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First published online January 31, 2007
Journal of Experimental Biology 210, 602-613 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02675

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Variation in estradiol level affects cortical bone growth in response to mechanical loading in sheep

Maureen J. Devlin^* and Daniel E. Lieberman

Department of Anthropology, Peabody Museum, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA

^* Author for correspondence (e-mail: mdevlin{at}fas.harvard.edu)

Accepted 29 November 2006

Although mechanical loading can stimulate cortical bone growth, little is known about how individual physiology affects this response. This study demonstrates that in vivo variation in estradiol (E₂) level alters osteoblast sensitivity to exercise-induced strains, affecting cortical bone responses to mechanical loading. Subadult sheep were divided into treatment groups that varied in terms of circulating E₂ levels and loading (exercised and sedentary). After 45 days, periosteal cortical bone growth rates and cross-sectional properties were measured at the midshafts of hindlimb bones and compared with strain data. The results indicate significant interactions between E₂ and strain. Cortical bone growth in exercised animals with elevated E₂ levels was 27% greater in the femur, 6% greater in the tibia, and 14% greater in the metatarsal than in exercised animals with lower E₂ levels, or sedentary animals regardless of E₂ dose (P<0.05). There was also a trend toward greater resistance to deformation in the tibia, but not the metatarsal, in the exercised, high-E₂ group compared to the other treatment groups. These results demonstrate that E₂ plays a role in mediating skeletal responses to strain, such that physiological variation in E₂ levels among individuals may lead to differential growth responses to similar mechanical loading regimes. Efforts to model the relationship between environmental strain and bone morphology should include the effects of physiological variation in hormone levels.

Key words: bone, estradiol, estrogen receptor-alpha, periosteal modeling, sheep, strain

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