Arendt J, Symons A M, English J, Poulton A L, Tobler I
Department of Biochemistry, University of Surrey, Guildford, U.K.
Reprod Nutr Dev (1980). 1988;28(2B):387-97. doi: 10.1051/rnd:19880305.
The pineal gland is essential for the perception of photoperiod change in many species. Information about photoperiod length is conveyed through pineal secretion of the methoxyindole melatonin. Melatonin, suitably administered in physiological quantities is equipotent with artificial photoperiod in the induction of photoperiodic responses. Most experimental work suggests that it is the duration of high night time melatonin secretion (positively correlated with the length of the natural or artificial dark phase) which conveys the photoperiodic signal. Continuous release implants induce short day effects in ewes, entirely comparable to daily feeding of melatonin or short photoperiod. A minimum duration of secretion rather than a specific duration is therefore probably critical to short day effects. There appears to be a seasonal variation in sensitivity to short day melatonin effects (induction of early oestrus) which can be shifted to an earlier time of year following one oestrus advance the previous year. Short duration melatonin is read as a long day even secreted with 22 hour periodicity, suggesting a lack of circadian variation in sensitivity to melatonin.
松果体对于许多物种感知光周期变化至关重要。光周期长度的信息通过松果体分泌的甲氧基吲哚褪黑素传递。以生理量适当施用的褪黑素在诱导光周期反应方面与人工光周期等效。大多数实验工作表明，是夜间高褪黑素分泌的持续时间（与自然或人工黑暗期的长度呈正相关）传递了光周期信号。持续释放植入物在母羊中诱导短日照效应，与每日投喂褪黑素或短光周期完全可比。因此，分泌的最短持续时间而非特定持续时间可能对短日照效应至关重要。对短日照褪黑素效应（诱导早期发情）的敏感性似乎存在季节性变化，在前一年发情提前一次后，这种变化可以转移到一年中更早的时间。即使以22小时周期分泌，短持续时间的褪黑素也被视为长日照，这表明对褪黑素的敏感性缺乏昼夜节律变化。
