The role of liver passage for conversion of pteroylmonoglutamate and pteroyltriglutamate to active folate coenzyme.

In an attempt to clarify the possible site of conversion of folates to active methylated coenzyme forms mono- and triglutamate was injected rapidly into the portal vein of dogs. Samples of blood were removed at various intervals from catheters placed in the portal vein, the hepatic vein and the femoral artery for assay carried out both with L. casei, S. Faecalis and liquid scintillating counting. Unreduced monoglutamates were extracted in the liver, immediately converted to methyltetrahydrofolate and released again to plasma from which it was slowly taken up by peripheral tissue. Reduced folates were refused by the liver. Triglutamates were extracted exclusively in the systemic circulation, converted to unreduced monoglutamate later to be reduced in the liver. No tissue displacement of folate was demonstrated. Only small amounts of monoglutamates, mainly reduced forms, were lost in the urine during the experiments. The kinetics of unreduced monoglutamate suggest a one compartment system, while the kinetics of methyltetrahydrofolate and triglutamate may implicate a two compartment system.