Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris).
We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3 months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT(3)) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T(4) to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts.
Department of Biology, Sonoma State University, Rohnert Park, CA 94928, USA. crocker@sonoma.edu
Daniel E
DE
Crocker
Rudy M
RM
Ortiz
Dorian S
DS
Houser
Paul M
PM
Webb
Daniel P
DP
Costa
D020155:3-Hydroxybutyric Acid / Q000097:blood; D000222:Adaptation, Physiological; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001806:Blood Urea Nitrogen; D001823:Body Composition; D001947:Breeding; D004734:Energy Metabolism; D005215:Fasting / Q000097:blood*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D054439:Ghrelin / Q000097:blood; D005934:Glucagon / Q000097:blood; D013006:Growth Hormone / Q000097:blood; D006706:Homeostasis; D006728:Hormones / Q000097:blood*; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D020738:Leptin / Q000097:blood; D008297:Male; D046048:Seals, Earless / Q000097:blood*; D013963:Thyroid Hormones / Q000097:blood; D013997:Time Factors
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D054439:Ghrelin; D006728:Hormones; D007328:Insulin; D020738:Leptin; D013963:Thyroid Hormones; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D005934:Glucagon; D020155:3-Hydroxybutyric Acid; D006854:Hydrocortisone