HISTOMORPHOMETRIC ANALYSES OF CANCELLOUS BONE FROM COSMOS-2044 RATS

The influence of 14 days of spaceflight on cancellous bone of male Wis tar rats was assessed by histomorphometric analysis. In proximal tibia , no difference was found between flight, synchronous, vivarium, and b asal groups for epiphyseal bone volume or trabecular arrangement. In m etaphysis, primary spongiosa width was reduced in flight rats, suggest ing an alteration in bone longitudinal growth. In flight rats, seconda ry spongiosa evidenced a trend toward decreased bone mass, trabecular number and thickness, and osteoid surfaces, whereas there was a tenden cy toward increased osteoclast number compared with vivarium control b ut not with synchronous rats. In femoral fossa trochanteri, an area fa cing deep muscular insertions, no changes in bone volume or structure were noted among the different groups. However, a reduction of osteoid surfaces was seen in flight and synchronous groups compared with the other groups. Resorption activity was increased in flight rats compare d with control rats. In thoracic vertebral body, osteoblastic surfaces decreased similarly in flight and synchronous rats. In lumbar vertebr al body, decreased osteoblastic surfaces and increased osteoclastic pa rameters were observed in flight and synchronous rats. The more striki ng effects of spaceflight were the decrease in tibial primary spongios a width and the increase in resorption activity of the femoral fossa t rochanteri. In all other sites, cellular alterations appeared similar in flight and synchronous rats, suggesting a role for physiological st ress. The time course of events would depend on initial growth and tur nover rates of bone, its weight-bearing function on earth, and the pre sence of muscular insertions.