Matthews C D, Seamark R F, Guerin M V
Department of Obstetrics and Gynaecology, University of Adelaide, Queen Elizabeth Hospital, Woodville, South Australia.
J Reprod Fertil. 1992 Aug;95(3):869-75. doi: 10.1530/jrf.0.0950869.
Plasma melatonin was measured at the summer and winter solstices and the autumn and spring equinoxes in Romney Marsh sheep held under natural conditions in South Australia (35 degrees S). The amount of melatonin detected was generally related to the extent of natural darkness, though the melatonin onset was particularly delayed after dusk in winter compared with other seasons. The duration of detectable melatonin was shorter in summer than at any other season. After each initial 24 h sampling, the sheep were resampled for a further 24 h in acutely extended darkness to mark the phase and duration of suprachiasmatic nuclei activity which is believed to be the source of the melatonin signal. The onset of high plasma melatonin was earlier than the time of natural sunset in spring and summer, but not different from the time of natural sunset in autumn and winter. The offset of high plasma melatonin was later than the time of natural sunrise at all times of year and particularly so in summer. Under the extended dark conditions, the duration of detectable melatonin was longer than that under natural photoperiod at all seasons of the year and the duration of melatonin was again shorter in summer than winter. If melatonin measurements under the conditions of extended darkness do reflect the phase and duration of suprachiasmatic nuclei function then the natural light of the photoperiod can, particularly during long photoperiod conditions, mask the expression of the pacemaker. The findings may have implications for the timing of the breeding season in Romney Marsh sheep.
在南澳大利亚（南纬35度）自然条件下饲养的罗姆尼沼泽羊中，于夏至、冬至以及春秋分测量了血浆褪黑素水平。检测到的褪黑素量一般与自然黑暗程度相关，不过与其他季节相比，冬季黄昏后褪黑素开始分泌的时间特别延迟。夏季可检测到的褪黑素持续时间比其他任何季节都短。在每次最初的24小时采样后，让绵羊在急性延长的黑暗环境中再采样24小时，以标记视交叉上核活动的阶段和持续时间，视交叉上核被认为是褪黑素信号的来源。春季和夏季血浆褪黑素水平升高的开始时间早于自然日落时间，但与秋季和冬季的自然日落时间无差异。一年中任何时候血浆褪黑素水平升高的结束时间都晚于自然日出时间，夏季尤其如此。在延长黑暗条件下，一年中所有季节可检测到的褪黑素持续时间都比自然光周期下长，且夏季褪黑素持续时间再次短于冬季。如果在延长黑暗条件下的褪黑素测量确实反映了视交叉上核功能的阶段和持续时间，那么光周期的自然光，尤其是在长光周期条件下，可能会掩盖起搏器的表达。这些发现可能对罗姆尼沼泽羊繁殖季节的时间安排有影响。
