Rates of insorption of sodium and potassium from upper small bowel of rats

¹ Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Rates of insorption of radiosodium and radiopotassium from the unobstructed small bowel of rats were determined and compared with those obtained by others in healthy humans. Insorption of the isotopes under study was estimated by integration of their rates of appearance in the blood after placement in the small bowel and their rates of disappearance from blood after injection into the circulation. The rates of disappearance from arterial blood were determined during separate tests. They followed an exponential pattern similar though not identical with that reported from other species by other investigators. Radiosodium was insorbed more rapidly than radiopotassium. Mean values indicated that 50% of administered radiosodium was insorbed within 6–7 min, whereas 26–27 min were required for insorption of 50% of the radiopotassium. The rate constant during insorption of the first 76% of the Na²² was 10.8% per min and that for insorption of 58% of the K⁴² was 2.7% per min.