The absorption of cystine and cysteine from rat small intestine

Abstract

The absorption of isomers of cystine and cysteine from the small intestine of the rat has been studied with a lumen-perfusion (in situ) and an everted-sac technique. Tissue potassium and water contents, histological examination and application of functional tests have been used to assess the condition of the intestinal tissue in the preparations. The rates of absorption of both L-cystine and L-cysteine were found to increase approximately linearly with increasing concentration. The rates of absorption from duodenum, jejunum, and ileum were found to decrease in that order. The absorption of L-cystine but not D-cystine has been shown to be an active process. Evidence is presented which shows that a similar process is probably also involved in the absorption of L-cysteine. Previous work which demonstrated no difference between the rates of absorption of the D- and L-isomers of cystine is discussed in the light of the experiments reported here.