title: Effects of simulated weightlessness on bone metabolism in rats at different ages.
abstract: OBJECTIVE
  To compare the effects of simulated weightlessness on age-related bone metabolism and on the mechanical parameters of the weight-bearing bones of rats at different ages.
  
  
  METHODS
  Two-month-old and 6-month-old rats (8 in each group) were both subjected to tail suspension test for up to 4 weeks, with 2 groups of rats of corresponding ages (n=8) serving as control. The bone metabolism markers, biomechanical parameters of the femurs, along with the growth and mineral contents of the tibia, were respectively measured and compared with those of the controls.
  
  
  RESULTS
  The bone formation markers, alkaline phosphatase and osteocalcin levels, dropped drastically in both groups of rats undergoing tail suspension test (P<0.01), which also induced significant hypocalcaemia (P<0.01). Bone material loss of the tibia occurred in both groups of rats receiving the test (P<0.01) whose effect on the volume and mass of fresh tibia was age-related (P<0.05), but the degree of mineral loss was not consistent with calcium loss in rats at different ages. Except for elastic deformation (P>0.05), both structural and biomechanical properties altered significantly after tail suspension test (P<0.01), and the changes of maximum deformation and maximum load were related to the age of the rats (P<0.05).
  
  
  CONCLUSIONS
  The result is an age-related difference in the response of bone metabolism to simulated weightlessness.
authors.affiliation: Department of Orthopedics and Traumatology, Nanfang Hospital, First Military Medical University, Guangzhou 510515, China. txj@fimmu.com
authors.forename: Xiong-Jin
authors.initials: XJ
authors.lastname: Tan
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Zheng
authors.forename: Yong-Jian
authors.initials: YJ
authors.lastname: Sun
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000378:metabolism* / Q000502:physiology; D008297:Male; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D014893:Weightlessness / Q000009:adverse effects*; D018474:Weightlessness Simulation