bims-ciryme Biomed News
on Circadian rhythms and metabolism
Issue of 2019‒08‒18
two papers selected by
Gabriela Da Silva Xavier
University of Birmingham

  1. Nat Rev Endocrinol. 2019 Aug 12.
      Circadian rhythmicity is an approximately 24-h cell-autonomous period driven by transcription-translation feedback loops of specific genes, which are referred to as 'circadian clock genes'. In mammals, the central circadian pacemaker, which is located in the hypothalamic suprachiasmatic nucleus, controls peripheral circadian clocks. The circadian system regulates virtually all physiological processes, which are further modulated by changes in the external environment, such as light exposure and the timing of food intake. Chronic circadian disruption caused by shift work, travel across time zones or irregular sleep-wake cycles has long-term consequences for our health and is an important lifestyle factor that contributes to the risk of obesity, type 2 diabetes mellitus and cancer. Although the hypothalamic-pituitary-thyroid axis is under the control of the circadian clock via the suprachiasmatic nucleus pacemaker, daily TSH secretion profiles are disrupted in some patients with hypothyroidism and hyperthyroidism. Disruption of circadian rhythms has been recognized as a perturbation of the endocrine system and of cell cycle progression. Expression profiles of circadian clock genes are abnormal in well-differentiated thyroid cancer but not in the benign nodules or a healthy thyroid. Therefore, the characterization of the thyroid clock machinery might improve the preoperative diagnosis of thyroid cancer.
  2. J Clin Endocrinol Metab. 2019 Aug 15. pii: jc.2019-00803. [Epub ahead of print]
      CONTEXT: Studies suggest that female reproductive hormones are under circadian regulation, although methodologic differences have led to inconsistent findings.OBJECTIVE: To determine whether circulating levels of reproductive hormones exhibit circadian rhythms.
    DESIGN: Blood samples were collected across ∼90 consecutive hours, including 2 baseline days under a standard sleep-wake schedule, and ∼50 hours of extended wake under constant routine (CR) conditions.
    SETTING: Intensive Physiological Monitoring Unit, Brigham and Women's Hospital.
    PARTICIPANTS: Seventeen healthy pre-menopausal women (22.8 ± 2.6 years; 9 follicular; 8 luteal).
    MAIN OUTCOMES MEASURES: Plasma estradiol (E2), progesterone (P4), luteinizing hormone (LH), follicle stimulating hormone (FSH), sex-hormone binding globulin (SHBG), melatonin and core body temperature.
    RESULTS: All hormones exhibited significant 24-h rhythms under both standard sleep-wake and CR conditions during the follicular phase (p<0.05). In contrast, only FSH and SHBG were significantly rhythmic during the luteal phase. Rhythm acrophases and amplitudes were similar between standard sleep-wake and CR conditions. The acrophase occurred in the morning for P4, in the afternoon for FSH, LH and SHBG and during the night for E2.
    CONCLUSIONS: Our results confirm previous reports of ∼24-h rhythms in many female reproductive hormones in humans under ambulatory conditions but demonstrate that these hormones are under endogenous circadian regulation, defined as persisting in the absence of external time cues. These results may have important implications for the effects of circadian disruption on reproductive function.