Bidirectional transfer and tissue accumulation of folic acid by rat intestine in vitro.

The transfer and tissue content of 3H-pteroylmonoglutamate (PteGlu) from the mucosal to the serosal side (Jms, TCm) and in the reverse direction (Jsm, TCs) was studied using the everted sac technique. In the entire intestine, except for the colon, 3H-PteGlu was transferred preferentially into the serosal solution. When 3H-PteGlu was applied to the serosal side the final tissue concentration in either jejunal, duodenal, ileal or colonic segments was not significantly different from each other and about two-fold the serosal concentration. Apparently there exists a specific transfer process from the mucosal to the serosal side in the jejunum. The transfer of 3H-PteGlu shows saturation kinetics (S0.5 = 4.9 X 10(-5) mol/l). At low concentration (2 nmol/l) 3H-PteGlu was accumulated within the mucosal epithelium (tissue/mucosal fluid ratio = 3.8). Transfer and accumulation in the mucosal tissue of 3H-PteGlu apparently need high activation energy as indicated by the temperature dependency of these processes. Finally, transfer and accumulation in the tissue of 3H-PteGlu could be inhibited by salazosulfapyridine and phenobarbital.