The influence of nitrate on unidirectional Na' and C1-fluxes across the sheep rumen epithelium was investigated. Nitrate, an inhibitor of CI-/HCO< exchange, significantly reduced the mucosal-toserosal C1-flux, whereas the serosal-to-mucosal flux was not influenced in the presence of nitrate. This resulted in an almost complete reduction of net C1-absorption. Nitrate had no influence on unidirectional Na+ fluxes. The results indicate that the Cl-/HCO< exchange mechanism is the major route of C1-absorption across the rumen epithelium. Furthermore, nitrate is probably also absorbed by this mechanism.
The influence of cysteine (Cys) on mucosal uptake of 75Se-labeled selenite in sheep midjejunum was investigated using a short-term uptake technique. L-Cys (concn.: 1.0 mmol/L) significantly stimulated uptake of Se from selenite (concn.: 10 mumols/L). The stimulatory effect of L-Cys on mucosal uptake of Se from selenite was Na(+)- and pH-dependent. In the absence of Na+, or at an acidic pH (5.0), the stimulatory effect of L-Cys was abolished. L-alanine and L-lysine, but not L-glutamic acid inhibited uptake of Se from selenite in the presence of L-Cys. Preincubation of mucosal preparations with 10 mmol/L L-Cys produced enhanced mucosal uptake of Se from selenite. It is concluded from these results that L-Cys stimulates absorption of Se from selenite probably by generation of selenodicysteine and maybe cysteine selenopersulfide that are subsequently transported across the intestinal brush border membrane by Na(+)-dependent amino acid carriers. Furthermore, intracellular generation of selenodicysteine might contribute to the uptake of Se from selenite by maintaining the concentration gradient for diffusive uptake of selenite.
In ruminants as well as in simple-stomached animals an efficient entero-hepatic circulation of bile salts is necessary for optimal absorption of dietary fats. However, detailed knowledge about the intestinal absorption of bile salts in ruminants is lacking. We have therefore investigated absorption of taurocholate at various sites of sheep small intestine in vitro by employing a short-term mucosal uptake technique. Furthermore, Na+-dependence of mucosal taurocholate uptake was examined. The results clearly show that in sheep Na+-dependent uptake of taurocholate occurs in the mid-jejunum as well as in the ileum, but not in the proximal jejunum. The activity of mucosal taurocholate uptake increased from proximal to distal with the greatest uptake rates in the ileal segment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.