Tumor necrosis factor α and interleukin‐1 stimulate bone resorption in vivo as measured by urinary [ 3 H]tetracycline excretion from prelabeled mice

Tumor necrosis factor α (TNF‐α) and interleukin‐1 (IL‐1) have been shown to stimulate bone resorption in vitro. We have now investigated whether these cytokines also cause a similar action when administered in vivo. This was made possible by the adaptation of a newly developed technique that enables the continual assessment of bone resorption in vivo in mice by measuring urinary excretion of 3 H from [ 3 H]tetracycline‐prelabeled animals. Experiments using maneuvers known to influence bone resorption, such as a change in dietary calcium or administration of parathyroid hormone or dichloromethylenebisphosphonate, indicate that the technique is reliable and sensitive in mice. Daily intravenous administration of either recombinant human or recombinant murine TNF‐α, as well as subcutaneous administration of recombinant human IL‐1α, were found to stimulate bone resorption in a dose‐dependent manner. The effect was maximal within 2 days. Thus, exogenous TNF‐α and IL‐1α can stimulate bone resorption in vivo, suggesting that these cytokines may also exert a systemic effect on bone.