Carbohydrate supply as a regulator of rat liver phosphoenolpyruvate carboxykinase activity.

Administration of glucose, fructose, and glycerol to fasted rats produced a significant depression of liver phosphoenolpyruvate carboxykinase activity within 4 to 8 hours; galactose and ribose were much less effective. All the compounds yielded appreciable quantities of liver glycogen. The depression of phosphoenolpyruvate carboxykinase activity by glucose and glycerol was diminished by the concomitant administration of 2-deoxyglucose. The latter depressed glycogen formation from administered carbohydrate in muscle but not in liver. In rats made diabetic by alloxan, depression of elevated phosphoenolpyruvate carboxykinase activity by insulin was dependent upon a dietary source of carbohydrate. These results were interpreted to indicate that depression of certain gluconeogenic enzymes after carbohydrate ingestion is initiated by the metabolism of carbohydrate in some extrahepatic site.