³H-tetracycline as a proxy for ⁴¹Ca for measuring dietary perturbations of bone resorption

Our group is interested in evaluating early effects of dietary interventions on bone loss. Postmenopausal women lose bone following reduction in estrogen which leads to increased risk of fracture. Traditional means of monitoring bone loss and effectiveness of treatments include changes in bone density, which takes 6 months to years to observe effects, and changes in biochemical markers of bone turnover, which are highly variable and lack specificity. Prelabeling bone with ⁴¹Ca and measuring urinary ⁴¹Ca excretion with accelerator mass spectrometry provides a sensitive, specific, and rapid approach to evaluating effectiveness of treatment. To better understand ⁴¹Ca technology as a tool for measuring effective treatments on reducing bone resorption, we perturbed bone resorption by manipulating dietary calcium in rats. We used ³H-tetracycline (³H-TC) as a proxy for ⁴¹Ca and found that a single dose is feasible to study bone resorption. Suppression of bone resorption, as measured by urinary ³H-TC, by dietary calcium was observed in rats stabilized after ovariectomy, but not in recently ovariectomized rats