Guerin M V, Deed J R, Kennaway D J, Matthews C D
Department of Obstetrics and Gynaecology, University of Adelaide, Australia.
J Pineal Res. 1995 Aug;19(1):7-15. doi: 10.1111/j.1600-079x.1995.tb00165.x.
Plasma melatonin was measured at the winter and summer solstices and the autumn and spring equinoxes in four mares held under natural conditions at 35 degrees S. At all seasons the onset of the nightly elevated melatonin was coincident with or after the time of sunset and the melatonin offset after the time of sunrise. The duration of elevated melatonin was not different from the duration of natural scotophase for each season, with the duration of elevated melatonin longer in winter than the other seasons. Immediately following each 24 hr sampling two mares were resampled in acutely extended darkness to determine the melatonin profile of the endogenous rhythm of the circadian pacemaker, originating from the suprachiasmatic nuclei (SCN). At each season melatonin secretion commenced earlier and decreased later than that measured under the natural photoperiodic condition, suggesting that the expression of the melatonin rhythm is normally gated by natural environmental light both at dusk and dawn. The interval from the onset of melatonin measured under acutely extended darkness to the time of sunset was greater in the spring/summer than the autumn/winter suggesting a possible alternating signal throughout the year. Thus the mare appears to exhibit a similar interaction between endogenous circadian rhythmic activity and the natural photoperiod as the ewe which may underlie the mechanism for timing reproductive activity through the year.
在南纬35度自然条件下饲养的四匹母马中，于冬至、夏至、秋分和春分测量血浆褪黑素。在所有季节，夜间褪黑素升高的开始时间与日落时间一致或在日落时间之后，褪黑素水平下降时间在日出时间之后。每个季节褪黑素升高的持续时间与自然暗期的持续时间没有差异，其中冬季褪黑素升高的持续时间比其他季节更长。在每24小时采样后，立即对两匹母马在急性延长黑暗条件下重新采样，以确定源自视交叉上核（SCN）的昼夜节律起搏器内源性节律的褪黑素谱。在每个季节，褪黑素分泌开始时间比在自然光周期条件下测量的时间更早，结束时间更晚，这表明褪黑素节律的表达通常在黄昏和黎明时受自然环境光的调节。在急性延长黑暗条件下测量的褪黑素开始时间到日落时间的间隔在春夏季比秋冬季更大，这表明全年可能存在交替信号。因此，母马似乎表现出与母羊在内源性昼夜节律活动和自然光周期之间类似的相互作用，这可能是全年生殖活动定时机制的基础。
