Materials and methods. – Thirty-six female Wistar rats aged 12 weeks were randomized to bilateral surgical ovariectomy without tail suspension (OV) or with tail suspension for 30 days (OV-TS) or to sham surgery without tail suspension (control group, C) or with tail suspension for 30 days (TS). Bone mineral density (BMD) of the distal femoral metaphysis was measured in g/cm2 by dual X-ray absorptiometry in all 12 animals on days 0, 7, 14, and 30.
Results. – On D14 and D30, BMD (mean ± S.D.) was significantly lower in the OV, TS, and OV-TS groups than in the control group (D14: 0.239 ± 0.014, 0.243 ± 0.016, and 0.227 ± 0.018, respectively, vs. 0.258 ± 0.005 in the controls; P < 0.05; and D30: 0.241 ± 0.011, 0.227 ± 0.015, and 0.200 ± 0.018, respectively, vs. 0.279 ± 0.009 in the controls; P < 0.001). On D30, the percentage BMD change versus baseline (mean ± S.D.) differed significantly between the combination (OV-TS) group (−14.26 ± 8.14) and the single-intervention groups (OV: +0.99 ± 6.44, P < 0.001; and TS: −6.36 ± 4.56, P < 0.05). As early as D7, bone loss was significantly greater in the combination (OV + TS) group than in the OV group (−1.79 % ± 7.17 vs. +4.29 % ± 9.55; P < 0.05).
Conclusion. – In female rats, the rate and severity of bone loss were greater when estrogen deprivation was combined with mechanical unloading than when either intervention was used alone. Mechanical unloading induced a greater degree of bone loss than did estrogen deprivation. In this model of high-rate bone loss, mechanical unloading may predominate over estrogen deprivation in the genesis of bone loss.