LACK OF EFFECT OF SPACEFLIGHT ON BONE MASS AND BONE-FORMATION IN GROUP-HOUSED RATS

As part of an experiment to study the role of corticosteroids in bone changes during spaceflight, male Sprague-Dawley rats (6 wk old, 165 g body weight) were placed in orbit for 17 days, in groups of six, in an imal-enclosure modules (AEMs) aboard the space shuttle Columbia (STS-7 8). Control rats were group housed in a similar manner in ground-based AEMs or standard vivarium cages. Adrenal hypertrophy occurred in flig ht rats, but bone histomorphometric analyses revealed a lack of signif icant changes in bone mass and bone formation in these animals. Cancel lous bone volume and osteoblast surface in the proximal tibial metaphy sis were nearly the same in flight and ground-based rats. Normal level s of cancellous bone mass and bone formation were also detected in the lumbar vertebrae and femoral necks of flight rats. In the tibial diap hysis, periosteal bone formation rate was found to be identical in fli ght and ground-based rats. The results indicate that, under conditions of group housing in AEMs, spaceflight has minimal effects on bone mas s and bone formation in rapidly growing rats. These findings emphasize the need to investigate the importance of rat age, strain, and especi ally housing conditions for studies of the skeletal effects of spacefl ight.