Degree of protein deficiency affects the extent of the depression of the antioxidative enzyme activities and the enhancement of tissue lipid peroxidation in rats.

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.(ABSTRACT TRUNCATED AT 250 WORDS)