Utilization of glutathione disulfide as cysteine source during long-term parenteral nutrition in the growing rat

Utilization of intravenously administered glutathione disulfide was investigated during long-term parenteral nutrition in growing rats. In a series of cross-over studies, three solutions were tested against one another by recording weight gain, nitrogen balance, and plasma amino acid patterns. Solution 1 contained the required amount of methionine for rats, solution 2 had only one third of the required methionine, but was made isonitrogenous with glycine, whereas in solution 3, two thirds of the methionine was replaced by glutathione disulfide. Weight gain was about twice as high during infusion with either the required amount of methionine or the glutathione disulfide when compared with solution 2. Nitrogen retention was significantly higher during infusion with sufficient methionine or a corresponding amount of glutathione disulfide, when compared with the solution low in methionine. Plasma levels of cystine decreased significantly under the low methionine supply, but no difference was observed for the groups receiving sufficient methionine or the corresponding amount of glutathione disulfide. It is concluded that glutathione disulfide permits adequate cysteine supply in parenteral nutrition and may replace part of the methionine in the presence of an impaired conversion of methionine to cysteine.