Collagen and mineral kinetics in bone after fracture

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Abstract
The rates of collagen synthesis and mineral formation were studied in intact and fractured bones. The right tibia was fractured in adult female rats and each rat was injected with a combined tracer dose of 47ca, 48Ca, and L-14C-proline at intervals ranging from 1 to 21 days after fracture. The rats were killed 24 hr. after injection of the tracers, and the specific activities of Ca and of hydroxyproline in fractured and intact bones were determined. The specific activity values were interpreted to reflect the relative rates of mineral accretion and collagen synthesis, respectively. In intact bone a close correlation was observed between these rates. At the fracture site, however, there was a wide divergence between the rates of mineral accretion and collagen synthesis. The difference reached a maximum 7 days after fracture, at which time the hydroxyproline specific activity ratio, fractured-to-intact bone, was about 7 times higher than the corresponding Ca specific activity ratio. After the 7th day, the hydroxyproline specific activity ratio decreased sharply, whereas the Ca specific activity ratio continued to increase until 21 days after fracture when these 2 ratios became equal. Under normal steady-state conditions the general pattern of bone tissue synthesis is the same, whether one studies the mineral or the collagen phases. In nonsteady-state conditions, when the proportion of mineral to collagen in bone is changing, different rates of synthesis are observed and studies of only 1 phase will not reflect the metabolism of the bone tissue as a whole.

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