Effect of methionine sulfoximine on glutathione and amino acid levels in the nephron.

The effect of L-methionine-DL-sulfoximine (MSO) on renal glutathione concentration and aspartic acid transport has been studied by analyses of parts of individual freeze-dried glomeruli, early and late proximal convoluted, early and late proximal straight, and distal straight and convoluted tubules, and patches from thinlimb and papilla areas. Glutathione normally varies threefold along the kidney nephron, being highest in the convoluted and early straight proximal tubule, lowest in the distal straight tubule. Large loads of aspartate cause 20% diminution of glutathione in outer cortex, due entirely to changes in proximal tubule segments. MSO alone lowers glutathione 90% in all parts of the proximal tubule, with no change elsewhere. MSO does not affect the large increase in aspartate in proximal tubules caused by saturating aspartate loads, suggesting that glutathione is not directly involved in transport of this amino acid. Aspartate loads cause a large increase in renal glutamine, which is especially marked in the proximal straight tubule. MSO effectively blocks this increase and depresses tissue glutamine below normal levels.