title: Diurnal rhythm of free estradiol during the menstrual cycle.
abstract: OBJECTIVE
  To investigate the diurnal rhythm of estrogens in normally cyclic women during reproductive life.
  
  
  METHODS
  Multiple saliva sampling in normally cyclic healthy women during reproductive life at different phases of their menstrual cycles was carried out.
  
  
  METHODS
  Salivary estradiol was measured by radioimmunoassay in samples collected every 2 h for 24 h from 15 normally cyclic healthy women during reproductive life during the menstrual phase, the late follicular/peri-ovulation phase, the early to mid luteal phase and the late luteal phase, respectively, of their menstrual cycles. The levels of salivary estradiol were analyzed by means of periodic regression.
  
  
  RESULTS
  A daily biological rhythm of free estradiol was found after quantification with a nonlinear periodic regression model. The observed diurnal free estradiol rhythm consists of two major components: an asymmetrically peaked diurnal cycle and ultradian harmonics in the range of 6 to 12 h. The diurnal and ultradian rhythms were remarkably consistent throughout the menstrual cycle in terms of mesor (24 h mean level), peak width and amplitude. There was a tendency for the 24-h rhythm acrophases to converge in the early morning, while the acrophase of the menstrual phase occurred significantly later than in the late follicular/peri-ovulation phase.
  
  
  CONCLUSIONS
  The diurnal rhythm of estradiol has a similar complex temporal organization for different menstrual phases. The menstrual cycle mainly modulates the acrophase of the diurnal rhythm.
authors.affiliation: Department of Neurobiology, School of Life Science, University of Science and Technology of China, Hefei 230032, Anhui, People's Republic of China.
authors.forename: Ai-Min
authors.initials: AM
authors.lastname: Bao
authors.forename: Rong-Yu
authors.initials: RY
authors.lastname: Liu
authors.forename: Eus J W
authors.initials: EJ
authors.lastname: van Someren
authors.forename: Michel A
authors.initials: MA
authors.lastname: Hofman
authors.forename: Yun-Xia
authors.initials: YX
authors.lastname: Cao
authors.forename: Jiang-Ning
authors.initials: JN
authors.lastname: Zhou
mesh_terms: D000204:Activity Cycles; D000328:Adult; D002940:Circadian Rhythm; D004958:Estradiol / Q000378:metabolism*; D005260:Female; D006801:Humans; D008597:Menstrual Cycle / Q000378:metabolism*; D008954:Models, Biological; D012463:Saliva / Q000378:metabolism*
chemical_list: D004958:Estradiol