Keeping circadian time with hormones

Area of Science:

• Chronobiology
• Endocrinology
• Metabolic Regulation

Background:

• Daily physiological and behavioral rhythms are governed by coupled circadian clocks.
• The suprachiasmatic nuclei (SCN) master clock synchronizes peripheral clocks via neuronal and hormonal signals.
• Light is a primary synchronizer, but feeding times also reset peripheral clocks.

Purpose of the Study:

• To highlight the underappreciated role of neuroendocrine rhythms in circadian regulation.
• To demonstrate that hormonal rhythms act as crucial internal time-givers.
• To review the involvement of specific hormones in circadian synchronization and metabolic health.

Main Methods:

• Review of existing literature on circadian clocks and hormonal signaling.
• Analysis of the roles of glucocorticoids, melatonin, leptin, insulin, and ghrelin in circadian timing.
• Examination of the consequences of circadian desynchronization on metabolic regulation.

Main Results:

• Hormonal rhythms, including adrenal glucocorticoids, pineal melatonin, and adipocyte leptin, are essential for synchronizing the multi-oscillatory circadian network.
• Pancreatic insulin synchronizes peripheral clocks with feeding schedules, while ghrelin signals anticipate mealtime.
• Circadian desynchronization, often from shift work or jet lag, disrupts metabolic regulation, increasing risks for diabetes and obesity.

Conclusions:

• Hormonal rhythms are fundamental to internal time-giving and circadian network synchronization.
• Dysregulation of these hormonal rhythms contributes to internal desynchronization and elevated metabolic risks.
• Strategic timing of endocrine therapies can be used to adjust master and peripheral circadian clocks, potentially improving metabolic health.