The comparative effects of dichloromethylene diphosphonate (C12MDP) and ethane-1-hydroxy-1,1-diphosphonate (EHDP) on growth and modeling of the rat tibia.

Male rats weighing 100 g were assigned to groups and injected daily for 10 days with vehicle (control), 0.4, 2.0, 4.0, 10.0, or 20.0 mg/kg/day of ethane-1-hydroxy-1,1-diphosphonate (EHDP) or dichloromethylene diphosphonate (C12MDP). The proximal tibial metaphysis and epiphysis were assayed for changes in percentage of hard tissue and bone formation parameters. From the data, information about hard tissue resorption was deduced. All doses of C12MDP and doses of 2.0 mg EHDP/kg/day and greater caused significant increases in percentage of hard tissues with C12MDP being more effective than similar doses of EHDP in decreasing bone resorption. Osteoclast population parameters were increased with all doses of both C12MDP and EHDP with C12MDP having a greater effect than similar doses of EHDP. Decreases in the proliferation of the osteoprogenitor pool parallel the decreases in osteoblasts and bone formation parameters. These decreases in osteoprogenitor pool proliferation do not account for the increases with diphosphonates in osteoclast population parameters.