Endogenous Melatonin is the hormone naturally produced and secreted primarily by the pineal gland in the brain, playing a critical role as the body’s principal regulator of the circadian rhythm. This indoleamine hormone signals the onset of biological night, thereby facilitating the initiation and maintenance of sleep. It is an essential component of the neuroendocrine system, linking environmental light cues to the body’s internal timing mechanisms. The level of endogenous melatonin is a crucial biomarker for assessing circadian health.
Origin
The term combines endogenous, which means originating from within an organism, with melatonin, a compound first isolated and chemically characterized in the 1950s. The name melatonin was coined due to its initial observed effect on melanophores, or pigment cells, in amphibians. Its role as the “darkness hormone” in humans was subsequently established through decades of chronobiology research.
Mechanism
The synthesis and release of endogenous melatonin are directly controlled by the light-dark cycle perceived by the retina, which sends signals to the suprachiasmatic nucleus (SCN), the body’s master clock. As darkness falls, the SCN disinhibits the pineal gland, leading to a dramatic increase in the conversion of serotonin into melatonin. This nocturnal surge then binds to MT1 and MT2 receptors in the SCN, modulating core body temperature and promoting the necessary physiological state for sleep.
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