Gündüz B, Stetson M H
Department of Biological Sciences, University of Delaware, Newark 19716, USA.
J Pineal Res. 2001 Jan;30(1):56-64. doi: 10.1034/j.1600-079x.2001.300108.x.
In a previous paper we demonstrated that properly timed 1-hr infusions of 50 ng melatonin effectively suppressed testicular development in juvenile Siberian hamsters. Only melatonin infused between 20:00 and 21:00 hr was effective in animals exposed to 16L (lights off 20:00 hr). In this paper we further investigate the importance of the coincidence and duration hypotheses of daily exposure of melatonin. Prepubertal Siberian hamsters received either 4- or 8-hr melatonin infusions at various times either on long photoperiod (LD 16:8 = 16L) or on short photoperiod (LD 10:14 = 10L). Daily 8-hr melatonin infusions suppressed testicular development in both photoperiods. Daily 4-hr, 50 ng/hr, melatonin infusions at 17:00-21:00 hr inhibited testicular growth in 16L and daily 4-hr melatonin infusions (either 50 ng/h or 50 ng/day) inhibited testicular growth at 17:00-21:00 hr in 10L. We also tested the efficacy of an interrupted melatonin infusion of long duration (8 hr). Pinealectomized prepubertal male Siberian hamsters, born on 16L, were infused with two signals of 4 hr separated by an interval of 2 hr. Melatonin-infused groups had significantly inhibited testicular growth compared to vehicle-infused animals. Testicular development was maximally inhibited only in those groups in which the period of melatonin sensitivity identified in the previous paper (20:00-21:00 hr) overlapped or immediately followed a period of melatonin infusion. Considering the restrictions of the experimental design employed in these studies, the results are best explained by the hypothesis that the photoperiodic gonadal response in juvenile Siberian hamsters is regulated by the coincidence in time of exogenously administered melatonin with an intrinsic rhythm of sensitivity to melatonin, which occurred at 20:00-21:00 hr. The duration of the melatonin signal alone can not explain the results.
在之前的一篇论文中，我们证明，在幼年西伯利亚仓鼠中，适时进行1小时、50纳克褪黑素的输注能有效抑制睾丸发育。只有在20:00至21:00之间输注褪黑素，对处于16L光照周期（20:00熄灯）的动物才有效。在本文中，我们进一步研究了褪黑素每日暴露的同步性和持续时间假说的重要性。青春期前的西伯利亚仓鼠在长光照周期（LD 16:8 = 16L）或短光照周期（LD 10:14 = 10L）的不同时间接受4小时或8小时的褪黑素输注。每日8小时的褪黑素输注在两个光照周期中均抑制了睾丸发育。在16L光照周期下，每日17:00至21:00进行4小时、50纳克/小时的褪黑素输注抑制了睾丸生长；在10L光照周期下，每日17:00至21:00进行4小时的褪黑素输注（50纳克/小时或50纳克/天）抑制了睾丸生长。我们还测试了长时间（8小时）间断输注褪黑素的效果。出生在16L光照周期的去松果体青春期前雄性西伯利亚仓鼠，接受了两个时长为4小时、间隔2小时的信号输注。与输注赋形剂的动物相比，输注褪黑素的组睾丸生长受到显著抑制。只有在先前论文中确定的褪黑素敏感时间段（20:00至21:00）与褪黑素输注时间段重叠或紧随其后的那些组中，睾丸发育才受到最大程度的抑制。考虑到这些研究中所采用实验设计的局限性，这些结果最好用以下假说解释：幼年西伯利亚仓鼠的光周期性腺反应是由外源性给予的褪黑素与对褪黑素的内在敏感节律在时间上的同步性所调节的，这种同步性发生在20:00至21:00。仅褪黑素信号的持续时间无法解释这些结果。
