Bone, Calcium, and Space Flight

Bone and calcium physiology

Rattus norvegicus (Sprague-Dawley rat)
Flight: 12 Male

Basal: 6, Synchronous: 12, Vivarium: 12

Research Animal Holding Facility

The objectives of this experiment were: 1) to determine if exposure to microgravity causes a significant decrease in bone mineralization at the outer surface of limb bones within the first week of flight and to assess those bone parameters causing or affected by this decrease; 2) to measure activity of osteoblast immediately postflight; 3) to determine if bone mineralization is restored following 2 weeks of recovery from space flight; 4) to determine total skeletal and site-specific bone mineralization rates, mineralization and resorption, as well as calcium absorption and excretion; 5) to relate effects of microgravity on bone to changes in calcium metabolism; and 6) to determine gut and renal responses during postflight recovery period.

Body mass, blood pH, and urine volume were measured. Upon sacrifice, the vertebrae, maxillae, tibias, femurs, humeri, calvaria were removed and processed. Bone samples were analyzed for bone mineralization rates, alkaline phosphatase activity, bone dimensions, osteoblast populations, matrix and mineral content, and biomechanics. Ca and crosslink content was determined for the urine as well as bone samples. Bone samples were also analyzed under electron microscopy and 3-D X-ray topographic microscopic images.

Ionic calcium and pH were similar in all groups at the end of the flight period, suggesting that any changes induced by flight had returned to normal prior to the time that the animals were sacrificed. All groups had similar bone length in both front and hindlimbs as well as in the jaw. Bone mineralization on the periosteal surface at the tibiofibular junction was suppressed in the flight rats during the flight period and did not return to normal until the second week of the recovery period. Alkaline phosphatase activity, a marker of bone matrix maturation, was suppressed in the endosteal osteoblast immediately postflight and at 2 weeks post-recovery. This data suggest that bone response to unloading and reloading may be different at different bone sites. Urinary collagen crosslinks were slightly decreased following flight, suggesting that resorption was not dramatically effected during the recovery period. Surprisingly, very few significant changes in bone were noted in these very young, rapidly growing rats (38 days old at launch).

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