Increase in cathepsin D activity in rat brain in aging

Cathepsin D‐like activity in homogenates of five brain areas of 3‐month‐old and 24‐month‐old Fischer 344 rats was measured. With hemoglobin as substrate at pH 3.2, more than 90% of the activity was inhibited by pepstatin. In each area studied, activity was more than twice as high in the old rat brain: 140–160% higher in the cortex, cerebellum, pons‐medulla, and striatum and 90–100% higher in the hippocampus and spinal cord. The greatly increased metabolic capacity in the absence of an increase in protein turnover may have a role in age‐related pathological degeneration in the brain.