title: Pineal melatonin is a circadian time-giver for leptin rhythm in Syrian hamsters.
abstract: Nocturnal secretion of melatonin from the pineal gland may affect central and peripheral timing, in addition to its well-known involvement in the control of seasonal physiology. The Syrian hamster is a photoperiodic species, which displays gonadal atrophy and increased adiposity when adapted to short (winter-like) photoperiods. Here we investigated whether pineal melatonin secreted at night can impact daily rhythmicity of metabolic hormones and glucose in that seasonal species. For that purpose, daily variations of plasma leptin, cortisol, insulin and glucose were analyzed in pinealectomized hamsters, as compared to sham-operated controls kept under very long (16 h light/08 h dark) or short photoperiods (08 h light/16 h dark). Daily rhythms of leptin under both long and short photoperiods were blunted by pinealectomy. Furthermore, the phase of cortisol rhythm under a short photoperiod was advanced by 5.6 h after pinealectomy. Neither plasma insulin, nor blood glucose displays robust daily rhythmicity, even in sham-operated hamsters. Pinealectomy, however, totally reversed the decreased levels of insulin under short days and the photoperiodic variations in mean levels of blood glucose (i.e., reduction and increase in long and short days, respectively). Together, these findings in Syrian hamsters show that circulating melatonin at night drives the daily rhythmicity of plasma leptin, participates in the phase control of cortisol rhythm and modulates glucose homeostasis according to photoperiod-dependent metabolic state.
authors.affiliation: Laboratory of Biology and Health, Faculty of Science, Abdelmalek Essaâdi University Tetouan, Morocco ; Regulation of Circadian Clocks Team, Institute for Cellular and Integrative Neurosciences, UPR3212, Centre National de la Recherche Scientifique and University of Strasbourg Strasbourg, France.
authors.forename: Ibtissam
authors.initials: I
authors.lastname: Chakir
authors.affiliation: Regulation of Circadian Clocks Team, Institute for Cellular and Integrative Neurosciences, UPR3212, Centre National de la Recherche Scientifique and University of Strasbourg Strasbourg, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Dumont
authors.affiliation: Regulation of Circadian Clocks Team, Institute for Cellular and Integrative Neurosciences, UPR3212, Centre National de la Recherche Scientifique and University of Strasbourg Strasbourg, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Pévet
authors.affiliation: Laboratory of Biology and Health, Faculty of Science, Abdelmalek Essaâdi University Tetouan, Morocco.
authors.forename: Ali
authors.initials: A
authors.lastname: Ouarour
authors.affiliation: Regulation of Circadian Clocks Team, Institute for Cellular and Integrative Neurosciences, UPR3212, Centre National de la Recherche Scientifique and University of Strasbourg Strasbourg, France.
authors.forename: Etienne
authors.initials: E
authors.lastname: Challet
authors.affiliation: Regulation of Circadian Clocks Team, Institute for Cellular and Integrative Neurosciences, UPR3212, Centre National de la Recherche Scientifique and University of Strasbourg Strasbourg, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Vuillez
keywords: cortisol rhythm; golden hamster; photoperiod; pinealectomy; plasma glucose