Effects of Whole Body Exposure to Electromagnetic Field on Normal and Osteoporotic Bone Metabolism in Rats

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1 Effects of Whole Body Exposure to tromagnetic Field on Normal and Osteoporotic Bone Metabolism in Rats S. Fukuda and H. Iida National Institute of Radiological Sciences, Chiba Japan INTRODUCTION The influence of exposure to electromagnetic field induced from our living environment has been argued. For example, it is reported that the electromagnetic wave exposure might increase leukemia in children in the etiology. The safe level is regarded to be less than.mt. On the other hand, the local and short time exposure for the purpose of treatment is suggested rather to accelerate cure of bone fracture. Any way, there are few experimental studies on the effectiveness of electromagnetic wave. The present study is to confirm the effects of electromagnetic wave exposure to rats, particularly on bone metabolism when fed on the diet of different calcium. MATERIALS AND METHODS Animals: Forty Wistar female rats, 8 weeks of age, were divided, as shown in Table 1. Table 1 Groups for the present experiment. Group Standardized diet Low Ca diet No-exposed No-treated (control) Exposed to electromagnetic wave No--treated A half of rats was ovariectomized () and the half was no treated. They were fed on the standardized food (Ca: 1.1 ) or low Ca diet (Ca:.2). The rats of four groups were exposed to electromagnetic wave that produced by an apparatus (Ohtsuka Science Co.): with.1mt (1 mg), Hz for 3 months. During this period, the rats were kept in cages that used no steel. The body weight was measured every week. The rats kept in the room where temperature is 22±2 o C, relative humidity ±, and 12hr light-dark cycle. The food and water were given ad libitum. Bone histomorphometry: Before sacrifices, rats were received twice peritoneal injections of tetracycline at intervals of 7 days for bone double labeling in order to analyze dynamic parameters in bone histomorphometry. Tibia was immersed in Villanueva s bone stain solution, dehydrated in alcohol and embedded in methylmethacrylate. The block was cut thin with cutter (Maruto, Tokyo) and ground to make a thickness of 1 µm with grinding glass. The bone histomorphometric analysis was performed by a semi auto- image analyzer with the soft, Osteoplan II (Car Zeiss) Bone mineral density: The bone mineral density of tibia and femur at the proximal metaphysis (tibia) and distal metaphysis (femur) and of diaphysis of both bones was measured with a peripheral quantitative computed tomography (Stratec and Norland). Bone strength: The breaking force (as an indicator of bone strength) of femur was measured by an apparatus for bone strength measurement (Maruto, Tokyo). The weight of adrenal and skeletal muscles: The weights of adrenal gland and skeletal muscles (soleus) were measured. Serum biochemical analysis: Serum rat-bgp, rat-pth, ALP, GOT, GPT, BUN, creatinine and glucose were measured. RESULTS The suppressions of increase in body weight in the electromagnetic wave-exposed groups were observed compared to no-exposed groups regardless of diet and -treatment (Fig. 1). 1

2 g g Weeks after exposure Weeks after exposure Fig.1 Changes in body weights; left, standardized diet groups, right, low Ca diet groups Total and trabecular bone mineral density of tibia in the exposed groups decreased significantly compared to the no exposed groups, but the trabecular vale in the exposed group fed on standardized calcium diet increased significantly compared to the no exposed group (Fig. 2) Bone strength of femur in the exposed groups decreased significantly compared to the no exposed groups, except for the group of fed on the low Ca diet (Fig. 3). The bone volume (/tissue volume: BV/TV) in all the electromagnetic wave exposed groups decreased compared to the no exposed groups (Fig.4-1). The osteoid volume (/bone volume) tended to increase in the exposed groups except for the groups fed on low Ca diet (Fig. 4-1). mg/cm3 1 7 Total BMD of Tibia mg/cm3 4 3 Trabcular BMD of Tibia Standard Ca Diet Low Ca diet Standard Ca Diet Low Ca diet Fig.2 Bone mineral density of total and trabecular area at the proximal metaphysial tibia. 2

