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Entrainment of the circadian rhythm in the rat pineal N‐acetyltransferase activity by melatonin is photoperiod dependent
Author(s) -
Humlová Martina,
Lllnerová Helena
Publication year - 1992
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1992.tb00070.x
Subject(s) - melatonin , zeitgeber , photoperiodism , circadian rhythm , endocrinology , medicine , evening , entrainment (biomusicology) , biology , period (music) , light effects on circadian rhythm , pineal gland , rhythm , circadian clock , physics , astronomy , acoustics
Entraining effect of melatonin on the circadian rhythm in rat pineal N‐acetyltransferase (NAT) activity was studied under various photoperiods. Melatonin administration prior to dark onset for 5 successive days phase‐advanced the evening NAT rise under the light:dark (LD) cycle of either LD 10:14 or LD 8:16, but not under LD 12:12. It is assumed that under the latter regime, the end of a light period exhibited a phase‐delaying effect on the NAT rise. The light exposure appeared to be a stronger Zeitgeber than melatonin itself. Data show that melatonin applied in the late light period advances the evening NAT rise under a short photoperiod only; under a longer photoperiod, the phase‐advancing effect of melatonin may conflict with a phase‐delaying effect of the end of a light period, and the effect of light exposure overrides that of melatonin.