Effect of 4'-oxythiamine on thiamin transport and phosphorylation by everted jejunal sacs, and on thiamin uptake by rat isolated enterocytes.

Two preparations were used for the present investigation. Rat everted jejunal sacs were incubated at 37 degrees C for 1 h in Krebs-Henseleit buffer, pH 7.4, containing 0.2 microM [thiazole-2-14C] -thiamin, with or without 2 microM 4'-oxythiamine. Suspensions of rat isolated enterocytes were incubated at 37 degrees C for 15 min in Ringer-Krebs, pH 7.4, containing 10 mM d-glucose and 0.125 microM [thiazole-2-14C] -thiamin, with or without 1.25 or 12.50 microM 4'-oxythiamine. Radiometric methods were used for the determination of: labeled thiamin net transport, free and phosphorylated thiamin content in the sac walls, total thiamin content in the isolated enterocytes. 4'-oxythiamine, at a molecular ratio with thiamin of 10:1, did not modify labeled thiamin net transport and accumulation by everted jejunal sacs, but caused a slight, statistically insignificant, decrease of labeled phosphorylated thiamin content of the sac walls. 4'-oxythiamine, at a molecular ratio of 10:1 or 100:1, did not inhibit labeled thiamin uptake by isolated enterocytes. Therefore, 4'-oxythiamine, which is known to be unable to inhibit thiamin enzymatic phosphorylation, did not affect thiamin intestinal transport both by everted intestinal sacs and isolated enterocytes. The present results can be interpreted as a further evidence that intracellular thiamin phosphorylation is an important step in thiamin intestinal transport.