Gower B A, Nagy T R, Stetson M H
School of Life and Health Sciences, University of Delaware, Newark 19716, USA.
Gen Comp Endocrinol. 1996 Jan;101(1):53-62. doi: 10.1006/gcen.1996.0007.
Collared lemmings (Dicrostonyx groenlandicus) of both sexes show seasonal changes in body mass and body composition. Previous studies using single-point sampling indicated that, in young males, these photoperiod-mediated changes are associated with changes in circulating growth hormone (GH), corticosterone (B), and thyroid hormones. The present study was conducted to (1) examine daily fluctuations in serum levels of GH, B, and thyroxine (T4) in animals exposed to long (22L:2D, "LD"), intermediate (16L:8D, "ID"), and short (8L:16D, "SD") photoperiods, (2) confirm that conclusions based on single-point sampling are valid when photoperiod-related differences in hormone concentration are examined over 24 hr, (3) examine the effect of photoperiod on hormone concentrations in adults of both sexes, and (4) characterize the daily pineal melatonin rhythm in this species. Adult male and female collared lemmings housed in SD had higher levels of GH, and lower levels of B and T4, even when the diurnal variations in serum concentrations of these hormones were taken into account. A significant effect of time was observed on serum B (ID animals only) and serum T4. ID lemmings had B levels that were similar to those of SD animals, but concentrations of GH that more closely resembled those of LD animals. Females had lower GH and T4 than males. Pineal melatonin concentration closely tracked the dark phase of the day in each of the three photoperiods. Photoperiod-mediated changes in melatonin synthesis may mediate observed day length-related differences in serum concentrations of metabolic hormones, which in turn may contribute to the seasonal changes in body composition observed in collared lemmings.
环颈旅鼠（Dicrostonyx groenlandicus）无论雌雄，其体重和身体组成都会随季节变化。以往使用单点采样的研究表明，在年轻雄性旅鼠中，这些由光周期介导的变化与循环生长激素（GH）、皮质酮（B）和甲状腺激素的变化有关。本研究旨在：（1）检测暴露于长光周期（22小时光照：2小时黑暗，“LD”）、中间光周期（16小时光照：8小时黑暗，“ID”）和短光周期（8小时光照：16小时黑暗，“SD”）的动物血清中GH、B和甲状腺素（T4）水平的每日波动情况；（2）当在24小时内检测与光周期相关的激素浓度差异时，确认基于单点采样得出的结论是否有效；（3）研究光周期对成年雌雄旅鼠激素浓度的影响；（4）描绘该物种松果体褪黑素的每日节律。即使考虑到这些激素血清浓度的昼夜变化，饲养在短光周期环境中的成年雌雄环颈旅鼠的GH水平较高，而B和T4水平较低。观察到时间对血清B（仅中间光周期的动物）和血清T4有显著影响。中间光周期的旅鼠B水平与短光周期动物相似，但GH浓度更接近长光周期动物。雌性旅鼠的GH和T4水平低于雄性。在三个光周期中的每一个，松果体褪黑素浓度都紧密跟踪一天中的黑暗阶段。光周期介导的褪黑素合成变化可能介导了观察到的与日照长度相关的代谢激素血清浓度差异，这反过来可能导致环颈旅鼠身体组成的季节性变化。
