Simulated weightlessness and bone metabolism: decreases of protein and DNA syntheses in the femoral diaphysis of rats.

The effect of simulated weightlessness on bone protein and DNA syntheses was investigated in the skeletal unloading for up to 4 days. The skeletal unloading was designed by using the model of hindlimb hang in rats. The femoral-diaphyseal fragments obtained from rats which bred with skeletal unloading were cultured for 3 h at 37 degrees C in 5% CO2/95% air in Dulbecco's Modified Eagle Medium (high glucose). When the bone tissues were pulsed with [3H]proline, the incorporation of [3H]proline into the bone protein was significantly decreased by skeletal unloading. In the pulse with [14C]uridine, the incorporation of [14C]uridine into the bone RNA was significantly reduced by skeletal unloading. Moreover, the incorporation of [3H]thymidine into the acid-insoluble residues of bone tissue was significantly decreased by skeletal unloading. Also, DNA content in the femoral diaphysis was significantly reduced by skeletal unloading. These findings suggest that skeletal unloading causes the decreases of protein and DNA syntheses in the femoral diaphysis of rats.