Metabolic response to a glucagon challenge varies with adiposity and life-history stage in fasting northern elephant seals.
Metabolic adaptations for extended fasting in wildlife prioritize beta-oxidation of lipids and reduced glucose utilization to support energy metabolism. The pancreatic hormone glucagon plays key roles in regulating glycemia and lipid metabolism during fasting in model species but its function in wildlife species adapted for extended fasting is not well understood. Northern elephant seals (NES) undergo natural fasts of 1-3months while under constraints of high nutrient demands including lactation and development. We performed a glucagon challenge on lactating, molting and developing NES, early and late in their natural fasts, to examine the impact of this important regulatory hormone on metabolism. Glucagon caused increases in plasma glucose, insulin, fatty acids, ketones and urea, but the magnitude of these effects varied widely with adiposity and life-history stage. The strong impact of adiposity on glucose and insulin responses suggest a potential role for adipose derived factors in regulating hepatic metabolism and pancreatic sensitivity. Elevations in plasma glucose in response to glucagon were strongly associated with increases in protein catabolism, suggesting negative impacts of elevated glucagon on protein sparing. Glucagon promoted rapid ketone accumulation suggesting that low ketoacid levels in NES reflect low rates of production. These results demonstrate strong metabolic impacts of glucagon and support the idea that glucagon levels are downregulated in the context of metabolic adaptation to extended fasting. These results suggest that the regulation of carbohydrate and lipid metabolism in NES changes with adiposity, fasting duration and under various constraints of nutrient demands.
Sonoma State University, Rohnert Park, CA 94928, USA. Electronic address: crocker@sonoma.edu.
Daniel E
DE
Crocker
Sonoma State University, Rohnert Park, CA 94928, USA; Simon Fraser University, Burnaby, BC V5A 1S6, Canada.
Melinda A
MA
Fowler
Sonoma State University, Rohnert Park, CA 94928, USA; National Marine Mammal Foundation, San Diego, CA 92106, USA.
Cory D
CD
Champagne
Sonoma State University, Rohnert Park, CA 94928, USA.
Anna L
AL
Vanderlugt
Sonoma State University, Rohnert Park, CA 94928, USA; National Marine Mammal Foundation, San Diego, CA 92106, USA.
Dorian S
DS
Houser
D050154:Adiposity / Q000187:drug effects*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects; D005215:Fasting / Q000502:physiology; D005260:Female; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D007774:Lactation / Q000187:drug effects / Q000378:metabolism; D008018:Life Cycle Stages / Q000187:drug effects*; D050356:Lipid Metabolism / Q000187:drug effects; D046048:Seals, Earless / Q000254:growth & development / Q000378:metabolism*
D001786:Blood Glucose; D005765:Gastrointestinal Agents; D007328:Insulin; D005934:Glucagon
Fasting metabolism; Glucagon; Gluconeogenesis; Lipolysis; Pinniped