title: Cortical bone responses to 2G hypergravity in growing rats.
abstract: BACKGROUND
  Rat cortical bone adaptation to chronic hypergravity (2G) was studied using young growing male Wistar rats (60 d).
  
  
  METHODS
  Animals (10 rats) were subjected to chronic hypergravity (14 d) in order to understand the plastic nature of bone under a constant hypergravity stress using a special rodent habitat that was attached to a 12-ft. radius centrifuge. Also, an equal number of stationary controls were housed in a rodent vivarium containing identical cages that were used for centrifugation. After 14 d of centrifugation, femur bones were excised and prepared for morphological and biochemical measurements.
  
  
  RESULTS
  Results showed that 2G had significantly shortened the femurs (3%) and reduced the cortical bone area (13%). In particular, hypergravity induced significant reductions in the thicknesses of cortical bone at the anterior (13%) and medial regions (15%) of the mid-diaphysis. However, femoral bone density, collagen and calcium concentrations were unaltered. The content of mature, stable bone collagen cross-links hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), were significantly greater in bones from centrifuged animals.
  
  
  CONCLUSIONS
  Our findings suggest that short term exposure to 2G does not enhance bone formation or induce changes in cortical bone composition, or alter specific gravity. These data also suggest that bone maturation as reflected by collagen cross-linking is upregulated. However, it is undetermined at this time whether the enhanced content of mature bone collagen in the centrifuged rats is a result of either an increased rate of cross-linking or reduction in the degradation of "older collagen."
authors.affiliation: Department of Biology and Biochemistry, University of Houston, TX 77204-5513, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Martinez
authors.forename: M W
authors.initials: MW
authors.lastname: Orth
authors.forename: K E
authors.initials: KE
authors.lastname: Carr
authors.forename: R
authors.initials: R
authors.lastname: Vanderby
authors.forename: M
authors.initials: M
authors.lastname: Vasques
authors.forename: R E
authors.initials: RE
authors.lastname: Grindeland
authors.forename: A C
authors.initials: AC
authors.lastname: Vailas
mesh_terms: D000222:Adaptation, Physiological; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001835:Body Weight; D015519:Bone Density; D001846:Bone Development / Q000502:physiology*; D002118:Calcium / Q000032:analysis; D002498:Centrifugation / Q000009:adverse effects*; D003094:Collagen / Q000032:analysis; D005269:Femur / Q000737:chemistry / Q000502:physiology*; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D051381:Rats / Q000254:growth & development*; D017208:Rats, Wistar; D013046:Specific Gravity
chemical_list: D000596:Amino Acids; C015484:pyridinoline; C036020:deoxypyridinoline; D003094:Collagen; D002118:Calcium