Recovery Effects of a 180 mT Static Magnetic Field on Bone Mineral Density of Osteoporotic Lumbar Vertebrae in Ovariectomized Rats

Abstract

The effects of a moderate-intensity static magnetic field (SMF) on osteoporosis of the lumbar vertebrae were studied in ovariectomized rats. A small disc magnet (maximum magnetic flux density 180 mT) was implanted to the right side of spinous process of the third lumbar vertebra. Female rats in the growth stage (10 weeks old) were randomly divided into 4 groups: (i) ovariectomized and implanted with a disc magnet (SMF); (ii) ovariectomized and implanted with a nonmagnetized disc (sham); (iii) ovariectomized alone (OVX) and (vi) intact, nonoperated cage control (CTL). The blood serum 17-β-estradiol (E(2)) concentrations were measured by radioimmunoassay, and the bone mineral density (BMD) values of the femurs and the lumbar vertebrae were assessed by dual energy X-ray absorptiometry. The E(2) concentrations were statistically significantly lower for all three operated groups than those of the CTL group at the 6th week. Although there was no statistical significant difference in the E(2) concentrations between the SMF-exposed and sham-exposed groups, the BMD values of the lumbar vertebrae proximal to the SMF-exposed area statistically significantly increased in the SMF-exposed group than in the sham-exposed group. These results suggest that the SMF increased the BMD values of osteoporotic lumbar vertebrae in the ovariectomized rats.

Figure 1

(a) Spatial distribution of the magnetic flux density values. (b) Spatial distribution of the magnetic gradient values.

Figure 2

A magnet was implanted to the right side of spinous process of the third lumbar vertebra (L₃). (a) Spatial distribution of the magnetic flux density values in lumbar vertebrae (unit: mT). Arrows show the direction of DXA beam under measurement after removal of the magnet. Encircled number indicates each lumbar vertebra. (b) Spatial distribution of the magnetic flux density values in a lumbar vertebra L₃ (unit: mT). N: north-seeking side; S: south-seeking side.

Figure 3

The rat body weight changes after ovariectomy or nonovariectomy. SMF: ovariectomized and implanted with a disc magnet; Sham: ovariectomized and implanted with a nonmagnetized disc; OVX: ovariectomized alone; CTL: intact (nonoperated) cage control. n = 10 in each group. **P < .01 versus CTL.

Figure 4

The E₂ concentrations in the rat blood serum 6 weeks after ovariectomy or nonovariectomy. SMF: ovariectomized and implanted with a disc magnet; Sham: ovariectomized and implanted with a nonmagnetized disc; OVX: ovariectomized alone; CTL: intact (nonoperated) cage control. n = 10 in each group. *P < .05 versus CTL. no. of rats under the detection limit (<5 pg/mL): SMF, n = 7; Sham, n = 7; OVX, n = 3; CTL, n = 2. These E₂ levels were shown as “0” at the E₂ concentration.

Figure 5

The BMD values of the rat femurs 6 weeks after ovariectomy or nonovariectomy. SMF: ovariectomized and implanted with a disc magnet; Sham: ovariectomized and implanted with a nonmagnetized disc; OVX: ovariectomized alone; CTL: intact (nonoperated) cage control. n = 20 in each group. *P < .05; **P < .01; ***P < .001 versus CTL.

Figure 6

The BMD values of the rat lumbar vertebrae L₂, L₃, and L₄ 6 weeks after ovariectomy or nonovariectomy. SMF: ovariectomized and implanted with a disc magnet; Sham: ovariectomized and implanted with a nonmagnetized disc; OVX: ovariectomized alone; CTL: intact (nonoperated) cage control. n = 10 in each group. *P < .05; **P < .01; ***P < .001 versus sham or CTL.

Figure 7

A hypothetical relationship diagram between SMF and hemodynamics that explains the possible mechanisms. Abbreviations: AChE: acetylcholinesterase; Ach: acetylcholine; NOS: nitric oxide synthase; NO: nitric oxide.