Individual and combined effects of exercise and alendronate on bone mass and strength in ovariectomized rats

Exercise and bisphosphonate therapies increase bone strength by primarily increasing bone formation and reducing resorption, respectively. Based on these different mechanisms of action, it is possible that combined introduction of exercise and bisphosphonate therapies generates greater improvements in bone mass and strength than either intervention alone. The aim of this study was to examine the individual and combined effects of exercise (treadmill running) and bisphosphonate therapy (alendronate [ALN]) on bone mass and strength in ovariectomized (OVX) rats. Seven-month-old virgin female rats were randomly assigned to either a sham-OVX group (n=13) or one of four OVX groups: vehicle-treated cage-control (VEH-CON, n=10); ALN-treated cage-control (ALN-CON, n=13); vehicle-treated plus treadmill running (VEH-RUN, n=13); and ALN-treated plus treadmill running (ALN-RUN, n=13). ALN-treated groups received twice-weekly ALN (0.015 mg/kg), and exercise groups ran on a motorized treadmill at a 5% incline for 60 min/day, 22-24 m/min, 5 days/week. In vivo measurements included dual-energy X-ray absorptiometry (DXA) of whole-body bone mineral content (BMC), and ex vivo measurements included DXA, micro-computed tomography (muCT), and mechanical testing of the femur and L4 vertebrae. After 14 weeks of intervention, exercise and ALN had additive benefits on whole body and proximal femur BMC, cross-sectional area of the L4 vertebrae, and mechanical properties of the mid-shaft femur. In comparison, for total and mid-shaft femur BMC, L4 vertebrae BMC, and mid-shaft femur cortical thickness and area, there were significant exercise and ALN interactions indicating that the two interventions worked in synergy to enhance bone properties. Supporting the contention that ALN and exercise function via distinct mechanisms of action, ALN successfully reduced medullary canal area suggesting it reduced endocortical bone resorption, whereas exercise augmented periosteal perimeter suggesting it stimulated periosteal bone formation. In summary, we found combined treadmill running and ALN to be more beneficial in preventing declines in bone mass and strength following OVX than the introduction of either intervention alone. These data suggest that a comprehensive program of bisphosphonate therapy and weight-bearing exercise may be an effective method for preventing and treating osteoporosis in post-menopausal women.