title: Relationship between growth hormone in vivo bioactivity, the insulin-like growth factor-I system and bone mineral density in young, physically fit men and women.
abstract: BACKGROUND
  Bone mineral density (BMD) is influenced by growth factors, such as growth hormone (GH) and insulin-like growth factor-I (IGF-I). The in vivo bioassay for GH (bioGH) provides a more physiologically relevant measurement than an in vitro immunoassay, since bioGH is quantified on a biological outcome.
  
  
  OBJECTIVE
  To determine if bioGH and components of the IGF-I system were associated with BMD in age-matched men (M; n=41, 19.1+/-0.2 year, 70+/-3 kg, 163+/-25 cm) and women (W; n=39, 18.6+/-0.3 year, 66+/-3 kg, 141+/-15 cm).
  
  
  METHODS
  Blood was analyzed for growth-related hormones [bioGH, immunoreactive growth hormone (iGH), IGF-I and associated binding proteins], and BMD was measured by pDXA, pQCT, and central DXA (spine, hip). For the bioGH assay, hypophysectomizied female Sprague-Dawley rats were injected with a s.c. bolus of either a GH standard or unknown (each subject's plasma) in four daily injections. The tibia was then examined for epiphyseal growth plate width from which bioGH concentrations were extrapolated.
  
  
  RESULTS
  M had greater (P<0.05) calcaneal BMD when measured by pDXA (M: 1.27+/-0.02; W: 1.14+/-0.02 g/cm2), while pQCT-assessed BMD at the tibia was not different (M: 777+/-16; W: 799+/-16 g/cm2). bioGH was similar between M (5388+/-800 microg/L) and W (4282+/-643 microg/L) and was not correlated with BMD. The only BMD-related biomarkers in women were acid-labile subunit (ALS; r=0.40) and IGFBP-3 (r=0.42) with DXA-measured spine and femoral neck BMD, and ALS (r=0.47) with pQCT-assessed tibial BMD and cortical thickness, respectively.
  
  
  CONCLUSIONS
  Although bioGH was not associated with BMD, IGF-I and associated binding proteins (IGFBP-3 and ALS) emerged as correlates in W only.
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Kansas Street, Building 42, Natick, MA 01760-5007, USA.
authors.forename: B C
authors.initials: BC
authors.lastname: Nindl
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Kansas Street, Building 42, Natick, MA 01760-5007, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Pierce
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Kansas Street, Building 42, Natick, MA 01760-5007, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Durkot
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Kansas Street, Building 42, Natick, MA 01760-5007, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Tuckow
authors.affiliation: Central Biological Laboratory, The Pennsylvania State University, State College, PA 01830, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kennett
authors.affiliation: Clinical Research and Regional Bone Centers, Helen Hayes Hospital, West Haverstraw, NY, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Nieves
authors.affiliation: Clinical Research and Regional Bone Centers, Helen Hayes Hospital, West Haverstraw, NY, USA.
authors.forename: F
authors.initials: F
authors.lastname: Cosman
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Kansas Street, Building 42, Natick, MA 01760-5007, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Alemany
authors.affiliation: Central Biological Laboratory, The Pennsylvania State University, State College, PA 01830, USA.
authors.forename: W C
authors.initials: WC
authors.lastname: Hymer
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D015519:Bone Density / Q000502:physiology*; D005260:Female; D019382:Human Growth Hormone / Q000097:blood / Q000378:metabolism*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I