Abstract
Conclusions
Rats respond to short fasts (2 days) without change in arginase concentration in the liver tissue, and adaptations to changes in metabolism are reflected in decreases in the size of the liver. If fasted until near the moribund condition there is increased arginase concentration in the livers of both sexes, with loss of sex differentiation. Adjustment of the quantities of this enzyme by male rats when fasted 8 days is reflected by change in the size of the liver and by increase in its concentration of the enzyme. Adjustments to long fasts by female rats is accompanied by increase in enzyme concentration and after 4 days of fast the quantities of liver tissue are not further decreased. As shown in Fig. 1 fasts of intermediate duration give variable results in the concentration of the enzyme in the livers of male rats. Such variations may be correlated with the type of body materials, carbohydrates and fats (non-nitrogenous) or proteins (nitrogenous), that serve as primary energy sources at the time of sacrifice. Expressed as quantity of enzyme per unit of body weight, arginase activity changes during the adjustment to the expected utilization of proteins as energy sources.
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