Guerin M V, Napier A J, Matthews C D
Department of Obstetrics and Gynaecology, University of Adelaide, Queen Elizabeth Hospital, Woodville, South Australia.
J Reprod Fertil. 1994 May;101(1):145-50. doi: 10.1530/jrf.0.1010145.
Groups of Romney Marsh ewes (n = 24) were injected with exogenous melatonin or subjected to extended darkness or a combination of both at dusk from the winter to the summer solstice before being re-exposed to the natural photoperiod at 35 degrees S. The animals were at all times exposed to natural dawn. The onset of subsequent oestrus was delayed when compared with controls subjected to the natural photoperiod. Either melatonin or darkness or a combination were equally effective at delaying oestrus. The results are consistent with a hypothesis based on an external coincidence model of seasonal breeding involving the coincidence of a light-sensitive phase set close to dusk that, when exposed to light in spring and summer, prepares the reproductive axis to respond correctly to the direct effects of the inductive photoperoid in autumn. The offset of the time of oestrus was not affected by the experimental treatments nor was the timing of the subsequent reproductive season. Since melatonin was as effective as darkness at influencing the assumed photosensitive signal, even in the presence of natural light, melatonin may act through the light reception system.
在南纬35度处，从冬季到夏至，将罗姆尼沼泽母羊分成若干组（每组n = 24只），在黄昏时给它们注射外源性褪黑素，或使其处于延长的黑暗环境中，或二者结合，之后再使其重新暴露于自然光周期下。这些动物始终能见到自然的黎明。与处于自然光周期下的对照组相比，后续发情的开始时间延迟了。单独使用褪黑素、黑暗环境或二者结合在延迟发情方面效果相同。这些结果与基于季节性繁殖的外部巧合模型的假设一致，该模型涉及一个接近黄昏时设定的光敏感阶段，当在春季和夏季暴露于光照下时，该阶段会使生殖轴做好准备，以便在秋季对诱导光周期的直接影响做出正确反应。发情时间的偏移不受实验处理的影响，后续繁殖季节的时间安排也不受影响。由于即使在有自然光的情况下，褪黑素在影响假定的光敏感信号方面与黑暗环境效果相同，因此褪黑素可能是通过光接收系统起作用的。
