The influence of lumenal pH on the severity of acute radiation enteritis

The severity of acute radiation injury to small bowel mucosa was studied as a function of lumenal pH at the time of irradiation. Rats were anaesthetized and 15 cm of mid small bowel was exteriorized with the rest of the animal and intestine shielded in a lead box. The target intestine was segmented into three portions, each of which was filled with Tris buffer, adjusted to pH 5, 7 and 9 respectively. Twenty minutes later the exteriorized bowel was given 1100 cGy X-irradiation. Rats were sacrificed 4, 5 and 6 days later and the intestine histologically assessed for injury. The indices of injury were surviving crypt numbers, mucosal height and mucus-containing goblet cells. To verify that pH was the critical variable an identical study was done employing three buffers chemically different from Tris: MES (pH 5.5), ADA (pH 7), and CAPSO (pH 9). These animals were sacrificed 5 days postirradiation. For all three parameters, and on each day postirradiation, the pH 9 segment showed less damage than did the segments with lumenal pH 7 or 5. We conclude that lumenal pH at the time of irradiation plays a significant role in the severity of acute mucosal injury. Alkaline pH is relatively protective.