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Dietary Effects on Rat Liver Enzymes in Meal-fed Rats¹

Department of Physiological Sciences, School of Veterinary Medicine, University of California, Davis, California

The effects of dietary changes and starvation were studied in meal-fed, male rats of the Sprague-Dawley strain following a training period of 2 weeks and a period of protein deprivation of 4 days. A 90% casein diet increased the activities of the enzymes glucose 6-phosphatase, glucose 6-phosphate dehydrogenase, serine dehydrase, tyrosine--ketoglutarate transaminase, glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase 24 hours after the meal. Serine dehydrase and glutamic-oxaloacetic transaminase activities were further increased in animals killed 48 hours after the protein meal. An increase in the activity of serine dehydrase was also observed in rats killed 48 hours after their last protein-free meal. The feeding of diets which contained both carbohydrate (either glucose or fructose) and casein, increased glucose 6-phosphate dehydrogenase and malic enzyme activities to a greater extent than the 90% casein diet, but the increases in transaminase activities were less than those obtained by feeding the 90% casein diet. Serine dehydrase activity was not increased by a 65% carbohydrate diet and was increased only slightly by diets containing 57.5% casein plus 32.5% carbohydrate. Tyrosine--ketoglutarate transaminase activity was increased by this latter diet almost as well as by the 90% casein diet. The inducing effect of carbohydrates on enzyme activities was observable, even if the test diets contained considerable amounts of protein, whereas the inducing effect of protein was considerably decreased by even a moderate amount of carbohydrate.

Manuscript received 22 March 1968.