Glycogen deposition in adipose tissue: Variations in levels of glycogen-cycle enzymes during fasting and refeeding

The influence of fasting and fasting-refeeding upon the activities of the glycogen-cycle enzymes in rat epididymal adipose tissue has been investigated. In fed (control) animals UDPG-glycogen transglucosylase is the limiting enzyme in the pathway between glucose and glycogen in adipose tissue. Fasting for 48 hours significantly lowered the levels of all of the enzymes of the glycogen cycle, and refeeding of a low-fat, high-carbohydrate diet for either 24 or 48 hours following a 48-hour fast resulted in an apparent sequential return of the enzyme activities in the order in which they appear in the glucose to glycogen pathway. Endogenous glucose-6-phosphate levels in adipose tissue during the various nutritional states were not significantly different from the fed state, and thus the activation of UDPG-glycogen transglucosylase by glucose-6-phosphate apparently does not account for the marked deposition of glycogen which occurs during refeeding.