Dietary Regulation of Liver Glucose-6-Phosphate Dehydrogenase in the Rat: Starvation and Dietary Carbohydrate Induction

Abstract

The previously reported dietary carbohydrate dependence of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and pyruvate kinase of rat liver has been further explored in rat liver cytoplasm under various conditions of starvation and refeeding. Similar but smaller influences of dietary carbohydrate were found on adrenal and on liver mitochondrial enzyme levels. In liver cytoplasm, glycogen accumulation appeared to be a precursor of the carbohydrate-dependent enzyme increases and, if so, could explain the increase in these enzymes following high dietary protein as well as carbohydrate. Orotate incorporation into liver nuclear RNA was seen after challenge of fasted rats with the high sucrose diet but not after challenge with the high fat diet. Actinomycin D and cycloheximide blocking of enzyme synthesis at zero time and cycloheximide but not actinomycin D blocking of enzyme increase several hours after sucrose indicates transcription level induction of synthesis following high sucrose diet feeding. The data seem consistent with regulation of these enzymes by the tissue levels of their specific substrates. The enzyme increases appear to involve fresh messenger RNA synthesis.