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Human circadian rhythm in serum melatonin in short winter days and in simulated artificial long days
M Buresová1, M Dvoráková, P Zvolský
1Institute of Physiology, Czechoslovak Academy of Sciences, Prague.
Neuroscience Letters
|March 2, 1992
Abstract:
Serum melatonin rhythm was studied in 6 human subjects experiencing short winter days resembling light/dark (LD) 8:16 h and in 6 subjects exposed at the same time to a long, LD 16:8 h skeleton photoperiod, with 3 h of bright light in the evening and again in the morning; 4 out of the 6 subjects entrained to the simulated summer photoperiod within 3 days. In the synchronized subjects, the nocturnal melatonin signal was 3 h shorter than in those experiencing just winter days. The data indicate that humans are able to respond to environmental day length by forming a proper endogenous photoperiodic signal.