30.6 Thursday, Jan. 5 Lactate turnover and glucose production in free-ranging northern elephant seal pups Mirounga angustirostris. TAVONI, Stephen*; CHAMPAGNE, Cory; HOUSER, Dorian; CROCKER, Dan; Sonoma St. Univ.; UC Santa Cruz; National Marine Mammal Foundation; Sonoma St. Univ. email@example.com
The most extreme examples of fasting adaptation are species that undergo natural fasts during energy intensive periods. These species must conserve tissues while fasting under the constraint of high rates of nutrient commitment to energy metabolism or development. Elephant seal pups Mirounga angustirostris combine a post weaning fast with development of diving capacity. During this period they undergo dramatic changes in blood volume and blood and muscle respiratory pigments that are critical to foraging effectively in the marine environment. Elephant seals lack the characteristic suppression of glucose metabolism during fasting; production greatly exceeds the estimated needs of glucose dependent tissues and gluconeogenesis from glycerol and amino acid precursors is minor. This suggests high rates of glucose carbon recycling, potentially through Cori cycle activity. To investigate this hypothesis, lactate and glucose turnover rates were measured by a primed constant infusion of [U-14C] lactate and 3H- labeled glucose. Measurements were taken after 14 and 35 days of fasting in 8 weaned pups. When controlled for changes in body mass, glucose and lactate turnover rates did not change across the fast. Lactate turnover varied significantly with glucose turnover, suggesting glycolytic flux as a major avenue of glucose disposal. The minimum lactate contribution to glucose production was high (>33%) and increased across the fast, supporting the hypothesis that high rates of glucose turnover in fasting elephant seals are due to glucose recycling. These features may be adaptive in the prevention of ketoacidosis while fasting and are consistent with metabolic defenses associated with hypoxia.