Meeting Abstract
P2.164 Sunday, Jan. 5 15:30 Corticosteroid Secretion Varies Following Adrenocorticotropic Hormone Stimulation in Northern Elephant Seals CHAMPAGNE, CD*; TIFT, MS; HOUSER, DS; CROCKER, DE; National Marine Mammal Foundation; Sonoma State University; National Marine Mammal Foundation; Sonoma State University cory.champagn@gmail.com
During molting, northern elephant seals exhibit substantial alterations in circulating cortisol concentrations, probably to facilitate pelage synthesis while fasting. How these changes influence the hypothalamic-pituitary-adrenal (HPA) axis and the stress response, however, is not known. To investigate the modulation of the HPA axis during molting, we administered ACTH (25 units, intramuscularly) to sixteen juvenile elephant seals at the beginning (n=6), middle (n=5), and end (n=5) of their spring molting period in a cross-sectional study design. Blood samples were collected immediately before, and then periodically for 2.5 hrs after, ACTH administration. We quantified circulating concentrations of ACTH, and the responses of cortisol and aldosterone. Both cortisol and aldosterone concentrations markedly increased following stimulation by ACTH and remained elevated for the duration of sampling. There were no detectable differences in the magnitude of cortisol response to ACTH administration among the study groups (F = 0.9, p = 0.4) whereas aldosterone showed a more variable response, with the greatest total secretion occurring in the middle of the molting period (F = 4.7, p = 0.03). ACTH is not a strong aldosterone secretagogue in terrestrial mammals but several studies have measured increased aldosterone after ACTH stimulation in marine mammals, indicating its potential importance in osmoregulation during stress in these species. Cortisol and aldosterone increased in parallel following ACTH stimulation, and the slope of this relationship varied among the study groups. This suggests that the release of these hormones is closely coupled in this species and possibly other marine mammals.
