Keeping circadian time with hormones

Sep 3, 2015Diabetes, obesity & metabolism

How hormones help keep the body’s internal clock on time

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Circadian desynchronization may increase metabolic risks, contributing to diabetes and obesity.

Daily variations in metabolism and behavior are regulated by a network of circadian clocks, including a master clock in the hypothalamus and secondary clocks in other organs.
Light cues synchronize the master clock, which sends signals to other body clocks through neuronal and hormonal pathways.
Feeding at atypical times can reset the phase of peripheral clocks, indicating the influence of meal timing on circadian rhythms.
Hormonal signals from adrenal glucocorticoids, melatonin, and leptin function as internal time-givers that help synchronize the body's clocks.
Circadian deregulation may arise from factors like shift work or chronic jet lag, negatively affecting metabolic regulation.

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Daily variations of metabolism, physiology and behaviour are controlled by a network of coupled circadian clocks, comprising a master clock in the suprachiasmatic nuclei of the hypothalamus and a multitude of secondary clocks in the brain and peripheral organs. Light cues synchronize the master clock that conveys temporal cues to other body clocks via neuronal and hormonal signals. Feeding at unusual times can reset the phase of most peripheral clocks. While the neuroendocrine aspect of circadian regulation has been underappreciated, this review aims at showing that the role of hormonal rhythms as internal time-givers is the rule rather than the exception. Adrenal glucocorticoids, pineal melatonin and adipocyte-derived leptin participate in internal synchronization (coupling) within the multi-oscillatory network. Furthermore, pancreatic insulin is involved in food synchronization of peripheral clocks, while stomach ghrelin provides temporal signals modulating behavioural anticipation of mealtime. Circadian desynchronization induced by shift work or chronic jet lag has harmful effects on metabolic regulation, thus favouring diabetes and obesity. Circadian deregulation of hormonal rhythms may participate in internal desynchronization and associated increase in metabolic risks. Conversely, adequate timing of endocrine therapies can promote phase-adjustment of the master clock (e.g. via melatonin agonists) and peripheral clocks (e.g. via glucocorticoid agonists).

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Keeping circadian time with hormones

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