3 Kgf 1 Bone strength of femur 1 Fig.3 Bone strength of femur in each group. 2 Bone volume(bv/tv) 4 Osteoid volume(ob/bv) Standard Ca Diet Fig.4 1 Bone volume (BV/TV) and osteoid volume (OV/BV) in each group. 1 Eroded surface(es/bs) 1 Bone Formation Rate Fig.4-2 Eroded surface (ES/BS) and bone formation rate (BFR/TV) 3

4 mg 4 3 Adrenal gland weight mg 1 1 Muscle(Soleus)weight No-Muscle E-Muscle 2 1 Fig. The weights of adrenal gland and muscle (soleus) in each group The eroded surface (ES/BS) in the exposed groups decreased compared to the n exposed groups, and the bone formation rate in the exposed groups also decreased except for the fed on low Ca diet group (Fig. 4-2). The weights of adrenal gland and skeletal muscle (soleus) in all the exposed groups decreased significantly compared to the no exposed groups (Fig. ) The values of GOT, GPT, ALP, BUN, creatinine and glucose were shown in Table 2. There were seen significant increases in ALP of no groups fed on the standardized diet and groups fed on the low Ca diet, increases in BUN and glucose of no groups fed on the low Ca diet between no electromagnetic wave exposed and no exposed groups. The value of PTH in the exposed no groups fed on the low Ca diet decreased significantly (Table 3). The value of BGP in the exposed groups except for the groups fed on the low Ca diet decreased significantly compared to the no exposed groups (Table 3). Table 2 Serum biochemical values in each group. Group GOT(U/L) GPT(U/L) ALP(U/L) BUN(mg/dl) Creatinine(,g/dl) Glucose(mg/dl) St. diet group No- E+No- 33.6± ± ± ±. 7± 2 87± 7* 2.± ±.7.64±.3.4±.2 134± 9 142± ± ±17. 9± ±1..62±.4 124± 9 E+ 37.± ± ±1 22.4±.6.9±.3 147± Low Ca diet group No- 3.3± ± ±3.±.7.±.3 114± 8 E+No- 28.±.8 9.4±.4 13± ±.6.6±.4 18±1 36.2±. 11.6±.7 133± ±1.6.6±.2 147± 9 E+ 36.6± ±. 21±17* 23.1±.6.9±.1 16± 4

5 Table 3 Serum biochemical values in each group: PTH and BGP Groups PTH(pg/ml) BGP (ng/ml) St. diet group No- E+No- 74.6± ± ± ±1.8* E+ Low Ca diet group No- E+No- 4.8± ± ± ± 7.7* 43.8±. 33.2±2.* 76.6±4. 3.2±1.* E+ 12.6± ±16.8* 69.±3. 73.±4. DISCUSSION Successive exposure of electromagnetic wave retarded the growth of rats, because the weights of body, adrenal gland and muscle in the exposed groups lowered than those in the non-exposed groups, regardless of Ca supplement. The various organs such as kidney, liver and heart might be affected by the electromagnetic wave exposure, because there were not differences in the serum biochemical values between the exposed and noexposed groups. The high mean values of GOT in the No- group given low Ca diet were due to a high value in a rat (Table 2). However, the significant increases in value of alkalinephosphatase activity may be due to any influences in liver (Table 2). Because the value of BGP in the electromagnetic wave exposure groups, an indicator of bone formation, decreased compared to the no-exposed groups, except for the, E--groups given low Ca diet (Table 3). The significant low value of PTH in the electromagnetic wave exposed group given low Ca diet compared to the no-exposed group may indicate that the exposure suppressed the raised bone turnover by and low Ca supplement. In the histomorphometric data, the increase in osteoid volume, the decreases in eroded surface and bone formation rate might also indicate the suppression to the bone turnover, resulting in the decrease in bone volume. