Effect of intermittent injection of recombinant human parathyroid hormone on bone histomorphometry of ovariectomized...

To observe the effect of intermittent parathyroid hormone (PTH) administration on bone histomorphology of relatively old ovariectomized rats.

The 6-month-old female SD rats were randomly divided into 5 groups: (1) sham-operated for baseline (ShamB, n=5), (2)ovariectomized for baseline (OVXB, n=6), (3) Sham-operated for end point (ShamE, n=6), (4) ovariectomized for end point (OVXE, n=6), (5) ovariectomized for PTH treatment (OVXEP, n=6). ShamB and OVXB rats were sacrificed 3 months after operation, ShamE, OVXE and OVXEP rats were sacrificed 4.5 months after operation. During 3-4.5 months after operation, OVXEP rats received daily subcutaneous injection of rhPTH1-84, while ShamE and OVXE received vehicle injection. The proximal tibiae of all rats were processed without decalcification for quantitative bone histomorphometry.

The percent trabecular area (TbAr) of OVXEP was significantly greater than that of OVXE (P <0.05), and was similar to that of OVXB (P >0.05), but was smaller than that of ShamE (P <0.05); the trabecular thickness (TbTh) of OVXEP was thicker than any other group (all, P <0.05); the trabecular number (TbN) of OVXEP was only slightly higher than that of OVXE; the percent labeled perimeter (LPm), mineral apposition rate (MAR) and bone formation rate with bone area as referent (BFR/BV) of OVXEP were all higher than those of ShamE and OVXE respectively (P <0.01), whereas the osteoclast number (N of Oc) of OVXEP was similar to those of ShamE and OVXE (P >0.05).

Short-term intermittent injection of rhPTH1-84 can prevent further bone loss in 9-month-old rats 3 months after ovariectomy, the mechanisms of this therapy are that PTH could increase TbTh while not alter TbN, and promote bone-forming activity while not influence bone-resorptive activity.