McMillen I C, Houghton D C, Young I R
Department of Physiology, University of Adelaide, South Australia.
J Reprod Fertil Suppl. 1995;49:137-46.
We have investigated whether the maternal melatonin rhythm provides the fetus with either a circadian or seasonal 'signal' during development. Our findings provide evidence that melatonin can generate and entrain the early evening peak in the daily rhythm of fetal breathing movements. In contrast, daily variations in maternal and fetal prolactin concentrations are present in pinealectomized ewes, are altered by changes in the time of onset of darkness, but are unaltered by changes in the phase of the daily melatonin rhythm. The mechanisms that generate and control the daily prolactin rhythm before and after birth are therefore unknown. It is clear from a number of studies that the duration of the nocturnal melatonin signal provides the adult and fetal sheep with photoperiodic information. We investigated whether there are differences in the fetal plasma concentrations of prolactin in ewes held in long and short photoperiods after surgical disconnection of the fetal hypothalamus and pituitary and demonstrated that there was a fetal prolactin response to the external photoperiod in sheep fetuses in which the hypothalamo-pituitary axis was either intact or surgically disconnected. We have suggested that one potential extrahypothalamic site of action of maternal melatonin is at the pars tuberalis of the fetal pituitary. It appears therefore that there are a number of different mechanisms for the neuroendocrine transmission of information about the time of day and duration of the external photoperiod to the sheep fetus throughout late gestation.
我们研究了母体褪黑素节律在胎儿发育过程中是否为其提供昼夜节律或季节性“信号”。我们的研究结果表明，褪黑素能够产生并调节胎儿呼吸运动每日节律中的傍晚高峰。相比之下，松果体切除的母羊中母体和胎儿催乳素浓度存在每日变化，这些变化会因黑暗开始时间的改变而改变，但不会因每日褪黑素节律相位的改变而改变。因此，出生前后产生和控制每日催乳素节律的机制尚不清楚。从多项研究中可以清楚地看出，夜间褪黑素信号的持续时间为成年和胎儿绵羊提供了光周期信息。我们研究了在手术切断胎儿下丘脑和垂体后，处于长光照周期和短光照周期的母羊中胎儿血浆催乳素浓度是否存在差异，并证明在胎儿下丘脑 - 垂体轴完整或手术切断的绵羊胎儿中，胎儿催乳素对外部光周期有反应。我们认为母体褪黑素一个潜在的下丘脑外作用位点是在胎儿垂体的结节部。因此，在整个妊娠后期，似乎存在多种不同的机制将有关一天中的时间和外部光周期持续时间的信息神经内分泌传递给绵羊胎儿。
