Effect of Dietary Protein Level on Growth and Liver Enzyme Activities of Rats

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Abstract
The activities of 10 liver enzymes were studied in rats fed diets containing various levels of casein for 15 or 29 days. The enzymes studied were xanthine oxidase, uricase, arginase, glutamic-pyruvic transaminase, glutamic-oxaloacetic transaminase, cathepsin, D-amino acid oxidase, glutamic dehydrogenase, succinic dehydrogenase and alkaline phosphatase. It was found that these liver enzymes could be divided roughly into 4 types with respect to the response curves of these activities obtained by plotting against the dietary protein level. The enzymes of the first type decreased in rats fed protein-free or low protein diets, but did not change greatly after reaching the maximal value with increasing dietary protein levels. These enzymes were xanthine oxidase, succinic dehydrogenase, glutamic dehydrogenase and D-amino acid oxidase. The enzymes of the second type increased with each increase in the dietary protein level; these were arginase, glutamic-pyruvic transaminase, glutamic-oxaloacetic transaminase and uricase. The enzyme of the third type, cathepsin, was essentially unchanged in rats fed diets containing different dietary protein levels. The enzyme of the fourth type, alkaline phosphatase, increased in rats fed protein-free or low protein diets, (29 days feeding). It was shown that the response curves of enzymes included in the first type as liver xanthine oxidase, succinic dehydrogenase and glutamic dehydrogenase were similar to those of liver nitrogen and of the growth rates in animals.

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