Vertebral bone resorption in vitro: Effects of parathyroid hormone, calcitonin, 1,25 dihydroxyvitamin D₃, epidermal growth factor, prostaglandin E₂, and estrogen

We have developed and characterized a new bone resorption system to test the effect of estrogen on vertebral bone in vitro. Neonatal mouse vertebral bones prelabeled with⁴⁵Ca were maintained in stationary tissue culture for 60-108 hours at 37°C in 5% CO₂/air. Each vertebral bone measured approximately 1 mm×1 mm. Hormonal treatments were added directly to the incubation medium. The morphological appearance of these bones, before and after the onset of resorption, was examined by scanning electron microscopy. Bone resorption was measured by determining the % of the bone⁴⁵Ca released into the incubation medium. Vertebral bone resorption was stimulated in a dose-dependent manner by parathyroid hormone (1-100 nM), 1,25 dihydroxyvitamin D₃ (0.0325-3.25 nM), and prostaglandin E₂ (3-3000 nM). Epidermal growth factor (300 ng/ml) produced a small stimulation of bone resorption which was not inhibited by indomethacin (0.5 μM). Likewise, indomethacin (0.5 μM) did not inhibit PTH-stimulated vertebral bone resorption. Calcitonin (6.6 nM) produced a 79% inhibition of bone resorption induced by PTH (10 nM), whereas estradiol (up to 3 μM) did not inhibit bone resorption. Our results demonstrate that estrogen does not have a direct effect on vertebral bone tissue in vitro. This new bone culture system is a sensitive assay for the direct effects of resorptive agents on vertebral bone.