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Effect of Protein Deficiency on the Lysosomal Enzyme Activities of the Spleen and Thymus of Weanling Rats

Departmento de Fisiología Animal, Facultad de Farmacia, Universidad Complutense, Madrid-3-Spain

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 < 0.001). Spleen and thymus absolute net weights also dropped significantly (P < 0.001). In terms of organ weight relative to body weight, there was a clear decrease in thymus compared with controls (P < 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 56.41% 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.

KEY WORDS: • lysosomal enzymes • protein deficiency

Manuscript received 12 March 1981.