Some enzymic changes in the mammary gland of rats during pregnancy, lactation and mammary involution

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Abstract
Changes in the activity of glutamic dehydrogenase, glutamic-aspartic transaminase, cathepsin and beta-glucuronidase were studied in the mammary gland of the rat at various stages during pregnancy, lactation and mammary involution. The activities of glutamic dehydrogenase and glutamic-aspartic transaminase increase only slightly during pregnancy, but rise sharply after parturition to a high level which is maintained throughout lactation, falling precipitously after weaning. Beta-glucuronidase activity increases sharply between the 15th and 20th days of pregnancy but then falls progressively over the period of lactation. There is a large increase in beta-glucuronidase after weaning during the period of mammary involution. The catheptic activity of the gland increases progressively from the 10th day of pregnancy up to the 20th day of lactation and it increases even further during mammary involution. The results are discussed in relation to possible changes in the mitochondria during the lactation cycle and the possible function of these enzymes in providing precursors for the synthesis of milk protein.