Effect of protein deficiency on the lysosomal enzyme activities of the spleen and thymus of weanling rats.

The effect of a low protein (4%) diet on the activity of the hydrolytic enzymes ribonuclease, deoxyribonuclease, acid and alkaline phosphatases, beta-glucuronidase and lysozyme has been studied in the spleen and thymus of weanling Wistar rats. Experimentation was carried out over 20 and 30 days, and comparisons were made with well-nourished (12% protein) controls. Body weight decreased during the terminal period in protein-deficient animals (P less than 0.001). Spleen and thymus absolute net weights also dropped significantly (P less than 0.001). In terms of organ weight relative to body weight, there was a clear decrease in thymus compared with controls (P less than 0.001). Enzyme activities expressed per total organ fell significantly. Thus, in spleen at 20 days the decrease was maximum in ribonuclease activity (91.15%) and minimum in acid phosphatase activity (44.09%). Thymus decreases ranged from 83.60% activity in beta-glucuronidase and 93.56% in ribonuclease. At 30 days decreases were accentuated; the maximum value in spleen was 92.34% lysozyme and, in thymus, 97.09% acid phosphatase. A large increase in hydrolytic activity expressed per milligram of protein was registered, especially at 30 days. This increase reached a maximum of 78.08% beta-glucuronidase in thymus and a minimum of 56.1% alkaline phosphatase; acid phosphatase and ribonuclease activities were not modified. In spleen, however, acid phosphatase (34.00%), alkaline phosphatase (62.50%), deoxyribonuclease (39.25%), and beta-glucuronidase (36.01%) increased, but lysozyme and ribonuclease enzymes decreased. We concluded that a low protein diet increases catabolism in spleen and thymus through an enhancement of lysosomal hydrolase activities.