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

The rat has been used extensively as an animal model to study the effects o f spaceflight on bone metabolism. The results of these studies have been in consistent. On some missions, bone formation at the periosteal bone surface of weight-bearing bones is impaired and on others it is not, suggesting th at experimental conditions may be an important determinant of bone responsi veness to spaceflight. To determine whether animal housing can affect the r esponse of bone to spaceflight, we studied young growing (juvenile) rats gr oup housed in the animal enclosure module and singly housed in the research animal holding facility under otherwise identical flight conditions (Space lab Life Science 1). Spaceflight reduced periosteal bone formation by 30% ( P < 0.001) and bone mass by 7% in single-housed animals but had Little or n o effect on formation (-6%) or mass (-3%) in group-housed animals. Group ho using reduced the response of bone to spaceflight by as much as 80%. The da ta suggest that housing can dramatically affect the skeletal response of ju venile rats to spaceflight. These observations explain many of the discrepa ncies in previous flight studies and emphasize the need to study more close ly the effects of housing (physical-social interaction) on the response of bone to the weightlessness of space flight.