title: Recovery of the rat skeleton from the adverse effects of simulated weightlessness.
abstract: A rat model that involves total mechanical unloading of the hind limbs has been used to simulate some aspects of weightlessness. In a previous study, the presence of marked skeletal abnormalities in the proximal tibial and humeral metaphyses of unloaded rats was detected. In the current study, the rats were removed from the model after a 2-week suspension period and allowed to recover for 2 weeks in individual metabolic cages before sacrifice. Tetracycline derivatives were administered on three separate occasions to evaluate radial and longitudinal bone growth. Periosteal bone formation in the tibial diaphysis of suspended animals was significantly depressed during the suspension period but approached control levels during the recovery period. Periosteal bone formation in the humeral diaphysis was not affected by simulated weightlessness. In the proximal tibial and humeral metaphyses, longitudinal bone growth, the amount of mineralized tissue, and the fat content of the bone marrow, all of which were previously determined to be abnormal after 2 weeks of simulated weightlessness, returned to control levels during the recovery period. The previously observed decline in the osteoblast population and increased numbers of osteoclasts adjacent to the growth plate in suspended animals also proved to be reversible at both skeletal sites. This study demonstrates that the skeleton of growing rats is capable of a rapid recovery from the adverse effects of simulated weightlessness.
mesh_terms: D000818:Animals; D001835:Body Weight; D001846:Bone Development; D001842:Bone and Bones / Q000473:pathology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014893:Weightlessness / Q000009:adverse effects*