Cockrem J F
Ecology Division, Department of Scientific and Industrial Research, Lower Hutt, New Zealand.
J Pineal Res. 1991 Jan;10(1):2-8. doi: 10.1111/j.1600-079x.1991.tb00002.x.
Circadian rhythms of melatonin secretion in birds are influenced by daylength and light intensity. Daily patterns of melatonin secretion were examined in Adelie penguins (Pygoscelis adeliae) under natural continuous daylight at Cape Bird, Antarctica (77 degrees S). Although daylight is continuous during the Antarctic summer there was a marked daily cycle of light intensity. However, there was no relationship between mean plasma melatonin levels and time of day in groups of 2-10 penguins sampled at 2-3 h intervals in November, December, or January. Mean melatonin levels over 24 h in groups of birds from which single samples were collected, or in groups of birds sampled repeatedly through cannulae, were low (12.4 +/- 1.2 pg/ml-28.8 +/- 4.4 pg/ml for 4 sampling periods; n = 22-163). Levels in individual birds were, however, quite variable and ranged from 5.0-68.1 pg/ml. Some birds had periods of increased melatonin levels that tended to occur during the time of day when light intensity was least. One bird had a clear low amplitude melatonin rhythm with a peak during the time of least light intensity. These results, the first for any bird under a natural photoperiod, indicate that melatonin secretion is inhibited by natural continuous daylight, but that it is not abolished.
鸟类褪黑素分泌的昼夜节律受日照长度和光照强度影响。在南极洲伯德角（南纬77度）自然持续日照条件下，对阿德利企鹅（Pygoscelis adeliae）的褪黑素分泌日模式进行了研究。尽管南极夏季日照持续，但光照强度存在明显的日周期。然而，在11月、12月或1月，以2 - 3小时为间隔对2 - 10只企鹅进行采样，其血浆褪黑素平均水平与一天中的时间并无关联。对采集单个样本的鸟类群体，或通过插管反复采样的鸟类群体，其24小时内的褪黑素平均水平较低（4个采样期为12.4±1.2 pg/ml - 28.8±4.4 pg/ml；n = 22 - 163）。然而，个体鸟类的水平差异很大，范围在5.0 - 68.1 pg/ml之间。一些鸟类的褪黑素水平升高期往往出现在光照强度最低的时段。有一只鸟呈现出明显的低振幅褪黑素节律，在光照强度最低时达到峰值。这些结果是首次在自然光周期下对任何鸟类进行研究所得，表明自然持续日照会抑制褪黑素分泌，但并非完全消除。
