Abstract
This study investigated the effects of a 14-day spaceflight on bone mass, density and microarchitecture in weight bearing (femur and humerus) and non-weight bearing (2nd lumbar vertebra and calvarium) bones in the context of ovarian hormone insufficiency. 12-week-old Fisher 344 rats were ovariectomized 2 weeks before flight and randomized into one of three groups: 1) baseline (n = 6), 2) ground control (n = 12) or 3) spaceflight (n = 12). Additional ground-based ovary-intact rats provided age-matched reference values at baseline (n = 8) and landing (n = 10). Ovariectomy resulted in bone- and bone compartment-specific deficits in cancellous bone volume fraction. Spaceflight resulted in lower cortical bone accrual in the femur but had no effect on cortical bone in the humerus or calvarium. Cancellous bone volume fraction was lower in flight animals compared to ground control animals in lumbar vertebra and distal femur metaphysis and epiphysis; significant differences were not detected in the distal humerus. Bone loss (compared to baseline controls) in the femur metaphysis was associated with lower trabecular number, whereas trabecular thickness and number were lower in the epiphysis. In summary, the effect of spaceflight on bone microarchitecture in ovariectomized rats was bone-and bone compartment-specific but not strictly related to weight bearing.
Highlights
As in humans, the impact of spaceflight on the skeleton of animals has been highly variable[5]
We evaluated the effects of this 14-day spaceflight on bone growth, gene expression and bone turnover in sexually mature but slowly growing ovx rats
The suppressive effects of spaceflight on cortical bone formation in the tibial diaphysis contrasted with a lack of an effect on cancellous bone formation in the proximal tibial metaphysis
Summary
The impact of spaceflight on the skeleton of animals has been highly variable[5]. Factors known to influence the skeletal response to dynamic mechanical loading[11,12] These hormones are important regulators of bone growth and turnover[13] and are often reduced in rats following spaceflight or simulated spaceflight[14,15,16]. Because evaluation of bone microarchitecture in this study was limited to the tibia, it is not clear whether the observed effects are generalizable to other skeletal sites In this follow-up study, we took advantage of archived specimens obtained from the STS-62 mission to evaluate the combined effects of the spaceflight and ovx-induced gonadal hormone depletion on bone mass, density and microarchitecture in representative bones from the appendicular weight bearing (femur and humerus) and axial non-weight bearing (lumbar vertebra and calvarium) skeleton
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