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The pineal gland and melatonin 

The pineal gland and melatonin
The pineal gland and melatonin

J. Arendt

, and Timothy M. Cox

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date: 26 February 2021

The pineal gland transduces light–dark cycles for the timing of body rhythms by secretion of melatonin, an endogenous indoleamine derived from tryptophan, the concentrations of which in plasma and cerebrospinal fluid are up to 100 times higher at night than in the daytime. This exerts its effects through transmembrane, G-protein coupled receptors (MT1 and MT2), and nuclear receptors primarily in the suprachiasmatic nucleus, pars tuberalis of the pituitary gland and hypothalamus. The natural period of the human circadian system is on average 24.1 to 24.3 h, and the principal resetting agent is light. Exogenous melatonin can shift the timing of the internal clock to earlier and later times, and synchronize a free-running clock that is not properly entrained to the 24-h day, hence it may have a therapeutic role for disorders of sleep rhythm including jet lag, in shift workers, and in blind people.

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