Time course and significance of changes in hepatic fructose-2,6-bisphosphate levels during refeeding of fasted rats.
The time course of changes in hepatic fructose-2,6-bisphosphate (F-2,6-P2) and glycogen content was examined in fasted rats infused with glucose intragastrically or allowed to eat a chow diet ad lib. Initial values for the two parameters were approximately 0.4 nmol/g and 2 mg/g of tissue, respectively. Contrary to what might have been expected on the basis of reported studies with hepatocytes exposed to glucose (i.e., a rapid elevation of F-2,6-P2), the rise in F-2,6-P2 levels in vivo was a late event. It began only 4-5 h after glucose administration or refeeding, at which time glycogen content had reached approximately 35 mg/g of tissue. Thereafter, [F-2,6-P2] climbed rapidly, attaining fed values in the region of 10 nmol/g as glycogen stores became maximal (approximately 60 mg/g of tissue). Although the biochemical basis for these changes is still unclear, the delayed increase in [F-2,6-P2] is entirely consistent with the fact that much of the glycogen deposited in liver in the early postprandial phase is gluconeogenic in origin. The later rise in [F-2,6-P2] likely represents a key signal for the attenuation of gluconeogenic carbon flow into glycogen as the latter approaches repletion levels.
D000818:Animals; D004435:Eating; D005215:Fasting; D005635:Fructosediphosphates / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006598:Hexosediphosphates / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D005635:Fructosediphosphates; D006598:Hexosediphosphates; D008112:Liver Glycogen; C027652:fructose 2,6-diphosphate; D005947:Glucose