Jejunal Uptake of Tritiated Folic Acid in the Rat Studied by in vivo Perfusion

Abstract

The jejunal uptake of tritiated folie acid was measured in male Wistar rats by in vivo perfusion. The uptake of 3H-folic acid was linear relative to concentra tions between 4 nM and l /UM,but between concentrations of l UM and 4.6 MM,uptake was similar, suggesting a saturable uptake process. A double reciprocal plot ( Lineweaver- Burk) yielded a fC„, value of 1.57 /IM with a V„„ value of 0.654 itmoles/cm/hour. Ex posure of the lumen to 11 /UMmethotrexate, an inhibitor of dihydrofolate reducA­ase, prior to and during perfusion of 1.1 /AM 3H-folic acid resulted in a significant decrease of jejunal dihydrofolate reducA­ase (folie acid reducA­ase, EC 1.5.1.3) with no change in the jejunal uptake of H-folic acid. There was no observable difference in jejunal dihy drofolate reducA­ase nor of the uptake of H-folic acid among rats fed normal diet, normal diet plus ethanol, a protein-deficient diet, or a protein-deficient diet plus ethanol. These studies suggest that the initial uptake of 3H-folic acid by the jejunal mucosa is rate limited between concentrations of 1 and 4.6 /IM, does not require metabolic reduc tion, and is not affected by protein deficiency or elhanol. J. Nulr. 104: 1674-1680, 1974.