Enzymes of mercapturic acid production in rat mammary gland.

1. The enzymes glutathione S-transferase, gamma-glutamyl peptidyltransferase and dipeptidase, which participate in the detoxification pathway through mercapturic acid production, were measured in rat mammary gland during pregnancy and lactation. 2. Mammary-gland concentration of reduced glutathione showed, concomitantly with the enzyme activities, a significant increase during lactation. 3. The mammary-gland glutathione S-transferase exhibits characteristics quite similar to those described for the liver and kidney enzymes with respect to substrates, isoenzymes, molecular weight and probenecid and bilirubin inhibition. 4. In view of these similarities, mammary-gland glutathione S-transferase may play the same role as a cytoplasmic organic-anion receptor proposed for the hepatic enzyme. It may also represent a detoxification pathway for protecting the mammary tissue during the lactogenic cycle.