title: Parathyroid hormone induces formation of new cancellous bone with substantial mechanical strength at a site where it had disappeared in old rats.
abstract: OBJECTIVE
  The present study addresses the question--can PTH induce formation of trabeculae in areas where cancellous bone has disappeared? Two-year-old male rats were chosen, because in this aged animal model the distal femurs have almost no cancellous bone, and the marrow cavity has reached a substantial dimension.
  
  
  METHODS
  The rats were injected for 56 days with either PTH(1-34), 15 nmol/kg/day (62.5 microg/kg/day), or vehicle.
  
  
  METHODS
  Transverse specimens, 2-mm high, were cut from the distal femoral metaphysis. Marrow cavity diameters and cancellous bone trabeculae were analysed by a micro-computerized tomography scanner. The cancellous bone within the cortical and endocortical rim of each specimen was submitted to a biomechanical compression test. Furthermore, the cancellous bone was studied by dynamic tetracycline labelling and histomorphometry.
  
  
  RESULTS
  In the vehicle-injected group the trabecular bone volume was 0% (0-1.4), median (range). All PTH-injected rats had trabeculae in the distal metaphysis and the trabecular bone volume (6.7% (2.3-12.0)) was markedly increased (P<0.003). The median trabecular thickness was increased (P<0.003) in the PTH-injected rats (118 microm (104-125)) compared with the vehicle group (0 microm (0-71)). The compressive stress was increased (P<0.003) in the PTH-injected group (0.7 MPa (0.1-2.1)) compared with the vehicle-injected group (0 MPa (0-0.4)). The histomorphometry revealed that only 3 animals of the 10 in the vehicle-injected group had trabeculae in the distal femoral metaphysis. All PTH-injected animals (12 of 12) had continuous trabecular bone network in the marrow cavity.
  
  
  CONCLUSIONS
  Intermittent PTH treatment induced marked formation of new cancellous bone trabeculae with substantial mechanical strength, at a site where it had disappeared in old rats.
authors.affiliation: Department of Connective Tissue Biology, Institute of Anatomy, Aarhus C, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Oxlund
authors.forename: Michel
authors.initials: M
authors.lastname: Dalstra
authors.forename: Charlotte
authors.initials: C
authors.lastname: Ejersted
authors.forename: Troels T
authors.initials: TT
authors.lastname: Andreassen
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D001846:Bone Development / Q000187:drug effects* / Q000502:physiology; D001853:Bone Marrow / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development; D019245:Compressive Strength; D005269:Femur / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development; D008297:Male; D010281:Parathyroid Hormone / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D014057:Tomography, X-Ray Computed
chemical_list: D010281:Parathyroid Hormone