Thiamin transport by rat small intestine "in vitro": influence of endogenous thiamin content of jejunal tissue.

The relationship between thiamin intestinal transport and phosphorylation in vitro was investigated using everted jejunal sacs from normal rats, rats affected with dietary thiamin deficiency at different degrees and relative pair-fed controls; recovered rats, i.e. severely thiamin-deficient animals, 6 hours after the intravenous injection of 1 mg of thiamin chloride/100 g body weight. The sacs were incubated at 37 degrees for 30 min with 0.2 microM 14C-labeled thiamin. During incubation, the endogenous phosphorylated thiamin undergoes a dephosphorylation, which is lowest in thiamin deficient rats. The jejunal sacs from all experimental groups take up and phosphorylate labeled thiamin: the rate is inversely proportional to the endogenous cellular content of phosphorylated thiamin. The net transport of labeled thiamin is enhanced in thiamin-deficient rats. The labeled thiamin net transport after incubation is linearly related to the labeled phosphorylated thiamin content of intestinal tissue. Thiamin repletion of severely thiamin-deficient rats restore the normal levels of endogenous free and phosphorylated thiamin in the intestinal within 6 hours. In addition after incubation, the labeled phosphorylated thiamin content reverts to the levels of the control, while thiamin net transport remains high.