Bégay V, Valotaire Y, Ravault J P, Collin J P, Falcón J
Laboratoire de Neurobiologie et de Neuroendocrinologie Cellulaires, URA CNRS 290, Poitiers, France.
C R Seances Soc Biol Fil. 1993;187(1):77-86.
Pineal photoreceptor cells produce the neurohormone, melatonin, a major "Zeitgeber" of the organism. This compound has been involved in the control of development, growth, sexual maturation, and seasonal reproductive cycles. We investigated, here, the effects of estradiol-17 beta on melatonin production by cultured pineal photoreceptor cells. Under a light/dark (LD: 12/12) cycle, cultured trout pineal cells maintained a rhythmic secretion of melatonin with higher amounts being released during the dark phase. The amplitude of the rhythm tended to increase with time spent in culture. Application of estradiol-17 beta during the dark phase of a LD cycle (i.e., for 12 h) affected melatonin release in a dose-dependent manner: low concentrations (10(-10) to 10(-8) mol/l) were inhibitory whereas high concentrations (over 10(-7) mol/l) were stimulatory. When estradiol-17 beta was applied continuously for several 24 h LD cycles, the inhibitory effect observed during the first dark phase disappeared later on. Rather, in the presence of estradiol-17 beta, at the concentrations of 10(-9) and 10(-6) mol/l, a high amplitude rhythm in melatonin secretion was recovered faster, when compared to controls. Replacement of 10% fetal calf serum by 0.1% bovine serum albumin did not affect the responses of the photoreceptor cells to 10(-6) mol/l of estradiol-17 beta. The present results bring the first evidence that estradiol-17 beta modulates melatonin secretion by cultured pineal photoreceptors. They further support the idea according to which sexual hormones exert a feedback regulation on the pineal. Pineal photoreceptors appear as multieffector cells which transduce information from, both, physical (photoperiod) and internal (chemical) factors.
松果体光感受器细胞产生神经激素褪黑素，它是生物体主要的“时间信号”。这种化合物参与了发育、生长、性成熟和季节性生殖周期的调控。我们在此研究了17β -雌二醇对培养的松果体光感受器细胞分泌褪黑素的影响。在光/暗（LD：12/12）循环条件下，培养的鳟鱼松果体细胞维持褪黑素的节律性分泌，在暗期释放量更高。节律的幅度随培养时间的延长而趋于增加。在LD循环的暗期（即12小时）应用17β -雌二醇以剂量依赖方式影响褪黑素的释放：低浓度（10^(-10)至10^(-8)摩尔/升）具有抑制作用，而高浓度（超过10^(-7)摩尔/升）具有刺激作用。当连续几个24小时的LD循环持续应用17β -雌二醇时，在第一个暗期观察到的抑制作用随后消失。相反，在17β -雌二醇存在的情况下，与对照组相比，浓度为10^(-9)和10^(-6)摩尔/升时，褪黑素分泌的高幅度节律恢复得更快。用0.1%牛血清白蛋白替代10%胎牛血清不影响光感受器细胞对10^(-6)摩尔/升17β -雌二醇的反应。目前的结果首次证明17β -雌二醇可调节培养的松果体光感受器分泌褪黑素。它们进一步支持了性激素对松果体发挥反馈调节作用的观点。松果体光感受器表现为多效应细胞，可转导来自物理（光周期）和内部（化学）因素的信息。
