Alterations in the Activities of Several Rat Liver Enzymes at Various Times after Initiation of a High Protein Regimen

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Abstract
The purpose of these experiments was to investigate the time course of increase of several rat liver enzymes following the feeding of a high protein diet (90% casein and carbohydrate-free). Male Sprague-Dawley rats, 6–8 weeks old and weighing 150–200 g were fed a 90% glucose, protein-free diet for 4 days in order to obtain maximal responses in activity after the dietary change. The animals were killed and liver enzyme activity was determined at 0, 1, 2, 3, 4 and 7 days after the rats were offered the high protein diet. All the enzymes studied, with the possible exception of phosphorylase, were increased by the high protein diet. Two patterns of increases in enzyme activity were observed. A number of enzymes including glucose 6-phosphatase, L-α-glycerophosphate dehydrogenase, pyruvate kinase, malic enzyme and tyrosine-α-ketoglutaric transaminase reached a maximum activity within 48 hours or earlier after the change in diet and either remained nearly constant or declined with time. The activities of another group of enzymes including fructose 1,6-diphosphatase, glucose 6-phosphate dehydrogenase, glutamic-oxalacetic transaminase, glutamic-pyruvic transaminase and serine dehydrase rose sharply on the second and third day after the dietary change and the time course of increase appeared to approximate a sigmoidal curve.