Effects of intermittent administration of low dose human PTH(1–34) on cancellous and cortical bone of lumbar vertebral bodies in adult beagles

This study assessed the effect of low dose human parathyroid hormone [hPTH(1–34)] administration on cancellous and cortical bone of lumbar vertebrae in intact male beagles. 16 19–20-month-old beagle dogs were randomized into four groups: in group 1, the vehicle control group, saline was injected daily; in group 2, the sequential group, 0.375 μg/kg of PTH was injected daily for 4 weeks, then off 8 weeks, and this sequence was once repeated for another 4 and 8 weeks; in group 3, the same dose of PTH was injected once per week for 24 weeks; and, in group 4, PTH was injected three times per week for 24 weeks. Histomorphometric assessment on cancellous and cortical bone (both ventral and dorsal shell) and two-dimensional node-strut analysis were done on the fifth lumbar vertebral bodies after calcein double bone labeling. In intact adult beagles, on the group treated with 0.375 μg/kg per day three times per week (group 4): (1) had a higher mean value in cancellous bone formation parameters [osteoid surface (+74%), osteoid volume (twofold), mineral apposition rate (+21%), and bone formation rate (two-fold)]; (2) exhibited no effect on cortical thickness and porosity in both the ventral and dorsal shell; and (3) showed a lower mean value of node to termini (0.11 ± 0.02 vs. 0.22 ± 0.09) and a higher mean value of cortex to node (0.18 ± 0.06 vs. 0.08 ± 0.02), but not in trabeculae to trabeculae node, than age-related controls. In conclusion, we found that a low dose of PTH administration: (1) stimulated cancellous bone formation; (2) improved connectivity of trabeculae joined to the cortex; (3) did not decrease cortical thickness; and (4) did not increase cortical porosity in both ventral and dorsal cortexal shell of the lumbar vertebrae during this dosage and period in intact male beagles.