title: Nocturnal oxytocin secretion is lower in amenorrheic athletes than nonathletes and associated with bone microarchitecture and finite element analysis parameters.
abstract: OBJECTIVE
  Preclinical data indicate that oxytocin, a hormone produced in the hypothalamus and secreted into the peripheral circulation, is anabolic to bone. Oxytocin knockout mice have severe osteoporosis, and administration of oxytocin improves bone microarchitecture in these mice. Data suggest that exercise may modify oxytocin secretion, but this has not been studied in athletes in relation to bone. We therefore investigated oxytocin secretion and its association with bone microarchitecture and strength in young female athletes.
  
  
  METHODS
  Cross-sectional study of 45 females, 14-21 years (15 amenorrheic athletes (AA), 15 eumenorrheic athletes (EA), and 15 nonathletes (NA)), of comparable bone age and BMI.
  
  
  METHODS
  We used high-resolution peripheral quantitative CT to assess bone microarchitecture and finite element analysis to estimate bone strength at the weight-bearing distal tibia and non-weight-bearing ultradistal radius. Serum samples were obtained every 60  min, 2300-0700  h, and pooled for an integrated measure of nocturnal oxytocin secretion. Midnight and 0700  h samples were used to assess diurnal variation of oxytocin.
  
  
  RESULTS
  Nocturnal oxytocin levels were lower in AA and EA than in NA. After controlling for estradiol, the difference in nocturnal oxytocin between AA and NA remained significant. Midnight and 0700  h oxytocin levels did not differ between groups. At the tibia and radius, AA had impaired microarchitecture compared with NA. In AA, nocturnal oxytocin correlated strongly with trabecular and cortical microarchitecture, particularly at the non-weight-bearing radius. In regression models that include known predictors of microarchitecture in AA, oxytocin accounted for a substantial portion of the variability in microarchitectural and strength parameters.
  
  
  CONCLUSIONS
  Nocturnal oxytocin secretion is low in AA compared with NA and associated with site-dependent microarchitectural parameters. Oxytocin may contribute to hypoestrogenemic bone loss in AA.
authors.affiliation: Neuroendocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA. ealawson@partners.org
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Lawson
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Ackerman
authors.forename: Nara Mendes
authors.initials: NM
authors.lastname: Estella
authors.forename: Gabriela
authors.initials: G
authors.lastname: Guereca
authors.forename: Lisa
authors.initials: L
authors.lastname: Pierce
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Sluss
authors.forename: Mary L
authors.initials: ML
authors.lastname: Bouxsein
authors.forename: Anne
authors.initials: A
authors.lastname: Klibanski
authors.forename: Madhusmita
authors.initials: M
authors.lastname: Misra
mesh_terms: D000293:Adolescent; D000328:Adult; D000568:Amenorrhea / Q000097:blood* / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology; D056352:Athletes; D015992:Body Mass Index; D001862:Bone Resorption / Q000209:etiology; D001842:Bone and Bones / Q000737:chemistry / Q000473:pathology*; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D015444:Exercise; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism*; D055595:Mechanical Phenomena; D010121:Oxytocin / Q000097:blood / Q000172:deficiency / Q000378:metabolism*; D011884:Radius / Q000737:chemistry / Q000473:pathology; D013977:Tibia / Q000737:chemistry / Q000473:pathology; D016474:Weight-Bearing; D055815:Young Adult
chemical_list: D010121:Oxytocin