SPACE-RELATED BONE-MINERAL REDISTRIBUTION AND LACK OF BONE MASS RECOVERY AFTER REAMBULATION IN YOUNG-RATS

This study reports the effects of a 14-day spaceflight followed by a 1 4-day reambulation period on bones of 56-day-old male rats compared wi th synchronous (S) and vivarium (V) control animals. Femur, tibia, and humerus bane mineral densities (BMD); bone calcium and phosphorus con centrations ([Ca2+] and [P]), measured by X-ray microanalysis (XRM), o n tibia, vertebra, and calvaria; and histomorphometric data on proxima l primary and secondary spongiosae (I and II SP, respectively) of the tibia and humerus were measured. After the flight in flown rats (compa red with S), BMD was lost er in the distal femur and remained similar to S in humerus and tibia, [Ca2+] and [P] were lower in tibia II SP an d higher in calvaria, tibia I SP width and II SP bone volume were lowe r, resorption was markedly higher in tibia II SP, and no difference in formation parameters was observed. After reambulation, BMD was lower in long bones of both flight and S groups compared with V. Bone lass a ppeared in humeral II SP and worsened in tibial II SP in flown rats. T ibial formation parameters were higher in flown rats compared with V a nd S, indicating the onset of an active recovery. Tibial XRM [Ca2+] an d [P] in flown rats remained below control levels.