Alterations in the Activities of Several Rat Liver Enzymes at Various Times after the Feeding of High Carbohydrate Diets to Rats Previously Adapted to a High Protein Regimen

Abstract

The effect of high carbohydrate (protein-free) diets on the activities of several rat liver enzymes was studied in rats previously adapted to a 90% casein, carbohydrate-free diet. Both, the 90% glucose and the 90% fructose diet, were found to decrease all the liver constituents and enzyme activities studied, with the exception of pyruvate kinase, the activity of which was increased temporarily by both carbohydrate diets. The possibility of a control system regulating the synthesis of this enzyme at the translation level is discussed. Phosphorylase, glucose 6-phosphatase, fructose 1,6-diphosphatase, L-α-glycerophosphate dehydrogenase, glucose 6-phosphate dehydrogenase and malic enzyme activities were decreased to variable amounts. In some cases glucose 6-phosphate dehydrogenase and malic enzyme activities were increased. Tyrosine-α-ketoglutarate transaminase activity was minimal after 1 day of carbohydrate feeding. Glutamic-oxaloacetic transaminase, glutamic-pyruvic transaminase and serine dehydrase activities declined logarithmically. In the glucose-fed animals glutamic-oxaloacetic transaminase declined with a half-life of 4 days, glutamic-pyruvic transaminase with a half-life of 2 days and serine dehydrase with a half-life of 1.7 days. Fructose feeding increased the half-life of both glutamic-oxaloacetic transaminase and glutamic-pyruvate transaminase but not the half-life of serine dehydrase. Pair-feeding experiments showed that the tendency of the fructose diet to increase liver size and the half-lives of the 2 transaminases (glutamic-oxaloacetic transaminase and glutamic-pyruvate transaminase) was not due to an increased consumption of the fructose diet.