title: Urinary 6-sulfatoxymelatonin profiles in male Djungarian hamsters (Phodopus sungorus) responding and not responding to short-day photoperiods: possible role of elevated daytime levels.
abstract: 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.
authors.affiliation: Institute of Reproductive Medicine of the University, Münster, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Niehaus
authors.forename: A
authors.initials: A
authors.lastname: Lerchl
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D015536:Down-Regulation; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D017111:Phodopus; D017440:Photoperiod; D011863:Radioimmunoassay; D011956:Receptors, Cell Surface / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D044094:Receptors, Melatonin
chemical_list: D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; C054513:6-sulfatoxymelatonin; D008550:Melatonin