Contractions in vitro of small intestinal segments were studied at varying times following exposure of rats to whole-body x-irradiation. Jejunal contractions were measured 20 to 40 minutes, 4 to 6 hours, 1, 2, 3, 5, 7, 11, and 30 days following 25, 100, and 700 R, as well as during the first 3 days following 1500 R. Duodenum and ileum were studied 2 and 3 days following 1500 R. Sham-irradiated rats served as controls. The irregular contraction pattern characteristic of jejunal segments from nonirradiated rats was changed to a more regular pattern 2 and 3 days after 1500, 700, and 100 R; in addition, exposures with 1500 and 700 R increased contraction amplitude. Two and three days following 1500 R, duodenal, but not ileal segments, showed a significant increase in regularity. Furthermore, the gradient of contraction frequency (duodenum > jejunum > ileum) was maintained, but the gradient of contraction regularity (ileum > jejunum > duodenum) was abolished. Changes in small intestinal motor function following whole-body radiation may significantly contribute to the pathophysiology of intestinal radiation injury.

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