Karsch F J, Malpaux B, Wayne N L, Robinson J E
Reproductive Endocrinology Program, University of Michigan, Ann Arbor 48109-0404.
Reprod Nutr Dev (1980). 1988;28(2B):459-72. doi: 10.1051/rnd:19880311.
The following is a progress report of our studies to identify important features of the circadian pattern of melatonin secretion which provide the photoperiodic code for daylength in regulating seasonal breeding in the Suffolk ewe. The first series of experiments evaluated two conceptual models of how melatonin codes for daylength: the circadian timing of the melatonin elevation as opposed to the length of the time melatonin is elevated during each 24-hr period (phase vs duration). Strong support has been gathered for the duration hypothesis. No evidence was obtained to support a role for phase; nevertheless, this hypothesis could not be discounted definitively. A second series of studies evaluated the importance of the previous melatonin pattern to the interpretation of a given melatonin signal. Evidence is presented that a fixed melatonin pattern can maintain a given reproductive response only for a limited length of time and that this response can be prolonged by appropriate changes in the melatonin pattern. Thus, change is an important feature of the melatonin signal. Further, the nature of the melatonin change appears to be crucial, specifically whether the nocturnal elevation increases or decreases in duration. Thus, transfer to a common photoperiod can promote either reproductive induction or arrest, depending upon whether the transfer leads to a decrease or increase in daylength. This has important ramifications to the photoperiodic timekeeping process in those species of mammals which utilize daylength to time their seasonal reproductive cycle.
以下是我们的研究进展报告，旨在确定褪黑素分泌昼夜节律模式的重要特征，这些特征为萨福克母羊调节季节性繁殖的日长提供光周期编码。第一系列实验评估了褪黑素如何编码日长的两种概念模型：褪黑素升高的昼夜节律时间与每个24小时周期内褪黑素升高的时间长度（相位与持续时间）。已经收集到了对持续时间假说的有力支持。没有获得支持相位作用的证据；然而，这一假说不能被明确排除。第二系列研究评估了先前的褪黑素模式对解释给定褪黑素信号的重要性。有证据表明，固定的褪黑素模式只能在有限的时间内维持给定的生殖反应，并且这种反应可以通过褪黑素模式的适当改变而延长。因此，变化是褪黑素信号的一个重要特征。此外，褪黑素变化的性质似乎至关重要，特别是夜间升高的持续时间是增加还是减少。因此，转移到共同的光周期可以促进生殖诱导或生殖停滞，这取决于转移导致日长减少还是增加。这对那些利用日长来安排季节性繁殖周期的哺乳动物物种的光周期计时过程具有重要影响。
