[Microdensitometric measurement enzyme activities in the mammary gland of the mouse]

The myoepithelium of developing, lactating, and involuting mammary gland of the mouse exhibits a high alkaline phosphatase activity. The content of the alveoli and the apical plasma membrane of gland cells histochemically show enzyme activity before and after lactation but not during milk secretion. In the course of involution the alveoli shrink in size and the reaction of alkaline phosphatase becomes stronger in the gland tissue. In whole breast tissue the enzyme activity decreases, because in this time a great part of the alveoli are degraded and replaced by connective tissue and fat. As measured by a scanning microdensitometer the activity of some oxydoreductases (3-hydroxybutyrate dehydrogenase, lactate dehydrogenase, malate dehydrogenase, and succinate dehydrogenase) increase in proceeding development of the mammary gland and reach their highest level at the time of lactation. Already 12 h after the start of involution the oxydoreductases loose 30 to 50% of their activity and undergo a further reduction 3 to 4 days later. On the other side the activity of lysosomal enzymes increase during involution. beta-Glucuronidase and leucine aminopeptidase have their highest activity in the early stage of involution, whereas acid phosphatase predominate in the late period of gland degradation.