Effects of brief starvation on brain protease activity.

Changes in the activity of proteases (cathepsin D and calpains) caused by 48-h food withdrawal were studied in the brain, liver, kidney, spleen, and heart of 3-, 12-, and 24-month-old Fischer rats. Cathepsin D activity was similar in brain, liver, and heart of control animals; in kidney it was 5-fold higher and in spleen about 10-fold higher. With age, activity increased in all organs tested except spleen. Brief starvation caused no change of cathepsin D activity in brain, but caused an increase in liver and a decrease in spleen. Neutral proteolytic activity in control was highest in the pons-medulla-cerebellum fraction of brain, and activity in liver and heart was below that in brain. Activity increased with age in brain and decreased in other organs. Brief starvation in young animals caused an increase in activity in brain, and a decrease in liver and spleen. Isolated calpain II activity was high in control brain. It increased with age in the cerebrum. Brief starvation resulted in a decrease in the brain. The results indicate that the protease content of the brain is altered with age and in malnutrition, with changes not being the same for all proteases, and changes in brain being different from those in other organs.