LONG-BONE BIOMECHANICS IN MICE SELECTED FOR BODY CONFORMATION

Two lines of mice divergently selected from the control strain (CBi) a gainst the positive phenotypic correlation between body weight (b.w.) and tail (skeletal) length were obtained (CBi/C: high weight, short ta il; CBi/L: low weight, long tail), The selected animals showed a diffe rent relationship between body and skeletal masses, To compare the ade quacy between biomass and load-bearing ability of the skeleton, and to describe the eventual role of bone mechanostat in the production of t hese changes, cross-sectional and bending properties of both femur dia physes were determined in CBI, CBi/C, and CBi/L adult mice of both gen ders, Cortical bone material quality (elastic modulus) was reduced in the selected lines (p < 0.001), significantly less in CBi/C than in CB i/L, In contrast, cross-sectional design (b.w.-adjusted values of mome nt of inertia, CSMI) was largely improved (p < 0.001), significantly m ore in CBi/C than in CBi/L, These effects determined a greater stiffne ss and strength in CBi/C than in CBi/L or CBi weight-paired mice, The elevations of the negative regression lines between elastic modulus an d CSMI (''distribution/quality'' curves) decreased in the order CBi/C > CBi/L > CBI, Data show that selection improved diaphyseal stiffness and strength in CBi/C animals because of an architectural overcompensa tion for the reduced bone material quality, Therefore, an inadequate c ontrol of longbone architectural design as a function of the mechanica l quality of cortical bone and b.w. bearing could have been induced in that line, Assuming bone mechanostatic regulation to be genetically p rogrammed, some of the corresponding biological determinants should be transmitted independently, because artificial selection separately af fected material quality and architectural design, The possibility of t ransmission of an inadequate mechanostatic function (inability to adap t bone modeling to bone material quality as a function of the biomass to be supported) was also shown, as some genotypes could express archi tectural modifications that largely exceed bone material quality deter ioration. (C) 1997 by Elsevier Science Inc.