title: Changes in the diurnal rhythms during a 45-day head-down bed rest.
abstract: In spaceflight human circadian rhythms and sleep patterns are likely subject to change, which consequently disturbs human physiology, cognitive abilities and performance efficiency. However, the influence of microgravity on sleep and circadian clock as well as the underlying mechanisms remain largely unknown. Placing volunteers in a prone position, whereby their heads rest at an angle of -6° below horizontal, mimics the microgravity environment in orbital flight. Such positioning is termed head-down bed rest (HDBR). In this work, we analysed the influence of a 45-day HDBR on physiological diurnal rhythms. We examined urinary electrolyte and hormone excretion, and the results show a dramatic elevation of cortisol levels during HDBR and recovery. Increased diuresis, melatonin and testosterone were observed at certain periods during HDBR. In addition, we investigated the changes in urination and defecation frequencies and found that the rhythmicity of urinary frequency during lights-off during and after HDBR was higher than control. The grouped defecation frequency data exhibits rhythmicity before and during HDBR but not after HDBR. Together, these data demonstrate that HDBR can alter a number of physiological processes associated with diurnal rhythms.
authors.affiliation: Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Xiaodi
authors.initials: X
authors.lastname: Liang
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Wan
authors.forename: Xinyang
authors.initials: X
authors.lastname: Yu
authors.forename: Yiming
authors.initials: Y
authors.lastname: Guo
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Chen
authors.forename: Cheng
authors.initials: C
authors.lastname: Tan
authors.forename: Tianle
authors.initials: T
authors.lastname: Huang
authors.forename: Hanjie
authors.initials: H
authors.lastname: Shen
authors.forename: Xianyun
authors.initials: X
authors.lastname: Chen
authors.forename: Hongying
authors.initials: H
authors.lastname: Li
authors.forename: Ke
authors.initials: K
authors.lastname: Lv
authors.forename: Fei
authors.initials: F
authors.lastname: Sun
authors.forename: Shanguang
authors.initials: S
authors.lastname: Chen
authors.forename: Jinhu
authors.initials: J
authors.lastname: Guo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001510:Bed Rest; D002940:Circadian Rhythm / Q000502:physiology*; D003672:Defecation / Q000502:physiology; D004573:Electrolytes / Q000652:urine; D018475:Head-Down Tilt / Q000502:physiology*; D006728:Hormones / Q000652:urine; D006801:Humans; D008297:Male; D010507:Periodicity; D011188:Potassium / Q000652:urine; D012964:Sodium / Q000652:urine; D013997:Time Factors; D014554:Urination; D014556:Urine / Q000502:physiology; D018474:Weightlessness Simulation; D055815:Young Adult
chemical_list: D004573:Electrolytes; D006728:Hormones; D012964:Sodium; D011188:Potassium