GASTROINTESTINAL WATER AND ELECTROLYTES. II. THE EQUILIBRATION OF RADIOPOTASSIUM IN GASTROINTESTINAL CONTENTS AND THE PROPORTION OF EXCHANGEABLE POTASSIUM (Ke) IN THE GASTROINTESTINAL TRACT 1

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Abstract
Intraluminal gastrointestinal K content was measured in rabbits and in human subjects studied postmortem. In rabbits, gut K was referred to the Ke, as determined with K42/43. In human subjects, gut K was referred to predicted Ke values. The total exchangeable K in rabbits averaged 50.7 [plus or minus] 4.0 meq/kg of body weight. Of this, an average of 7.2 [plus or minus] 2.2% was contained in the "total" gastrointestinal tract, with 0.7 [plus or minus] 0.3% in the stomach, 1.2 [plus or minus] 0.4% in the small intestine, and 4.5 [plus or minus] 2.7% in the proximal half of the large intestine. Radiopotassium equilibrium was virtually complete at 40 hours after injection at all levels of the gastrointestinal tract, but not 24 hours after injection. No significant difference in Ke or the quantity of intraluminal gastrointestinal K was found between sexes. Human subjects at postmortem examination had relatively small amounts of intraluminal gastrointestinal K; mean values were 1.0% of the predicted Ke in the "total" gastrointestinal tract, with 0.14% in the stomach, 0.42% in the small bowel, and 0.43% in the proximal half of the large bowel. It is estimated that in the rabbit, about 80% of the total extracellular potassium is located in the gastrointestinal tract. In man, it is estimated that one-third of the total extracellular K is located in the lumen of the gastrointestinal tract postmortem. The relative quantity of intraluminal K in the normal living subject cannot be reliably inferred from these data, however.