title: Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones.
abstract: Previous experiments have shown that skeletal unloading resulting from exposure to microgravity induces osteopenia in rats. In maturing rats, this is primarily a function of reduced formation, rather than increased resorption. Insulin-like growth factor-I (IGF-I) stimulates bone formation by increasing collagen synthesis by osteoblasts. The ability of IGF-I to prevent osteopenia otherwise caused by spaceflight was investigated in 12 rats flown for 10 days aboard the Space Shuttle, STS-77. The effect IGF-I had on cortical bone metabolism was generally anabolic. For example, humerus periosteal bone formation increased a significant 37.6% for the spaceflight animals treated with IGF-I, whereas the ground controls increased 24.7%. This increase in humeral bone formation at the periosteum is a result of an increased percent mineralizing perimeter (%Min.Pm), rather than mineral apposition rate (MAR), for both spaceflight and ground control rats. However, IGF-I did inhibit humerus endocortical bone formation in both the spaceflight and ground control rats (38.1% and 39.2%, respectively) by limiting MAR. This effect was verified in a separate ground-based study. Similar histomorphometric results for spaceflight and ground control rats suggest that IGF-I effects occur during normal weight bearing and during spaceflight. Microhardness measurements of the newly formed bone indicate that the quality of the bone formed during IGF-I treatment or spaceflight was not adversely altered. Spaceflight did not consistently change the structural (force-deflection) properties of the femur or humerus when tested in three-point bending. IGF-I significantly increased femoral maximum and fracture strength.
authors.affiliation: BioServe Space Technologies, Department of Aerospace Engineering Sciences, University of Colorado, Boulder 80309-0429, USA. Ted.Bateman@Colorado.edu
authors.forename: T A
authors.initials: TA
authors.lastname: Bateman
authors.forename: R J
authors.initials: RJ
authors.lastname: Zimmerman
authors.forename: R A
authors.initials: RA
authors.lastname: Ayers
authors.forename: V L
authors.initials: VL
authors.lastname: Ferguson
authors.forename: S K
authors.initials: SK
authors.lastname: Chapes
authors.forename: S J
authors.initials: SJ
authors.lastname: Simske
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D015519:Bone Density / Q000187:drug effects / Q000502:physiology; D001862:Bone Resorption / Q000503:physiopathology / Q000517:prevention & control*; D006811:Humerus / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013026:Space Flight; D013047:Specific Pathogen-Free Organisms; D013977:Tibia / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D016474:Weight-Bearing; D014893:Weightlessness
chemical_list: D007334:Insulin-Like Growth Factor I