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First published online October 27, 2003

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The Journal of Experimental Biology 206, 4233-4239 (2003)
doi: 10.1242/jeb.00671

Bone formation is not impaired by hibernation (disuse) in black bears Ursus americanus

Seth W. Donahue^1,*, Michael R. Vaughan², Laurence M. Demers³ and Henry J. Donahue⁴

¹ Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931, USA
² US Geological Survey, Virginia Cooperative Fish and Wildlife Research Unit, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, USA
³ Departments of Pathology and Medicine
⁴ Department of Orthopaedics and Rehabilitation, The Pennsylvania State University, Hershey, PA 17033, USA

^* Author for correspondence (e-mail: swdonahu{at}mtu.edu)

Accepted 15 August 2003

Disuse by bed rest, limb immobilization or space flight causes rapid bone loss by arresting bone formation and accelerating bone resorption. This net bone loss increases the risk of fracture upon remobilization. Bone loss also occurs in hibernating ground squirrels, golden hamsters, and little brown bats by arresting bone formation and accelerating bone resorption. There is some histological evidence to suggest that black bears Ursus americanus do not lose bone mass during hibernation (i.e. disuse). There is also evidence suggesting that muscle mass and strength are preserved in black bears during hibernation. The question of whether bears can prevent bone loss during hibernation has not been conclusively answered. The goal of the current study was to further assess bone metabolism in hibernating black bears. Using the same serum markers of bone remodeling used to evaluate human patients with osteoporosis, we assayed serum from five black bears, collected every 10 days over a 196-day period, for bone resorption and formation markers. Here we show that bone resorption remains elevated over the entire hibernation period compared to the pre-hibernation period, but osteoblastic bone formation is not impaired by hibernation and is rapidly accelerated during remobilization following hibernation.

Key words: black bear, Ursus americanus, bone formation, hibernation, metabolism, adaptation, collagen, disuse

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