Stimulation of mucosal uptake of selenium from selenite by some thiols at various sites of rat intestine

Abstract

The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of75Se from75Se-labeled selenite (conc. 10 μmol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term uptake technique. l-Cysteine (l-Cys) stimulated75Se 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 mucosal75Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate also enhanced75Se uptake in the distal jejunum. The stimulatory effects of l-Cys, mercaptopyruvate, and thiologlycolate were Na+-dependent, whereas the effect of cysteamine also occurred in the absence of Na+. Mercaptosuccinate, d-penicillamine, ergothioneine, and thiosulfate did not enhance mucosa75Se 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. © 1992 Humana Press Inc.