CALCITONIN ALTERS BONE QUALITY IN BEAGLE DOGS

Because of its antiresorptive properties, calcitonin is widely used to prevent and treat osteoporosis. A stimulatory effect of calcifonin on osteoblasts has also been reported; however, a recent histologic stud y points to a negative effect of calcitonin on mineralization of cance llous bone, The present experiment was performed to determine whether the observed histological signs of alterations in mineralization are a lso observed in cortical bone and whether this results in changes in m echanical properties, mineral densities, or mineral properties of cani ne bone, Sixteen female adult beagle dogs were randomly allocated to r eceive either human calcitonin at a dose of 0.25 mg/dog (50 IU, n = 5) or vehicle (mannitol, n = 8) every other day for 16 weeks, At the end of the study, fire dogs were euthanized, Both tibiae, L1 and L5 verte brae, and iliac crest bone samples were excised and defleshed, Torsion al mechanical properties of tibial diaphyses and compressive strengths of vertebrae were measured, Bone mineral densities (BMD) of tibiae an d vertebrae were measured by using dual-energy X-ray absorptiometry, U ltrastructural mineral characteristics of iliac crest bone were determ ined by gravimetry and Fourier transform infrared spectroscopy (FTIR). Bone histomorphometry was performed in the cortical envelope of the i liac crest, Tibiae from dogs treated with calcitonin withstood signifi cantly less maximum torque until failure, required less torsional ener gy to reach the maximum torque, and had less torsional stiffness than file tibiae from dogs treated with vehicle (p < 0.05). Cancellous core s of vertebrae from calcitonin-treated dogs withstood less compressive mechanical loading than did vertebral cores from vehicle-treated anim als (p < 0.05), Dogs treated with calcitonin had less BMD of both tibi ae and vertebrae than vehicle-treated animals (p < 0.05), Bones from c alcitonin-treated dogs had significantly less ash content, which corre lated with the lower phosphate-lu-amide I (detected by FTIR) and great er carbonate-to-phosphate ratios than did bones from vehicle-treated d ogs (p < 0.05), Calcitonin-treated dogs exhibited a decrease in bone f ormation and mineralization rates and an increase in mineralization la g time. These results point to a negative effect of calcitonin on bone quality, These findings are intriguing and call for further studies a ddressing whether the observed abnormalities are transient or permanen t.