Retention of${}^{35}{\rm Na}{}_{2}{\rm SO}_{4}$,45 CaCl2, and$1\text{-}{}^{14}{\rm C}\text{-glycine}$ in the stomach following intragastric administration has been studied in irradiated mice and rats. Simultaneously, blood levels of these substances have been determined. Following whole-body x-irradiation (600 R, exposure rate 17.7 R/min, HVL 1.03 mm Cu), retention of gastric contents takes place in mice and rats, yet its course is not identical in both species. As soon as 30 minutes postirradiation, high retention of gastric contents is observed in both mice and rats, which must be attributed to the influence of ionizing radiation. In mice, on the first day following irradiation the evacuation of gastric contents returns to normal, but another retention maximum occurs about 2 to 3 days postirradiation. Six days following irradiation, more rapid evacuation of gastric contents is found in irradiated mice than in the control animals. In rats, delayed evacuation of the stomach is found at all the time intervals investigated (up to the sixth day), the highest values being found during the first days (up to the third day). Blood levels of the substances vary inversely with the gastric levels. This demonstrates the importance of retention as a factor which influences the rate of absorption of all substances in irradiated animals.

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