The circadian change of gluconeogenesis in the liver in vivo in fed rats.

The circadian change of gluconeogenesis in the liver in vivo in fed rats was studied. Gluconeogenesis in the liver in vivo was determined by measuring the rate of synthesis of 14C-labeled blood glucose derived from a 14C-labeled substrate, such as lactate, pyruvate or an amino acid injected into nephrectomized rats. Gluconeogenesis in the liver from all substrates examined except glutamine was higher at 8:00 P.M. than at 8:00 A.M. in correspondence with the circadian rhythm of the activity of hepatic phosphoenolpyruvate carboxykinase. These data indicate that hepatic gluconeogenesis shows a circadian change in response to changes in nutritional conditions in vivo.