CHAMPAGNE, CD*; HOUSER, DS; CROCKER, DE; Sonoma State University; Sonoma State University; Sonoma State University: Physiological Adaptations to Fasting in northern elephant seals

During prolonged fasting physiological mechanisms defend lean tissue from catabolism. In the fasting state, glucose is derived solely from gluconeogenesis, requiring some catabolism of amino acids for gluconeogenic substrates. This creates a conflict in animals undergoing fasts concurrently with metabolically challenging activities. We investigated glucose metabolism while fasting in northern elephant seals during neonatal development and during lactation. Glucose production and glucose cycle activity were measured in weaned elephant seal pups early (2 weeks) and late (6 weeks) in the postweaning fast, and in lactating adults early (5 days post-partum) and late (21 days post-partum) in the lactation period. Glucose cycle activity was highly variable throughout the study period and did not change over fasting duration. Endogenous glucose production (EGP) in weanlings was 2.8 (�0.7) mg·(kg·min)^-1 early and 2.2 (�0.1) during late fasting; in adults EGP was 1.6 (�0.3) mg·(kg·min)^-1 during early lactation and 1.7 (� 0.4) during late lactation. Additionally we investigated the role of regulatory hormones on glucose production and glucose cycle activity. In weanlings, insulin did not change over the study period and values were low compared to other fasting species, while glucagon increased over the fast (t = 2.96, p = 0.03). In lactating adults, insulin decreased over fasting duration (t = 6.48, p < 0.001), while glucagon remained constant. Insulin to glucagon molar ratio decreased in both weanlings and lactation study groups (t = 5.27, 3.15; p = 0.003, 0.012). The glucose production values measured in this study were surprisingly high in all study groups and exceed the estimated gluconeogenic substrate available. These data suggest extensive glucose recycling via Cori cycle activity occurring in northern elephant seals.