Abstract

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Discussion
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Some of the best correlative evidence concerning an endogenous role for melatonin in human sleep comes from studies in free running blind or sighted subjects when maximum sleep propensity occurs closely associated with the peak of melatonin secretion and the trough of core temperature. Melatonin can affect sleep as a soporific and as a phase shifter and it modifies the EEG. There is still inconsistency in the findings however and some studies have found few effects of importance on sleep. Following an acute dose of melatonin (0.5 -10 mg) core body temperature declines (dose dependently) and causal links have been suggested between this effect and the induction of sleepiness (both effects are posture dependent). Melatonin (0.5 mg - 5mg) phase advances and delays the circadian system (endogenous melatonin, core temperature, sleep timing) according to a PRC (phase response curve). However it has proved impossible so far to demonstrate convincingly entrainment of strongly endogenous rhythms in humans, with the exception of stabilisation of the sleep wake cycle to 24 hours in both blind and sighted subjects. Recent data suggests that the effects of melatonin can be complex and variable, indeed fragmentation of sleep has been seen in a dim light environment. The majority of published data indicate that melatonin has therapeutic benefits in circadian rhythm-related sleep disorders. However many questions remain and much further research is needed on its physiological role and pharmacological effects in humans. It is likely that endogenous melatonin indicates dark onset (the rise) and offset (the decline) and reinforces physiological functions associated with darkness in humans as in other mammals.

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Presentation Number SAarendt0880
Keywords: melatonin, rhythm, human, blind