Regulatory role of glucose-6 phosphatase in the repletion of liver glycogen during refeeding in fasted rats

We analyzed the biochemical mechanisms involved in the liver glycogen reple tion upon refeeding for 360 min in 48 and 96 h-fasted rats. In 48 h-fasted rats, the glycogen synthesis involved a rapid and further sustained inducti on of glucokinase (GK) (increased twice from 90 min) and a rapid but transi ent activation of glycogen synthase a (GSa) (maximal increase by 150% at 90 min). It did not involve the inhibition of glycogen phosphorylase a (GPa). In 96 h-fasted rats, the glycogen repletion did not involve the induction of GK for the first 180 min of refeeding. It involved a slow activation of GSa (maximal 150% increase at 180 min) and a rapid inhibition of cpa (signi ficant from 90 min, maximal 50% inhibition by 180 min). In both groups of r ats, there was a progressive inhibition of the glucose-6 phosphatase (Glc6P ase) activity (maximal suppression by 30% in both groups at 360 min). These results highlighted a key role for the inhibition of Glc6Pase activity in the liver glycogen repletion upon refeeding. (C) 1999 Elsevier Science B.V. All rights reserved.