Boonstra R, Singleton G R
Division of Life Sciences, University of Toronto, Ontario, Canada.
Gen Comp Endocrinol. 1993 Aug;91(2):126-43. doi: 10.1006/gcen.1993.1113.
Every 10 years snowshoe hare populations across the boreal forest of North America go through a population cycle, culminating in a decline lasting 4 or more years. We tested the hypothesis that snowshoe hares during the decline are in poor condition and less able to respond to challenges in their environment by examining the stress response of male hares. Three groups from February and May, 1991 (the second year of the hare decline in the Yukon), were compared: baseline hares were collected to obtain resting hormone levels; control hares were wild animals caught at randomly placed sites; and fed hares were wild animals caught on supplementary fed areas. The latter two groups were sequentially bled to examine their response to dexamethasone (DEX) followed by adrenocorticotropic hormone (ACTH). Trapping and handling were stressful to the experimental hares as the initial blood levels of total and free cortisol levels were higher (especially in controls), testosterone levels were lower, and glucose levels were higher in experimental hares than in baseline hares. Control and fed hares showed similar total and free cortisol responses, falling to low levels after the DEX injection and increasing rapidly in response to the ACTH injection. However, control hares were in worse condition than fed hares as indicated by the higher free cortisol levels and lower maximum corticosteroid-binding capacity (MCBC) in control hares. In addition, though testosterone levels fell in both groups in response to DEX, only the fed hares showed a large, transitory increase 30 min after the ACTH injection. An unexpected finding was a dramatic increase in MCBC levels 30 min after the ACTH injection in both experimental groups, but it was more pronounced in the fed group. We conclude that the pituitary-adrenocortical feedback system in hares from declining populations is operating normally and that they should be able to cope with acute, short-term stressors, but that they are in poor condition and are exposed to higher levels of free cortisol than fed hares in good condition.
在北美洲北方森林地区，雪兔种群数量每10年经历一次周期变化，最终会出现持续4年或更长时间的数量下降。我们通过研究雄性雪兔的应激反应，来验证这样一个假设：数量下降阶段的雪兔身体状况不佳，应对环境挑战的能力较弱。我们比较了1991年2月和5月（育空地区雪兔数量下降的第二年）的三组雪兔：采集基线雪兔以获取其静息激素水平；对照雪兔是在随机地点捕获的野生动物；投喂雪兔是在有补充食物区域捕获的野生动物。后两组雪兔依次接受采血，以检测它们对地塞米松（DEX）和促肾上腺皮质激素（ACTH）的反应。诱捕和处理对实验雪兔来说是有压力的，因为实验雪兔的总皮质醇和游离皮质醇的初始血液水平更高（尤其是对照组），睾酮水平更低，血糖水平比基线雪兔更高。对照雪兔和投喂雪兔的总皮质醇和游离皮质醇反应相似，注射DEX后降至低水平，注射ACTH后迅速升高。然而，对照雪兔的状况比投喂雪兔更差，这体现在对照雪兔的游离皮质醇水平更高，最大皮质类固醇结合能力（MCBC）更低。此外，虽然两组雪兔的睾酮水平在注射DEX后都下降了，但只有投喂雪兔在注射ACTH后30分钟出现了大幅的、短暂的升高。一个意外发现是，两组实验组在注射ACTH后30分钟，MCBC水平都急剧上升，但在投喂组中更为明显。我们得出结论，数量下降种群中的雪兔垂体 - 肾上腺皮质反馈系统运作正常，它们应该能够应对急性短期应激源，但它们身体状况不佳，与状况良好的投喂雪兔相比，暴露于更高水平的游离皮质醇中。
