X-irradiation inhibits gastrointestinal absorption of nutrients by damaging the intestinal mucosal cells which actively transport these chemicals. The results of the present study demonstrate that sublethal doses of X-irradiation delay the passive gastrointestinal absorption of an acidic drug, sulfadiazine, and a basic drug, quinine, in mice. This effect is detectable 2 hr after radiation exposure and is most pronounced in the first 3 postirradiation days. Both the magnitude and the duration of the effect are related to the radiation dose (25-300 R in mice and 200-800 R in rats). The effect was not demonstratable when sulfadiazine was given by intraperitoneal or intraduodenal rather than by intragastric administration after which more of the drug was retained in the stomachs of rats irradiated 21 hr earlier. Head irradiation, which is known to delay gastric emptying, lowered blood levels of sulfadiazine after gastric administration, and shielding partially protected against this delayed drug absorption. This effect was most pronounced in whole body irradiated rats. Thus, delayed gastric emptying is the major cause of inhibited gastrointestinal drug absorption in the first 3 days after irradiation of mice and rats.

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