The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of Se-75 from Se-75-labeled selenite (conc. 10-mu-mol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term uptake technique. L-Cysteine (L-CYS) stimulated Se-75 uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal jejunum. D-CYS was less effective in the jejunum and similarly effective in the cecum. L-Leucine (L-Leu) and L-glutamic acid significantly reduced the stimulatory effect of L-CYS on Se uptake in the distal jejunum, whereas the respective effect of D-Cys was not diminished by L-Leu. Cysteamine stimulated mucosal Se-75 uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate also enhanced Se-75 uptake in the distal jejunum. The stimulatory effects of L-CYS, mercaptopyruvate, and thioglycolate were Na+-dependent, whereas the effect of cysteamine also occurred in the absence of Na+. Mercaptosuccinate, D-penicillamine, ergothioneine, and thiosulfate did not enhance mucosal Se-75 uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that are rapidly absorbed by the intestinal epithelium through various Na+-dependent and Na+-independent mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence of thiols in the gastrointestinal tract.
