Female Sprague Dawley rats were subjected to either bilateral ovariectomy or sham surgery. Tetracycline derivatives were administered to each rat on two separate occasions to label sites of bone formation. All rats were sacrificed at 5 weeks postovariectomy and their proximal tibiae were processed undecalcified for quantitative bone histomorphometry. A twofold decrease in trabecular bone volume was noted in the proximal tibial metaphysis of ovariectomized rats. This bone loss was associated with elevated histomorphometric indices of bone resorption and formation. Ovariectomy increased osteoclast surface and numbers as well as osteoblast surface and numbers. Elevations in calcification rate and fractional trabecular bone surface with double tetracycline labels also suggest that bone formation was stimulated in ovariectomized rats. In addition, ovariectomized rats exhibited a greater rate of longitudinal bone growth relative to sham-operated control rats. These histomorphometric data indicate that ovariectomy induces marked bone loss and accelerated skeletal metabolism in rats.
Male Sprague-Dawley rats were placed in orbit for 7 days aboard the space shuttle. Bone histomorphometry was performed in the long bones and lumbar vertebrae of flight rats and compared with data derived from ground-based control rats. Trabecular bone mass was not altered during the 1st wk of weightlessness. Strong trends were observed in flight rats for decreased periosteal bone formation in the tibial diaphysis, reduced osteoblast size in the proximal tibia, and decreased osteoblast surface and number in the lumbar vertebra. For the most part, histological indexes of bone resorption were normal in flight rats. The results indicate that 7 days of weightlessness are not of sufficient duration to induce histologically detectable loss of trabecular bone in rats. However, cortical and trabecular bone formation appear to be diminished during the 1st wk of spaceflight.
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