Uptake and reduction of radioactive folate by everted sacs of rat small intestine.

Abstract

Uptake of pteroylglutamie acid ([2‐14C]PteGlu) by everted sacs of rat small intestine was studied. Under conditions of zero initial concentration gradient, a net transport of PteGlu from the mucosal to the serosal side was found at initial concentrations not exceeding 7 μM.Using a simplified chromatographic procedure for estimation of reduced folates it was found that part of the transported PteGlu was converted to reduced forms, tentatively identified as tetrahydropteroylglutamic acid (H4PteGlu) and its methyl and formyl derivatives. PteGlu was reduced throughout the small intestine. The reduction was time and concentration dependent with an apparent Km of 1.55 μM.Low concentrations of methotrexate (23 μM) inhibited the reduction of PteGlu but did not affect its transport; at a much higher concentration (3 μM) methotrexate decreased the accumulation of folates in the tissue without significantly affecting the vitamin concentration in the serosal solution.