Quantification of the pathways followed in hepatic glycogen formation from glucose.

Quantitative contributions of the direct and indirect pathways to liver glycogen formation from a glucose load have been estimated from 1) the distribution of label in glycogen formed from specifically carbon-labeled loads of glucose, 2) the specific activity of the glycogen compared with that of the circulating glucose, 3) the 3H:14C ratios in glycogen formed from loads specifically labeled with 3H and 14C, 4) the incorporation of 3H from 3H2O into the glycogen, and 5) the balance of glucogenic substrates across the splanchnic bed. A number of assumptions are made in the use of each of these methods. Estimates have been made for animals and humans fasted overnight or longer. Results obtained with the different methods are compared. Under these conditions, the contribution of the pathways appears to be determined by the size of the load, with larger contributions of the indirect pathway occurring with smaller loads.