EFFECTS OF SPACEFLIGHT AND RECOVERY ON RAT HUMERI AND VERTEBRAE - HISTOLOGICAL AND CELL-CULTURE STUDIES

Skeletal changes associated with spaceflight in the rat have been well documented, but few data are available on bone tissue and bone cell m etabolism after subsequent on-Earth recovery. We therefore investigate d the effects of microgravity and subsequent recovery on trabecular bo ne morphology and cellular activities in rat humeri and thoracic verte brae and compared histomorphometric parameters in caudal vertebrae wit h the behavior of vertebral osteoblastic cells in culture. We report h ere that humeral weight showed normal growth during the experiment but was unaffected by spaceflight or recovery from spaceflight. However, the 14-day spaceflight resulted in inhibition of static indexes of bon e formation in humeral proximal metaphyses and thoracic vertebral bodi es. This was associated with a decrease in bone volume in humeral meta physes. After 14 days of on-Earth recovery, osteoblastic and osteoid s urfaces returned toward normal and bone volume was normalized in humer i, whereas the static bone formation parameters were not restored in t horacic vertebrae. In addition, histological indexes of bone formation and osteoblastic cell growth in vitro were not affected by spacefligh t in caudal vertebrae. This study shows that rat humeri and thoracic a nd caudal vertebrae exhibit differ ent patterns of response to spacefl ight and subsequent on-Earth recovery, which could be due, at least in part, to the different loading pattern of these bones, and also to di fferences in bone turnover rate.