Effect of Exercise on Liver Protein Loss and Lysosomal Enzyme Levels in Fed and Fasted Rats

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Abstract
Exhaustive treadmill running caused a significant decrease in hepatic protein levels. The rate of protein loss was 0.23 g/h. This protein loss was accompanied by an increase in the activities of free (nonsedimentable) cathepsin D and arylsulfatase, suggesting the involvement of lysosomes. A 24 h fast lowered the liver protein levels by .apprx. 20%. Plots of liver protein levels vs. the time to reach exhaustion showed that the absolute rate of protein loss was the same for fed and the fasted rats. Since the initial protein levels were lower in the fasted rats, their relative rate of protein loss was greater. The level of activity of free (nonsedimentable) cathepsin D and arylsulfatase increased as the time to exhaustion increased in the fed and fasted animals. The increase was severalfold greater in the fasted animals; evidently fasting alters the structure of lysosomes in a way that enhances the increase in lysosomal fragility caused by exercise.