Abstract
Levels of melatonin in mammalian circulation are well documented; however, its levels in tissues and other body fluids are yet only poorly established. It is obvious that melatonin concentrations in cerebrospinal fluid (CSF) of mammals including humans are substantially higher than those in the peripheral circulation. Evidence indicates that melatonin produced in pineal gland is directly released into third ventricle via the pineal recess. In addition, brain tissue is equipped with the synthetic machinery for melatonin production and the astrocytes and glial cells have been proven to produce melatonin. These two sources of melatonin may be responsible for its high levels in CNS. The physiological significance of the high levels of melatonin in CNS presumably is to protect neurons and glia from oxidative stress. Melatonin as a potent antioxidant has been reported to be a neuroprotector in animals and in clinical studies. It seems that long term melatonin administration which elevates CSF melatonin concentrations will retard the progression of neurodegenerative disorders, for example, Alzheimer disease.
Highlights
Melatonin is a secretory product of pineal gland in mammals and it is synthesized by pinealocytes beginning with the essential amino acid, tryptophan
It has been speculated that melatonin of extrapineal origin is consumed by the tissues or organs where melatonin is produced as a defense against the oxidative stress [69]
Based on the findings reported by Rizzo et al [53], the free melatonin only comprised one fourth of the total melatonin in the cerebrospinal fluid (CSF)
Summary
Melatonin is a secretory product of pineal gland in mammals and it is synthesized by pinealocytes beginning with the essential amino acid, tryptophan. The blood values range from several pg/ml during the day to more than 50 pg/ml at its nighttime peak These levels, do not reflect the real concentrations of melatonin in tissues or in other body fluids. A clinical study has recently reported that melatonin concentrations in third ventricle of patients with movement disorders are significantly higher than in lateral ventricles and in blood. When CSF is obtained via the lumbar puncture, which is often the case, melatonin levels would be expected to be significantly lower than CSF collected from the ventricles of the brain. Even in the single case where CSF via lumbar punctured was collected at night, the patient was in light at the time Under these conditions, melatonin levels are either at their basal values or in the process of degradation.
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