The Melatonin (MLT), secreted rhythmically by the pineal, is an efferent hormonal signal of the circadian clock. MLT presents overall pleitropic effects but it is the role of MLT as a hormonal circadian signal which is the best documented. MLT-receptors are present in numerous structures/organs and the MLT is now considered as an endogenous synchronizer within the circadian system. The presence of MLT-receptors within the circadian clock, explains that exogenous MLT is a chronobiotic drug. Trials in humans, have confirmed the efficacy of MLT in circadian rhythm disorders. Subtypes of MLT-receptors have been characterized (MT1 and MT2). Striking differences are observed in the distribution pattern of these 2 subtypes. Up to now, MTL-analogues commercialized as drugs, are all non-specific MT1/MT2 agonists acting on the SCN. The development of new specific agonists/antagonists for both subtypes, the identification of the link between MLT target sites within different parts of the brain or the body and the association of specific MLT receptor subtypes and particular physiological effects open great therapeutic potential.

中文翻译：

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褪黑激素：动物研究。

松果体有节奏地分泌的褪黑激素（MLT）是昼夜节律钟发出的激素信号。MLT表现出整体的多效性作用，但MLT作为激素昼夜节律信号的作用已得到最好的记录。MLT受体存在于许多结构/器官中，现在MLT被视为昼夜节律系统中的内源同步器。昼夜节律钟中存在MLT受体，这说明外源性MLT是一种计时生药。在人体中的试验已经证实了MLT在昼夜节律障碍中的功效。已经鉴定了MLT受体的亚型（MT1和MT2）。在这两种亚型的分布模式中观察到惊人的差异。到目前为止，作为药物商业化的MTL类似物都是作用于SCN的非特异性MT1 / MT2激动剂。