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Urinary 6‐sulfatoxymelatonin profiles in male Djungarian hamsters ( Phodopus sungorus ) responding and not responding to short‐day photoperiods: Possible role of elevated daytime levels
Author(s) -
Niehaus Michael,
Lerchl Alexander
Publication year - 1998
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.1998.tb00555.x
Subject(s) - phodopus , medicine , endocrinology , melatonin , circadian rhythm , photoperiodism , biology , excretion , context (archaeology) , hamster , pineal gland , paleontology
The lack of endocrine and physiological responses of some Djungarian hamsters ( Phodopus sungorus ) to the transition from long to short photoperiods (L:D 16:8 → L:D 8:16) has been known for a long time but is not yet understood. We investigated the role of melatonin synthesis in this context because melatonin, as part of the circadian system, may play a role in non‐responsiveness. In ten responding and ten non‐responding male hamsters, the urinary 24 hr 6‐sulfatoxymelatonin (aMT6s) profiles under L:D 8:16 and L:D 16:8 were measured. Both short day responding and non‐responding hamsters showed diurnal aMT6s excretion rhythms. Whereas responders reacted to the transition L:D 16:8 → L:D 8:16 with a marked elevation of aMT6s excretion, in non‐responders no adjustment of the melatonin rhythm to the change of the photoperiod was seen. Furthermore, under L:D 16:8 the daytime levels of aMT6s were significantly ( p <0.001) lower in responders compared to non‐responders whereas under L: D 8: 16 these levels were higher ( p <0.01). It is speculated that high daytime levels of aMT6s under long‐day photoperiods in non‐responders result in down‐regulation of melatonin receptors of the nucleus suprachiasmaticus, the pacemaker for the pineal gland, leading to a lack of response to the transition to short‐day photoperiods.