title: Diurnal cortisol changes in newborn infants suggesting entrainment of peripheral circadian clock in utero and at birth.
abstract: BACKGROUND
  In the rodent and human fetus, a diurnal cortisol rhythm is observed that is entrained in antiphase to the maternal rhythm. However, after birth, the adrenal circadian rhythm becomes unsynchronized with the clock time, and an adult-type, 24-h rhythm is observed only after a few months. Little is known about when and how the fetal adrenal circadian rhythm is synchronized with the day-night cycle.
  
  
  METHODS
  To investigate the function of adrenal circadian clock in the newborn infant, eight serial saliva samples were collected every 3 h over 24 h (starting at 0900 h) in 27 newborn infants.
  
  
  RESULTS
  Cortisol levels were higher during the period 1500 to earlier than 2100 h than during 0900 to earlier than 1500 h and 0300 to earlier than 0900 h (both P < 0.05). Salivary cortisol levels collected during 0 to <6, 6 to <12, and 12 to <18 hours after the clock time at birth (birth time) were higher than those collected during 18 to <24 hours after the birth time (P < 0.005, 0.05, and 0.05, respectively). The acrophase of salivary cortisol was linearly correlated with the birth time within the first 5 d of life (P < 0.005) but not thereafter.
  
  
  CONCLUSIONS
  In the newborn infant, diurnal increase in cortisol was observed in the late afternoon and in correspondence with the birth time. The adrenal circadian rhythm acquired in utero may be reentrained by endocrinological events at birth. Such complex regulation of the adrenal circadian clock may inhibit a swift synchronization of the circadian clock to the day-night rhythm.
authors.affiliation: Centre for Developmental and Cognitive Neuroscience, Department of Paediatrics and Child Health, Kurume University School of Medicine, 67 Asahimachi, Kurume, Fukuoka 830-0011 Japan. o.iwata@ucl.ac.uk
authors.forename: Osuke
authors.initials: O
authors.lastname: Iwata
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Okamura
authors.forename: Hiroki
authors.initials: H
authors.lastname: Saitsu
authors.forename: Mamoru
authors.initials: M
authors.lastname: Saikusa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kanda
authors.forename: Nobuoki
authors.initials: N
authors.lastname: Eshima
authors.forename: Sachiko
authors.initials: S
authors.lastname: Iwata
authors.forename: Yasuki
authors.initials: Y
authors.lastname: Maeno
authors.forename: Toyojiro
authors.initials: T
authors.lastname: Matsuishi
mesh_terms: D000328:Adult; D057906:Circadian Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007231:Infant, Newborn / Q000378:metabolism* / Q000502:physiology; D008297:Male; D036801:Parturition / Q000378:metabolism* / Q000502:physiology; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000378:metabolism* / Q000503:physiopathology; D012463:Saliva / Q000378:metabolism; D013997:Time Factors
chemical_list: D006854:Hydrocortisone