Modulation of gamma-glutamyl cycle and glutathione levels in rat mammary gland explants.

: The reduced glutathione levels and the enzymes gamma-glutamyl-transpeptidase, 5-oxoprolinase and gamma-glutamylcysteine synthetase, which participate in the metabolism of glutathione through the gamma-glutamyl cycle, were determined in explants from the lactating mammary gland of the rat. Significant activities of the enzyme were found. Two modulators of this cycle were used. L-2-Oxothiazolidine-4-carboxylate, an alternative substrate of 5-oxoprolinase and an intracellular cysteine delivery system, increased the reduced glutathione levels under the experimental conditions used. The other compound utilized, DL-buthionine-SR-sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase, significantly decreased the glutathione levels. This effect is slowly reversible.