Degree of Protein Deficiency Affects the Extent of the Depression of the Antioxidative Enzyme Activities and the Enhancement of Tissue Lipid Peroxidation in Rats

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Abstract
To investigate the effects of various dietary protein levels on tissue lipid peroxidation and antioxidative enzyme activities, four groups of Long-Evans male weanling rats were fed a 6, 8, 12 or 20% lactalbumin diet for 6 wk. The red blood cell in vitro spontaneous hemolysis values were 28.6, 24.9, 18.9 and 14.1% for the rats fed the 6, 8, 12 and 20% lactalbumin diets, respectively. The thiobarbituric acid-reactive substances (TBARS) in plasma, RBC, liver, kidney, muscle, lung, spleen and heart were lowest in the group fed the 20% lactalbumin diet. Rats fed the diet containing 12% lactalbumin had significantly greater TBARS in plasma, spleen, kidney and muscle compared with rats fed the 20% lactalbumin diet. Rats fed the 8% lactalbumin diet had markedly higher TBARS levels (P < 0.05) in all tissues examined than did those fed the 12% lactalbumin diet. The TBARS in all eight tissues of the rats fed the 6% lactalbumin diet were even higher than those of rats fed the 8% lactalbumin diet (P < 0.05). The activities of glutathione peroxidase, superoxide dismutase and glucose-6-phosphate dehydrogenase in RBC were gradually lowered (P < 0.05) when the dietary protein level was decreased stepwise. The activities of these antioxidative enzymes in liver also were reduced significantly when dietary protein level decreased from 20 to 12% and then to 8%. These enzyme activities in the rats fed the diet containing 6% lactalbumin generally were not different from those of the rats fed 8% lactalbumin. Thus, the degree of protein deficiency affects the extent of the depression of the antioxidative enzyme activities and the enhancement of tissue lipid peroxidation.