Tissue glutathione as a cyst(e)ine reservoir during fasting and refeeding of rats

Previous reports suggest that liver glutathione serves as a cyst(e)ine reservoir in both starved rats and rats fed a cyst(e)ine-deficient diet. We investigated whether glutathione concentrations in other tissues also decrease and whether component amino acids of glutathione increase under such conditions. Tissue glutathione and free amino acid concentrations were measured in six groups of growing rats (120-150 g; four animals/group) during fasting and refeeding regimens. All animals were fed a rat stock diet ad libitum for 5 days. Two groups were than fasted for 24 or 48 hours, respectively. Other groups were fasted for 48 hours and then refed for 10, 24 or 48 hours respectively the stock diet. Significant changes (P less than or equal to 0.05) in liver and intestine glutathione concentrations were noted with 24 and 48-hour fasting, and a 24-hour refeeding was necessary to return concentrations to prefasting values. Muscle glutathione concentrations decreased slightly with fasting, but remained low with refeeding. Erythrocyte glutathione concentrations were independent of dietary treatment. Liver cysteine and glycine concentrations increased after 24 hours' fasting, but glutamate levels were not affected. The data indicate that liver and intestine glutathione serve as cyst(e)ine reservoirs during fasting. Since erythrocyte and muscle glutathione levels did not decrease, levels in these tissues cannot be used to measure cyst(e)ine status in premature infants fed parenterally.