44.3 Tuesday, Jan. 5 A complete profile of carbohydrate metabolism during prolonged fasting in the northern elephant seal CHAMPAGNE, CD*; FOWLER, MA; COSTA, DP; HOUSER, DS; CROCKER, DE; UC Santa Cruz; UC Santa Cruz; UC Santa Cruz; Sonoma State University; Sonoma State University email@example.com
During prolonged fasting, glucose derives from gluconeogenesis and is required as an energy source by some tissues (e.g. CNS, erythrocytes). Glucose production is typically suppressed while fasting to reduce strains on protein reserves resulting from the commitment of amino acids to gluconeogenesis. Previous work in fasting northern elephant seals, however, has found elevated rates of glucose production. To further investigate carbohydrate metabolism during prolonged fasting in elephant seals, this study used a recently developed tracer technique utilizing D2O, [U-13C]propionate, and a continuous infusion of [1,6-13C]glucose. We used nuclear magnetic resonance (NMR) to measure the abundance of each resulting positional isotopomer of glucose. Relative peak heights from the resulting NMR spectra were used to quantify the rate of glucose production, the contribution of major gluconeogenic precursors (glycerol, glycogen, and phosphoenolpyruvate (PEP)) to glucose production, the flux through the tricarboxylic-acid cycle, and the activity of the PEP cycle. The contribution of glycerol to gluconeogenesis was low, only 5% of glucose production, confirming recent measurements of glycerol gluconeogenesis. Less than one-fifth of glucose flux was derived from glycogen with the balance derived from PEP. The significant contribution of PEP to glucose production is consistent with our previous suggestion that the elevated rates of glucose production observed in elephant seals are due to recycling through three-carbon intermediates such as lactate. This is the first use of this positional isotopomer technique in a free-ranging animal and provides the first comprehensive carbohydrate metabolism profile of an animal undertaking a prolonged fast.