Effects of space flight on bone formation and resorption.

Samples of femurs and tibiae of male Wistar rats subjected to a 13 day space-flight on the biosatellite Cosmos 1887--were investigated and compared with vivarium and synchronous controls or immobilized rats, using histological and histomorphometric methods. 1. After flight in the metaphysis of bones the density and volume of the spongious trabeculae diminished significantly indicated by the Sv and Vv histomorphometric values and histological data comparing to the controls. In the diaphysis, the density of trabeculae decreased too. 2. In the flight group significant suppression of bone formation was determined by histological and histomorphometric (decrease of the OS, OB and OBI values) methods. 3. In the flight group according to the histological pictures the signs of bone resorption (increase of Hoswship's lacunae, osteoclastic activity, structural rarefication of spongious and cortical bones, osteon disintegration, osteocytic osteolysis) were revealed, which was substantiated by the histomorphometric results (increase of osteoclastic index: OCI). 4. Significant differences between flight and immobilized groups were not determined, except the osteoid value, which was increased in the case of immobilization. 5. Some histomorphometric values related to bone formation of synchronous control group showed close relationship rather to the flight group than to the vivarium control group.