Lysosomal enzyme changes in enforced mammary-gland involution.

1. Changes occurring in the activities and latency of acid ribonuclease and beta-glucuronidase have been studied in rat mammary gland during the early phases of mammary involution. 2. It was found that there were rapid increases in the proportions of both enzymes in the ;free' (i.e. unsedimentable) form. The total activities of both enzymes did not show the rapid decrease characteristic of most other enzymes studied during mammary-gland involution. 3. The effects of pretreating the rats with reserpine or the antihistamine drug Phenergan on these lysosomal changes was studied. Neither treatment affected the enzymic redistribution that occurs during early involution. 4. It was concluded that lysosomal rupture occurs as an early manifestation of mammary-gland involution. Although reserpine treatment preserves the histological appearance of the gland and, apparently, inhibits involution, this drug did not prevent the lysosomal changes normally found in suspensions.