title: The effects of loading and estrogen on rat bone growth.
abstract: This study evaluated the contributions of locomotive loading and estrogen to the development of diaphysis of rat femur. A randomized 2x2 study design was used. Altogether, 70 female Sprague-Dawley rats were used, of which 10 were euthanized at entry. Of the remaining rats, 16 served as controls, and the rest, 44, underwent a unilateral sciatic neurectomy. The effect of estrogen was removed by ovariectomizing one-half of the neurectomized rats. After 27 wk, the animals were euthanized, and the femora were excised. Irrespective of loading or estrogen, the femur length and mineral mass increased by 142 and 687%, respectively. Axial growth was not modulated either by locomotive loading or estrogen, but the loading resulted in direction-specific changes in the cross-sectional geometry. The estrogen-related gains were evident on the endocortical surface, while the loading-related gains occurred on the periosteal surface. The loading and estrogen were significantly associated with increased bone strength (21 and 15%, respectively) in the mediolateral direction, but not in the anteroposterior direction. Axial growth and accrual of bone mineral mass of the rat femur are largely independent of locomotive loading or estrogen, whereas these factors specifically account for the femur function, as either a mechanical lever or a mineral reservoir for reproduction, respectively.
authors.affiliation: Medical School, Institute of Medical Technology, University of Tampere, and Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, Tampere, Finland.
authors.forename: Olli V
authors.initials: OV
authors.lastname: Leppänen
authors.forename: Harri
authors.initials: H
authors.lastname: Sievänen
authors.forename: Jarkko
authors.initials: J
authors.lastname: Jokihaara
authors.forename: Ilari
authors.initials: I
authors.lastname: Pajamäki
authors.forename: Pekka
authors.initials: P
authors.lastname: Kannus
authors.forename: David M
authors.initials: DM
authors.lastname: Cooper
authors.forename: Teppo L N
authors.initials: TL
authors.lastname: Järvinen
mesh_terms: D000818:Animals; D001846:Bone Development / Q000187:drug effects* / Q000502:physiology*; D004967:Estrogens / Q000008:administration & dosage*; D005260:Female; D005269:Femur / Q000187:drug effects* / Q000254:growth & development*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016474:Weight-Bearing / Q000502:physiology*
chemical_list: D004967:Estrogens