Enhancement of glutathione S-transferase activity in rat liver by repeated administration of propylthiouracil.

Treatment of rats with propylthiouracil for one to two weeks caused an increase in glutathione S-transferase (GST) activity of the liver cytosol, but not of the particulate fraction. Increased GST activity was reversed two weeks after discontinuing PTU administration. Activation of the enzyme was inversely proportional to the decrease in leukocytes. Repeated administration of PTU increased the Vmax of the enzyme without affecting the Km value for the substrate 1-chloro-2,4-dinitrobenzene, whereas both the Km and Vmax for glutathione (GSH) were increased by PTU treatment. GSH content and GSH peroxidase activity were not affected by PTU, but this resulted in an increase in glucose 6-phosphate dehydrogenase activity. PTU treatment caused increase in GST activity using 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, p-nitrobenzyl chloride, and benzalacetone as substrates; enzyme activity towards chlorodinitrobenzene was the highest.