Differential effect of short-term etidronate treatment on three cancellous bone sites in orchidectomized adult rats

The aim of the present study was to analyze the effects of short-term treatment with the antiresorptive agent, etidronate, on orchidectomized adult rats, via comparison of three cancellous bone sites, the lumbar vertebral body (LVB), proximal tibial metaphysis (PTM), and distal tibial metaphysis (DTM). Thirty-five male Wistar rats, aged 10 months, were randomly divided into four groups: baseline control (BLC, nF10), age-matched sham-operated control (AMC, nF9), orchidectomy (ORX, nF9), and ORXBetidronate treatment (nF7). Etidronate treatment (10 mg/kg, daily subcutaneous injection) was initiated 2 weeks after surgery and was continued for 2 weeks. Four weeks after surgery, the 5th LVB, PTM, and DTM were processed for histomorphometric analysis of cancellous bone (secondary spongiosa). ORX resulted in a decrease in body weight. No significant difference in cancellous bone volume (BV/TV) was found between the BLC and AMC groups at any skeletal site. The cancellous BV/TV loss was attributable to increased eroded surface (ES/BS) with no significant alteration in the mineral apposition rate (MAR), at all skeletal sites and etidronate treatment in ORX rats significantly decreased ES/BS to a level not significantly different from that in the AMC group, resulting in complete prevention of ORX-induced cancellous BV/TV loss. The MAR was markedly decreased in the PTM and LVB, but maintained in the DTM by etidronate treatment. The present study showed that etidronate treatment could completely prevent ORX-induced cancellous bone loss regardless skeletal sites by suppressing bone resorption. In particular, suppression of bone formation in terms of osteoblastic activity by etidronate treatment was not evident only in the DTM