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PubMedDate not supplied

Chronome assessment of circulating melatonin in humans.

BACKGROUND: Melatonin (MEL) production occurs mainly during the dark span. A prominent circadian variation is demonstrated in both blood and urine in humans. MATERIALS AND METHODS: The circadian, circannual, age and gender patterns of MEL were concomitantly investigated in 40 men and 132 women, each providing blood samples every 4 hours for 24 hours for conventional and cosinor analysis. RESULTS: Circulating MEL is circadian periodic (P < 0.001), peaking at night. The MESOR (rhythm-adjusted mean) is higher in women than in men. The circadian amplitude decreases with age. Both are modulated by a circannual variation, the MESOR peaking in winter (P < 0.001) and the circadian amplitude in summer (P < 0.05). CONCLUSIONS: Samples, unqualified as to gender, age and/or season, incompletely characterize the circadian MEL patterns. This chronome approach detects changes that may escape detection otherwise, checking whether a value is too high or too low, and also whether "swinging" occurs to the right extent.

Adult↗

PubMedDate not supplied

[Melatonin and seasonal depression].

Melatonin (MEL) hypothesis in seasonal affective disorders (SAD) is supported by: a) historical hint; b) circadian and seasonal MEL periodicity with evidence that the SAD is related to photoperiod; c) relationship between incidence and severity of SAD and latitude; d) the response to bright artificial light (ineffective in depression) which mimics summer time; e) MEL administration can induce some symptoms of the SAD; f) several antidepressant drugs increase MEL plasma levels. Several of these findings are disproved: the light acts independently from the MEL, some antidepressant agents act without modifying MEL levels; a consistent alteration in MEL secretion within SAD has not been convincingly demonstrated. Relationship between incidence and severity of SAD and latitude suggests a new potential implication of MEL in SAD. The daytime melatonin values reflect changes along the scale of a year in sunshine. Accordingly, the about-yearly periodicity, much larger in amplitude than the half-yearly component, yields ratios smaller than unity. By contrast during darkness an about-half-yearly component is more prominent. As the aurora zone is approached, the intensity of magnetic disturbances increases. Thus, the intensity of these two variables shows inverse relationships with latitude and geomagnetic field decreases plasma levels of MEL and inhibits MEL function.

Circadian Rhythm↗