Effects of glutathione and of cysteine on intestinal absorption of selenium from selenite.
The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of 75Se-labeled selenite (10 mumol/L) was investigated in rat jejunum. For comparison, the effect of L-cysteine (1 mmol/L) on in vivo absorption of 75Se-labeled selenite was also studied. In the in vitro uptake experiments, only the mucosal surface was exposed to the incubation medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal Se uptake, whereas absorption in vivo was stimulated by GSH. L-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlike L-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of the reaction of selenite with GSH occurring more efficiently under in vivo than in vitro conditions may be a prerequisite for the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from selenite.