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Intraluminal perfusion of the human small intestine has not been used extensively to study comparative bioavailability of vitamins. In this study a triple lumen tube with a 30-cm study segment was used to measure absorption of water-soluble vitamins from the human proximal jejunum. Fifteen normal subjects served as their own controls to quantitate absorption of folic acid and vitamin C from an orange juice solution and from a solution of synthetic vitamins. Despite a predictably greater water absorption from the glucose containing orange juice solution, the absorption of the two water-soluble vitamins did not differ significantly from the two solutions. Natural and synthetic ascorbate and folate were avidly absorbed in the first 30 cm of jejunum and with the exception of synthetic folate correlated positively with water absorption. This method, previously applied to the absorption of sugars, amino acids, and electrolytes, can be reliably applied to the study of comparative bioavailability of nutrients from food sources. The advantages of triple lumen perfusion over previous methods are: 1) it overcomes the necessity for urine collections in metabolic studies, 2) it can be used to study sites and mechanism of absorption, and 3) it is a direct measurement of absorption capacity.

Long term use of the drug diphenylhydantoin (DPH) has been associated with biochemical evidence of folic acid deficiency and rarely with megaloblastic anemia. The mechanism of this nutritional deficiency is uncertain but is thought to result from DPH-induced alteration in the intestinal absorption of conjugated and/or free dietary folate. The effect of DPH on the intestinal absorption of free folates from a food source has heretofore not been reported. In this study triple lumen tube perfusion of the human jejunum was used to quantitate folate absorption from a control solution of orange juice and from an identical solution containing DPH. The results in eleven volunteers serving as their own controls indicate no effectof DPH at a concentration of 20 microgram/ml on folate absorption from this food source. The predominant form of folate in orange juice as determined by differential microbiologic assay is N-5-methyltetrahydrofolate. DPH does not appear to interfere with the absorption of free food folate which is both methylated and reduced.

Previous investigations have suggested that there are high potassium losses during heavy physical activities in hot climates. In order to determine if high levels of potassium losses could be offset by potassium loading, this study was conducted with five long-distance track runners who had trained in hot and humid environments. The liquid supplements containing 4.3, 98.0, and 0.0 mEq/liter of potassium were given 1 to 2 hr before physical activity. The daily diet contained 2.6 g of potassium. A sodium and potassium balance study was conducted in which stool, urine, and dermal losses were measured. In order to determine if there was a change in the distribution of body potassium during physical exercise, seven subjects total body potassium was estimated before and after exercise. This measurement was performed by counting 40K in a whole body counter. Although the subjects with potassium supplementation and higher urinary sodium and potassium losses, the 98 mEq/liter of potassium supplement resulted in a positive potassium balance. The subjects' potassium requirements exceeded the National Research Council suggested dietary intake. The total body potassium measurements indicated that the counting efficiency of 40K increases significantly immediately after the period of vigorous exercise.