Almeida O F, Lincoln G A
Biol Reprod. 1982 Dec;27(5):1062-75. doi: 10.1095/biolreprod27.5.1062.
Adult Soay rams were housed under long days of 16L:8D for 16 weeks, and then exposed to a lighting regimen of either 8L:40D, 8L:28D, 8L:16D or maintained under 16L:8D. The diameter of the testes and the intensity of the sexual skin flush was recorded every 1-2 weeks, while on four occasions during the 8L:40D and 8L:28D regimens the concentrations of melatonin, prolactin and electrolytes (sodium and potassium) were measured in blood samples collected hourly for 2-4 days. During the initial period of 16L:8D, the testes of all rams regressed in size and the sexual skin flush disappeared. In the animals maintained under 16L:8D for more than 16 weeks, the testes began to redevelop spontaneously and there was a reappearance of the skin flush after 23-29 weeks. Compared to this group, the rams switched to 8L:40D and 8L:16D after 16 weeks showed a significant acceleration in testicular development and an earlier skin flush. The rams exposed to 8L:28D failed to show this stimulated response and reactivation of the testes was similar to that under prolonged 16L:8D. During the 16 weeks under 8L:40D there was a 3-fold increase in the 24-h mean plasma concentration of melatonin. A clearly defined 24-h rhythm in the levels of melatonin was evident during the treatment. The rhythm was synchronized in its timing for the different individuals in the group, while the peak levels of melatonin occurred earlier relative to the onset of the light period under 8L:40D compared to 16L:8D. Under the 8L:28D regimen there was an increase in the mean levels of melatonin as for 8L:40D; however, there was no consistent daily rhythm. Exposure to the two photoperiodic regimens also resulted in differences in the plasma profiles of prolactin, while no differences were evident for the levels of electrolytes. The combined results are used to develop a model for the photoperiodic control of the timing of the rhythm in secretion of melatonin is considered of central importance.
成年索艾羊在16小时光照：8小时黑暗的长日照条件下饲养16周，然后分别暴露于8小时光照：40小时黑暗、8小时光照：28小时黑暗、8小时光照：16小时黑暗的光照方案下，或维持在16小时光照：8小时黑暗的条件下。每1 - 2周记录一次睾丸直径和性皮肤潮红的强度，而在8小时光照：40小时黑暗和8小时光照：28小时黑暗方案期间，在4个不同时间点，对每小时采集的血样进行2 - 4天的检测，测量褪黑素、催乳素和电解质（钠和钾）的浓度。在最初的16小时光照：8小时黑暗期间，所有公羊的睾丸体积均缩小，性皮肤潮红消失。在16小时光照：8小时黑暗条件下饲养超过16周的动物中，睾丸开始自发重新发育，23 - 29周后皮肤潮红再次出现。与该组相比，在16周后切换到8小时光照：40小时黑暗和8小时光照：16小时黑暗的公羊，睾丸发育显著加速，皮肤潮红出现得更早。暴露于8小时光照：28小时黑暗的公羊未表现出这种刺激反应，睾丸的重新激活与长时间处于16小时光照：8小时黑暗条件下相似。在8小时光照：40小时黑暗的16周期间，24小时平均血浆褪黑素浓度增加了3倍。在治疗期间，褪黑素水平呈现出明确的24小时节律。该节律在组内不同个体的时间上是同步的，与16小时光照：8小时黑暗相比，8小时光照：40小时黑暗条件下褪黑素的峰值水平相对于光照期开始的时间更早。在8小时光照：28小时黑暗方案下，褪黑素的平均水平与8小时光照：40小时黑暗时一样有所增加；然而，没有一致的每日节律。暴露于这两种光周期方案还导致了催乳素血浆水平的差异，而电解质水平没有明显差异。综合结果用于建立一个光周期控制褪黑素分泌节律时间的模型，褪黑素分泌节律的控制被认为至关重要。
