Effects of h‐PTH on cancellous bone mass, connectivity, and bone strength in ovariectomized rats with and without sciatic‐neurectomy

The purpose of this study was to determine whether h-PTH (1-34) treatment would recover cancellous bone connectivity and bone strength in ovariectomized (OVX) or ovariectomized and sciatic-neurectomized (OVX+NX) rats. Seven-month-old female Wistar rats were treated with h-PTH or vehicle (6.0 microg/kg, six times a week, subcutaneously) for four weeks beginning 4, 8, or 12 weeks after OVX or OVX+NX. These were compared to age-matched baseline and sham-operated groups. Right tibiae were used for bone histomorphometry and node-strut analysis, and left tibiae were used for mechanical testing. The bone formation rates in the OVX and OVX+NX rats treated with h-PTH were significantly higher than those in their baseline controls. h-PTH treatment increased the node numbers and failure energies in the OVX rats, compared to their baseline controls, at all time points. However, in the OVX+NX rats, the effects of h-PTH treatment on the node number and failure energy were observed only at four weeks after surgery, but not at eight weeks or 12 weeks after surgery. These results suggest that the lowest limit, at which trabecular connectivity and bone strength are able to be restored by h-PTH, occurred between four and eight weeks in OVX+NX rats, but not in OVX rats. h-PTH cannot recover trabecular connectivity and bone strength in advanced osteopenia.