Pathways of hepatic glycogen formation in humans following ingestion of a glucose load in the fed state

The relative contributions of the direct and the indirect pathways to hepatic glycogen formation following a glucose load given to humans four hours after a substantial breakfast have been examined. Glucose loads labeled with [6- 14C]glucose were given to six healthy volunteers along with diflunisal (1 g) or acetaminophen (1.5 g), drugs excreted in urine as glucuronides. Distribution of 14C in the glucose unit of the glucuronide was taken as a measure of the extent to which glucose was deposited directly in liver glycogen (ie, glucose → glucose-6-phosphate → glycogen) rather than indirectly (ie, glucose → C 3-compound → glucose-6-phosphate → glycogen). The maximum contribution to glycogen formation by the direct pathway was estimated to be 77% ± 4%, which is somewhat higher than previous estimates in humans fasted overnight (65% ± 1%, P < 0.05). Thus, the indirect pathway of liver glycogen formation following a glucose load is operative in both the overnight fasted and the fed state, although its contribution may be somewhat less in the fed state.