Animal housing influences the response of bone to spaceflight in juvenile rats

1 Life Sciences Division, National Aeronautics and Space Administration Ames Research Center, Moffett Field 94035-1000; 2 Department of Medicine, University of California, and Division of Endocrinology, Veterans Affairs Medical Center, San Francisco, California 94121; 3 Departments of Oral Facial Development and Physiology/Biophysics, Indiana University School of Dentistry, Indianapolis, Indiana 46202; and 4 Mineralized Tissues Research Section, Hospital for Special Surgery, New York, New York 10021 The rat has been used extensively as an animal model to study the effects of spaceflight on bone metabolism. The results of these studies have been inconsistent. On some missions, bone formation at the periosteal bone surface of weight-bearing bones is impaired and on others it is not, suggesting that experimental conditions may be an important determinant of bone responsiveness to spaceflight. To determine whether animal housing can affect the response of bone to spaceflight, we studied young growing (juvenile) rats group housed in the animal enclosure module and singly housed in the research animal holding facility under otherwise identical flight conditions (Spacelab Life Science 1). Spaceflight reduced periosteal bone formation by 30% ( P