Transport of L-cysteine and reduced glutathione through biological membranes.

Comparative studies were carried out on in vivo and in situ absorption in rats and in vitro uptake by red cells of L-cysteine (CySH) and reduced glutathione (GSH). After oral administration of CySH, the plasma and liver CySH levels and liver GSH level significantly increased, but the plasma GSH level did not. In contrast to the results with CySH, when GSH given orally at a dose equivalent to that of CySH either on a weight or molar base, no increase in the levels of GSH was observed at either dose level. In a rat small intestine recirculation system in situ, CySH added to the recirculation perfusate disappeared progressively with time from the perfusate, indicating that transportation occurred across the intestinal wall, but with GSH such disappearance was not observed. CySH was taken up well by rabbit erythrocytes in vitro, but GSH was not. It was concluded, therefore, that CySH passes through biological membranes and serves as a good source of SH groups, whereas GSH is ineffective when given orally because of its poor absorption from the digestive tract and/or poor ability to permeate through the membrane.