title: Circadian variation in endothelial function is attenuated in postmenopausal women.
abstract: OBJECTIVE
  The present study was undertaken to investigate the possible existence of an endogenously generated circadian rhythm in endothelial function in women and whether this rhythm is altered after the menopause.
  
  
  METHODS
  Healthy non smoking women (11 pre-menopausal and 13 postmenopausal women) were studied during a 22 h period under constant routine conditions; endothelium-dependent (flow-mediated dilation (%FMD)) and -independent (glyceryl-trintrate (GTN)-mediated) function was assessed every 2 and 4 h, respectively, by high-resolution ultrasound of the brachial artery.
  
  
  RESULTS
  %FMD and %GTN was significantly higher in pre-menopausal women (9.9+/-1.0%FMD (mean+/-S.E.M.); 18.2+/-1.8%GTN; P<0.01) compared with postmenopausal women (6.5+/-0.5%FMD; 11.5+/-1.6%GTN). A significant day-night variation in %FMD was observed pre-menopausal women (day 9.2+/-0.8%; night 10.4+/-1%; P<0.05) with an attenuated rhythm in postmenopausal women (day 6.8+/-0.6%; night 6.0+/-0.4%).
  
  
  CONCLUSIONS
  The findings show a circadian rhythm in %FMD in pre-menopausal women, which disappears after the menopause. The reduction in %FMD and an absence of a day-night variation in %FMD in postmenopausal women may have important implications for the incidence of coronary heart disease in women after the menopause.
authors.affiliation: Neuroendocrinology Group, School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK. j.walters@surrey.ac.uk
authors.forename: Janie F
authors.initials: JF
authors.lastname: Walters
authors.forename: Shelagh M
authors.initials: SM
authors.lastname: Hampton
authors.forename: John E
authors.initials: JE
authors.lastname: Deanfield
authors.forename: Ann E
authors.initials: AE
authors.lastname: Donald
authors.forename: Debra J
authors.initials: DJ
authors.lastname: Skene
authors.forename: Gordon A A
authors.initials: GA
authors.lastname: Ferns
mesh_terms: D000328:Adult; D001132:Arm / Q000098:blood supply*; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D002940:Circadian Rhythm; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008875:Middle Aged; D017698:Postmenopause; D014463:Ultrasonography; D014664:Vasodilation / Q000502:physiology