Glucocorticoids are commonly associated with responses to stress, but other important functions include homeostatic regulation, energy metabolism and tissue remodeling. At low circulating levels, glucocorticoids bind to high-affinity mineralocorticoid receptors (MR) to activate tissue repair and homeostasis (anabolic pathways), whereas at elevated levels, glucocorticoids bind to glucocorticoid receptors (GR) to activate catabolic pathways. Long distance migrations, such as those performed by Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii), require modification of anatomy, physiology and behavior. Plasma corticosterone (CORT) increases in association with impending departure and flight and may promote muscle-specific anabolic states. To test this idea, we explored glucocorticoid signaling in the pectoralis (flight) and gastrocnemius (leg) muscles of male sparrows on the wintering grounds at three stages leading up to spring departure: winter (February), pre-nuptial molt (March), and pre-departure (April). CORT was detected in plasma and in both muscles, but measures of CORT signaling differed across muscles and stages. Expression of 11β-hydroxysteroid dehydrogenase (11β-HSD) Type 2 (inactivates CORT) increased in the pectoralis at pre-departure, whereas 11β-HSD Type 1 (regenerates CORT) did not change. Neither of the two 11β-HSD isoforms was detectable in the gastrocnemius. Expression of MR, but not GR, was elevated in the pectoralis at pre-departure, while only GR expression was elevated at pre-nuptial molt in gastrocnemius. These data suggest that anabolic functions predominate in the pectoralis only while catabolic activity is undetected in either muscle at pre-departure.

中文翻译：

---

准备迁移的鸣禽骨骼肌中糖皮质激素信号传导的表型灵活性。

糖皮质激素通常与对压力的反应有关，但其他重要功能包括稳态调节，能量代谢和组织重塑。在低循环水平下，糖皮质激素与高亲和性盐皮质激素受体（MR）结合以激活组织修复和体内稳态（合成代谢途径），而在高水平时，糖皮质激素与糖皮质激素受体（GR）结合以激活分解代谢途径。长距离迁移，例如由Gambel的白冠麻雀（Zonotrichia leucophrys gambelii）进行的迁移，需要对解剖学，生理学和行为进行修改。血浆皮质类固醇（CORT）随即将起飞和逃跑而增加，并可能促进特定于肌肉的合成代谢状态。为了验证这个想法，我们在越冬地的雄麻雀的胸肌（飞行）和腓肠肌（腿）肌肉中探索了糖皮质激素信号传导，直至春季出发，分为三个阶段：冬季（二月），婚前蜕皮（三月）和出发前（四月）。在血浆和两块肌肉中都检测到了CORT，但是CORT信号的测量在肌肉和各个阶段都不同。出发前胸膜2型11β-羟类固醇脱氢酶（11β-HSD）的表达增加（使CORT失活），而11β-HSD1型（使CORT再生）的表达没有变化。腓肠肌中两个11β-HSD亚型均未检出。产前胸大肌MR表达升高，而GR升高，腓肠肌婚前蜕皮仅GR表达升高。