Endogenous Circadian Regulation of Female Reproductive Hormones

Context: Studies suggest that female reproductive hormones are under circadian regulation, although methodological 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 premenopausal women (22.8 ± 2.6 years; nine follicular; eight luteal). Interventions: Fifty-hour CR. Main Outcome Measures: Plasma estradiol (E2), progesterone (P4), LH, FSH, SHBG, melatonin, and core body temperature. Results: All hormones exhibited significant 24-hour 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-hour 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. Copyright © 2019 Endocrine Society

Constraint is associated with earlier circadian phase and morningness: Confirmation of relationships between personality and circadian phase using a constant routine protocol

Associations amongst personality, diurnal preference, and circadian phase were investigated using a constant routine laboratory protocol. One hundred and sixty-eight healthy participants aged 18�30 years (Women n = 68) completed either a 30- or 50-hour constant routine under dim-light conditions (< 3 lx), during which circadian phase was measured from core body temperature and melatonin. Prior to laboratory admission, self-report measures of personality and diurnal preference were also obtained. The personality trait of Constraint correlated positively with morning diurnal preference and earlier circadian phase, with circadian phase partially mediating the relationship between Constraint and diurnal preference. No other personality variables correlated with circadian phase. Sex was an important covariate in several of the relationships investigated due to lower levels of Constraint and later CBT phase amongst men and was thus controlled for in all relevant analyses. Findings from this highly controlled study are consistent with previous field research in suggesting that earlier circadian phase is associated with the personality trait of Constraint. © 201

Individual differences in physiologic measures are stable across repeated exposures to total sleep deprivation

10.14814/phy2.12129Physiological Reports29e1212