Contribution of net hepatic glycogen synthesis to disposal of an oral glucose load in humans

The contribution of hepatic glycogen synthesis to whole body glucose dispos al after an oral glucose load was examined using C-13 nuclear magnetic reso nance (NMR) spectroscopy to measure liver glycogen content in healthy, volu nteers after an overnight fast. In group 1 (n = 14). hepatic glycogen synth esis was measured using C-13-NMR spectroscopy for 240 minutes after ingesti on of 98 +/- 1 g glucose. Liver volumes were measured using magnetic resona nce imaging (MRI). To assess the direct (glucose -->glucose-6-P -->glucose- 1-P --> uridine diphosphate (UDP)-glucose --> glycogen) and indirect (3-car bon units --> --> glycogen) pathways of liver glycogen synthesis, group 2 ( n = 6) was studied with an identical glucose load enriched with [1-C-13]glu cose along with acetaminophen to noninvasively assess the C-13 enrichment i n hepatic UDP-glucose. The fasting hepatic glycogen content was 305 +/- 17 mmol/L liver, end the liver volume was 1.46 +/- 0.07 L. For the initial 180 minutes after ingestion of glucose, hepatic glycogen concentrations increa sed linearly (r = .94, P = .0006) achieving a maximum concentration of 390 +/- 7 mmol/L liver and then remained constant until the end of the study. T he mean maximum rate of net hepatic glycogen synthesis was 0.48 +/- 0.07 mm ol/L liver-minute. Total liver glycogen synthesis could account for 16.7 +/ - 3.8 g (17% +/- 4%) of the glucose ingested, and of this, 10.5 +/- 2.4 g ( 63% +/- 7%) was synthesized by the direct pathway. In conclusion, after ing estion of 98 g of glucose: (1) 16.7 +/- 3.8 g (17% +/- 4%) glucose was stor ed in the liver as glycogen, and (2) 63% +/- 7% (10.5 +/- 2.4 g) of this gl ycogen was formed via the direct pathway. Copyright (C) 2001 by W.B. Saunde rs Company.