Interactions between endocrine and circadian systems

  1. Henrik Oster1,2
  1. 1Circadian Rhythms Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
    2Chronophysiology Group, Medical Department I, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
    3School of Medicine, University of Queensland, Brisbane, Queensland, Australia
  1. Correspondence should be addressed to H Oster; Email: henrik.oster{at}
  1. Figure 1

    The molecular mammalian circadian clockwork. The transcription factors Clock/Npas2 and Bmal1 activate E-box-controlled genes including PER1–3 and CRY1/2 during the day. PER and CRY proteins inhibit CLOCK/BMAL1 activity during the night. Auxiliary loops stabilize this 24-h rhythm of transcriptional activation by modulating gene expression of Bmal1 and Per. For details see text.

  2. Figure 2

    Interaction of central and peripheral clocks in the regulation of GC secretion. The SCN innervates the PVN from where rhythmic CRH release triggers secretion of ACTH from the pituitary (PIT). At the same time autonomic innervation (ANS) of the adrenal resets adrenocortical clocks regulating sensitivity of the steroidogenic machinery to ACTH. Synchrony between HPA axis activity and adrenal ACTH gating results in high amplitude and robust circadian GC rhythms. GC rhythms are phase-shifted between nocturnal and diurnal species indicating differential interpretation of SCN signals at downstream targets.

  3. Figure 3

    Melatonin release from the pineal is driven by the SCN pacemaker. The SCN innervates the PVN from where autonomous fibres descend into the spinal cord and out via the superior cervical ganglia (SCG) to reach the pineal gland (PIN). Clock genes are expressed in the pineal, but a functional contribution of a potential pineal clock to melatonin production has not been demonstrated. Unlike GCs, melatonin secretion is always confined to the dark phase, regardless of the activity profile of the animal.

  4. Figure 4

    Endocrine feedback to the circadian clock. Various hormones can directly or indirectly feedback on central and peripheral clock function. In the brain endocrine targets with connections to the SCN include the orexinergic neurons of the lateral hypothalamus (LH), the arcuate nucleus (ARC), and the raphe nuclei of the brainstem. Other endocrine effects may be mediated via peripheral tissues and clocks such as the liver and muscle. For details see text.

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