EFFECTS OF CLODRONATE ON CORTICAL AND TRABECULAR BONE IN OVARIECTOMIZED RATS ON A LOW-CALCIUM DIET

The aim of this study was to evaluate the contribution of a low calciu m diet to the cortical and trabecular osteoporosis seen in ovariectomi zed rats after 7 weeks on a low calcium diet and to investigate the ef fects of the bisphosphonate clodronate on this development of osteopor osis. Thirty-six mature, female Wistar rats were randomized into four groups: Ovx-B (bisphosphonate) and Ovx-C (control) were ovariectomized , and Sham-Ca (low calcium) and Sham+Ca (normal calcium) were sham ope rated. The first three groups were fed a low calcium diet (0.01%) and Sham+Ca normal rat chow (Ca 1.1%). The Ovx-B received 10 mg/kg s.c. cl odronate daily for nine weeks, and Ovx-C, Sham-Ca, and Sham+Ca receive d the same volumes of saline. Bone mineral turnover measured as Sr-85- uptake was increased in all low calcium groups compared to Sham+Ca. Th e Sham+Ca femora had higher dry weight and ash weight than the other g roups, and Ovx-C had higher dry weight compared with Ovx-B and Sham-Ca , Calcium content was lower in both Ovx groups compared to both Sham g roups. Magnesium was lower in all groups compared to Sham+Ca and highe r in Ovx-B compared with Ovx-C. In the femoral shaft, Sham+Ca had sign ificantly higher ultimate bending moment, energy absorption, and defle ction compared to the other three groups. Ultimate bending moment was higher in Sham-Ca than in Ovx-C. Stiffness was increased in both ShamCa and Ovx-B compared to Ovx-C. The maximum stress in the femoral mids haft was higher in Sham+Ca than in the other groups, and higher in Ovx -B than in Ovx-C. Histomorphometry showed increased medullary area in all low calcium groups compared to Sham+Ca and larger cortical area in Sham+Ca and Ovx-B compared to Ovx-C. Compared to Sham+Ca the trabecul ar bone volume was decreased to 30% in Sham-Ca and to 9% in Ovx-C, but was unchanged in Ovx-B, The low calcium diet generally increased bone mineral turnover and reduced the tibial bone volume. Femoral changes led to a reduction of cortical fracture strength and maximal stress, O variectomy in addition to a low calcium diet reduced femoral strength even more. Daily injections of clodronate to ovariectomized rats on a low calcium diet increased femoral shaft stiffness and maximum stress, and clodronate preserved both trabecular and cortical tibial bone vol ume completely.