CONTRIBUTION OF NET HEPATIC GLYCOGENOLYSIS TO GLUCOSE-PRODUCTION DURING THE EARLY POSTPRANDIAL PERIOD

Relative contributions of net hepatic glycogenolysis and gluconeogenes is to glucose production during the first 12 h of a fast were studied in 13 healthy volunteers by noninvasively measuring hepatic glycogen c ontent using C-13 nuclear magnetic resonance spectroscopy. Rates of ne t hepatic glycogenolysis were calculated by multiplying the change in liver glycogen content with liver volume determined by magnetic resona nce imaging. Rates of gluconeogenesis were calculated as the differenc e between rates of glucose production determined with an infusion of [ 6,6-H-2]-glucose and net hepatic glycogenolysis. At 6 P.M. a liquid mi xed meal (1,000 kcal; 60% as glucose) was given, to which [2-H-2]gluco se was added to trace glucose absorption. Hepatic glycogen content was measured between 11 P.M. and 1 A.M. and between 3 and 6 A.M. At 11 P. M. the concentration was 470 mM and it decreased linearly during the n ight. The mean liver volume was 1.47 +/- 0.06 liters. Net hepatic glyc ogenolysis (5.8 +/- 0.8 mu mol . kg body wt(-1) . min(-1)) accounted f or, on average, 45 +/- 6% and gluconeogenesis for 55 +/- 6% of the rat e of whole body glucose production (12.6 +/- 0.6 mu mol . kg body wt(- 1) . min(-1)). In conclusion, this study shows that, even early in the phase of the postabsorptive period when liver glycogen stores are max imal, gluconeogenesis contributes similar to 50% to hepatic glucose pr oduction.