Proinflammatory effects of local abdominal irradiation on rat gastrointestinal tract.

Although the role of inflammatory processes in the genesis of late changes in the gastrointestinal tract following exposure to ionizing irradiation has been extensively studied, few studies have concentrated on the presence of an acute inflammatory response in the period immediately following radiation. We therefore examined, in rats, whether the local application of 10 Gy cobalt-60 irradiation to the abdomen led to changes in the gut within the first 24 hr that were consistent with an acute inflammatory response. In stomach, small intestine, and colon, local irradiation led to a significant increase in the accumulation of plasma within the tissue by 4-8 hr following irradiation. This increase in tissue plasma volume, indicative of an increased microvascular permeability, was then sustained until the end of the 24-hr assessment period in all tissues examined. Concurrent with this was a consistent transient increase in tissue red blood cell volume, suggestive of vasodilation. Of particular note, a significant increase in the number of mucosal neutrophils was also observed between 2 and 12 hr following irradiation. This elevation in mucosal neutrophils was particularly marked in the pericryptal or deep mucosal regions of small intestine and colon and consistently preceded the vasodilation and enhanced permeability. Furthermore these pathophysiological alterations occurred at a time when histological changes in the mucosa consistent with an impaired mucosal microcirculation (ie, edema of the lamina propria and subepithelial bleb formation) were present. These results support the hypothesis that an inflammatory response occurs in the gut during the first 24 hr following abdominal irradiation. Such changes may then further exacerbate the damage initiated by the ionizing radiation.