An intensity window in the effects of pulsed electromagnetic fields on bone metabolism in ovariectomized rats

Objective To investigate the effects of pulsed electromagnetic fields (PEMFs) of different intensities on bone metabolism in ovariectomized rata. Methods Sixty 10-month-old female Sprague-Dawley rats were randomly divided into a normal group, an ovariectomized control group, a 0. 14 mT group, a 0. 16 mT group, a 0.18 mT group and an estrogen group. All rats except those in the normal group were subjected to bilateral ovariectomy. Beginning one week after the operation, the rats in the 0. 14 mT, 0. 16 mT and 0.18 mT groups were treated with PEMFs at 50 Hz, 60 min daily for 90 days, while those in the estrogen group received estrogen instead. During the experiment, the bone mineral density (BMD) of the whole body was observed dynamically, and local BMDs and biochemical indexes were measured after 3 months of treatment. Results Alkaline phosphatase (ALP) activity in the normal group was significantly lower than in the other groups. Tartrate-resistant acidic phosphatase 5b (TRAP5b)activity was elevated significantly, in the control and 0.14 mT groups compared with the normal group. After 2 months of treatment, whole body BMD was reduced significantly in the 0.14 mT group compared to the normal group. After 3 months of treatment, whole body BMD in the ovariectomized controls and the 0.14 mT group was reduced significantly compared to the normal group, but significantly elevated in the 0. 16 mT, 0.18 mT and estrogen groups when compared to the ovariectomized control group. At the end of 3 months of treatment, the trends in lumbar vertebral BMD were similar to those of the whole body BMD, with the femoral BMD in the ovariectomized group and the 0.14 mT group significantly lower than in the normal group, though the differences among the other groups were not statistically significant. Conclusions PEMF treatment at 50 Hz and 0.16 mT or 0.18 mT can promote bone formation. PEMFs at 50 Hz and 0.14 mT might stimulate bone resorption. An intensity-window effect exists in the action of PEMFs on bone metabolism in ovariectomized rats. Key words: Pulsed electromagnetic fields; Ovariectomies; Bone metabolism; Intensity