We compared the effects of intermittent administration of human parathyroid hormone (PTH) (1-34) on tibial cancellous and cortical bone loss in tail-suspended and sciatic neurectomized young rats. Forty-eight 6-week-old male Wistar rats were randomly divided into six groups with eight animals each: age-matched controls (AMC), tail suspension (TS), sciatic neurectomy (NX), AMC + PTH, TS + PTH, and NX + PTH. Fifteen days after the start of the experiment, the proximal tibia and tibial shaft were processed for cancellous and cortical bone histomorphometric analyses, respectively. The reduction of cancellous bone volume (BV/TV) was significantly greater in the TS group than in the NX group, whereas the reduction of percent cortical area (Ct Ar) did not differ significantly between the TS and NX groups. Administration of human PTH to rats in the TS and NX groups increased BV/TV to a level significantly higher than that of the AMC group. Administration of human PTH to rats in the NX group significantly increased percent Ct Ar, but percent Ct Ar of the NX group was still significantly lower than that of the AMC group. Administration of human PTH to rats in the TS group did not significantly affect percent Ct Ar. These findings suggest that intermittent administration of human PTH (1-34) at the dose we used may completely prevent cancellous bone loss both in TS and NX young rats, and that it may not affect cortical bone loss in TS young rats but only attenuate it in NX young rats.
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