Influence of Early and Late Zoledronic Acid Administration on Vertebral Structure and Strength in Ovariectomized Rats

An annual infusion of zoledronic acid (ZOL) reduces fracture riskin osteoporotic patients. Previously, we showed that a single ZOL injection inhibited changes in bone microstructure and strength in rat tibiae after ovariectomy. Here, we determined the effects of a single ZOL injection as preventive and restorative treatment on the bone micro-structure and strength in lumbar and caudal vertebrae of ovariectomized (OVX) rats. Twenty-nine female 35-week-old Wistar rats were divided into four groups: SHAM-OVX (n = 9), OVX (n = 7). ZOL was given once (20 mu g/kg body weight s.c.) at OVX. Trabecular and cortical bone microarchitecture were measured in lumbar (L3) and caudal (Cd6) vertebrae using micro-computed tomography, and compressive mechanical properties were determined in L3 vertebrae. Compared to SHAM-OVX, OVX rats had significantly lower BV/TV; SMI, Tb.N, Tb.Sp, and Conn.D tended to be deteriorated in lumbar vertebrae, while both ZOL groups did not differ from the SHAM-OVX group. Both ZOL groups had significantly higher BV/TV than OVX; the early ZOL group also had significantly lower SMI and higher Tb.Th. OVX tended to decrease mechanical properties, while early and late ZOL treatment inhibited OVX-inducible degeneration. Neither OVX nor ZOL induced changes in the trabecular microarchitecture of caudal vertebrae. In summary, in adult rats a single ZOL injection inhibited OVX-induced changes in lumbar vertebral bone microarchitecture and strength.