ABSORPTION OF FOLIC ACID FROM THE SMALL INTESTINE OF THE RAT

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Abstract
The absorption of folic acid from segments of the small intestine of the rat has been measured in situ with tritium-labelled folic acid. The fraction absorbed was independent of concentration below 10−6 m but was depressed to half at 4 × 10−5 m. Direct measurements of fluxes showed that the mucosal → serosal flux was about 14 times the serosal → mucosal flux, and therefore that uptake of folic acid is an active process. In the ileum but not in the duodeno-jejunum, absorption was depressed by the presence of electrolyte. There was little difference in absorptive capacity between jejunum and ileum nor was there any significant change in animals suffering from a dietary deficiency of folic acid.