LONG-TERM EFFECTS OF CLODRONATE ON GROWING RAT BONE

For evaluating the long-term effects of the bisphosphonate compound cl odronate on the rat skeleton, 100 female rats were given subcutaneous injections of clodronate at doses of 0 (vehicle), 4 (low), or 12 (high ) mg/kg per week, or 50 mg/kg every fourth week (cyclical), The treatm ent was started at 3 months of age and was continued for 6 months, The mechanical strength of bones was studied by torsion of the tibia, thr ee-point bending of the femur, axial compression of the femoral neck, and compression of a Lumbar vertebra, Quantitative histomorphometric v ariables were determined from distal femur and lumbar vertebra, and va riables reflecting bone metabolism were measured in serum and urine, B one mass, indicated by ash weight of the tibia, was increased with the low and high clodronate doses compared with the vehicle, The maximum load in vertebra compression was increased with the low dose of clodro nate compared with the vehicle, whereas changes in other variables con cerning bone strength were not significant, In bone histomorphometry, clodronate treatment induced more pronounced changes in cancellous bon e volume in distal femur than in lumbar vertebra, the differences not being statistically significant between the groups at either site, how ever. The longitudinal growth rate of the femur, measured by double-fl uorochrome labeling for 1 week at the end of the treatment period, was significantly decreased in the high-dose clodronate group compared wi th the other groups, Serum values for calcium, tartrate-resistant acid phosphatase, and alkaline phosphatase did not differ between the grou ps, However, serum osteocalcin was significantly lower in the high-dos e group compared with the vehicle group, Urinary calcium, hydroxyproli ne, and hydroxylysylpyridinoline were decreased at all the clodronate doses administered, In conclusion, the beneficial effects of long-term clodronate treatment on bone mass and strength were observed at the l owest dose used, A high dose of clodronate decreased bone growth rate, which was, however, not reflected in the mechanical quality of bone.