Ensminger David C, Somo Derek A, Houser Dorian S, Crocker Daniel E
Dept. of Biology, Sonoma State University, 1801 E. Cotati Ave., Rohnert Park, CA 94928, USA.
Dept. of Biology, Sonoma State University, 1801 E. Cotati Ave., Rohnert Park, CA 94928, USA.
Gen Comp Endocrinol. 2014 Aug 1;204:150-7. doi: 10.1016/j.ygcen.2014.04.024. Epub 2014 May 2.
Strong individual and life-history variation in serum glucocorticoids has been documented in many wildlife species. Less is known about variation in hypothalamic-pituitary-adrenal (HPA) axis responsiveness and its impact on metabolism. We challenged 18 free-ranging adult male northern elephant seals (NES) with an intramuscular injection of slow-release adrenocorticotropic hormone (ACTH) over 3 sample periods: early in the breeding season, after 70+ days of the breeding fast, and during peak molt. Subjects were blood sampled every 30 min for 2h post-injection. Breeding animals were recaptured and sampled at 48 h. In response to the ACTH injection, cortisol increased 4-6-fold in all groups, and remained elevated at 48 h in early breeding subjects. ACTH was a strong secretagogue for aldosterone, causing a 3-8-fold increase in concentration. Cortisol and aldosterone responses did not vary between groups but were correlated within individuals. The ACTH challenge produced elevations in plasma glucose during late breeding and molting, suppressed testosterone and thyroid hormone at 48 h in early breeding, and increased plasma non-esterified fatty acids and ketoacids during molting. These data suggest that sensitivity of the HPA axis is maintained but the metabolic impacts of cortisol and feedback inhibition of the axis vary with life history stage. Strong impacts on testosterone and thyroid hormone suggest the importance of maintaining low cortisol levels during the breeding fast. These data suggest that metabolic adaptations to extended fasting in NES include alterations in tissue responses to hormones that mitigate deleterious impacts of acute or moderately sustained stress responses.
许多野生动物物种的血清糖皮质激素存在显著的个体差异和生活史差异。关于下丘脑 - 垂体 - 肾上腺（HPA）轴反应性的变化及其对新陈代谢的影响，我们了解得较少。我们在三个采样期对18只自由放养的成年雄性北象海豹（NES）进行了肌肉注射缓释促肾上腺皮质激素（ACTH）的挑战：繁殖季节早期、繁殖期禁食70多天后以及换毛高峰期。注射后每30分钟对受试者进行一次血样采集，持续2小时。在48小时时对繁殖期动物进行重新捕获并采样。对ACTH注射的反应中，所有组的皮质醇增加了4 - 6倍，并且在繁殖早期的受试者中48小时时仍保持升高。ACTH是醛固酮的强效促分泌剂，导致其浓度增加3 - 8倍。皮质醇和醛固酮反应在组间没有差异，但在个体内相关。ACTH刺激在繁殖后期和换毛期导致血浆葡萄糖升高，在繁殖早期48小时时抑制睾酮和甲状腺激素，并在换毛期增加血浆非酯化脂肪酸和酮酸。这些数据表明HPA轴的敏感性得以维持，但皮质醇的代谢影响和该轴的反馈抑制随生活史阶段而变化。对睾酮和甲状腺激素的强烈影响表明在繁殖期禁食期间维持低皮质醇水平的重要性。这些数据表明，NES对延长禁食的代谢适应包括组织对激素反应的改变，从而减轻急性或中度持续应激反应的有害影响。
