The protease inhibitor leupeptin decreases protein degradation in rat skeletal and cardiac muscle incubated in vitro, while protein synthesis remains unaltered. Leupeptin also lowers protein breakdown in denervated rat muscles and affected muscles from mice with hereditary muscular dystrophy. Leupeptin may thus be useful in retarding tissue atrophy. Since homogenates of leupeptin-treated muscles had decreased cathepsin B activity, this lysosomal protease may play a role in protein turnover in normal and diseased muscles.
