to the interaction of the primary radiation damage to the vascular-connective tissue of the intestinal wall with mechanical and infectious damage to the chronically atrophic mucosa.