Quantitative histochemistry of rat lumbar vertebrae following spaceflight

Spaceflight has been shown to cause alterations in bone mineral content, bone growth, and resorption. In this study, the effects of return to gravity immediately and 6 and 29 days following spaceflight on bone of rat vertebral bodies were histochemically analyzed. Immediately postflight, there was no significant change in calcium salt content of the vertebrae, but 6 days later it was significantly decreased (P less than 0.05). By 29 days postflight, the calcium salt content had returned to normal. Postflight collagen content was not significantly altered. Keratosulfate was significantly higher (P less than 0.05) in trabecular bone of rats immediately postflight and 6 days postflight. Chondroitin sulfate was increased in vertebral bone on days 6 and 29 postflight. The histochemical patterns observed in this study suggest that bone turnover slows in vertebrae during spaceflight allowing bone ageing. The results support the contention that a form of osteolysis begins, immediately upon return to gravity, to remove components of old bone at which time mineral levels do decrease and levels of chondroitin and keratosulfates shift. The osteolysis phase is quickly followed by new bone replacement which is completed before 29 days postspaceflight.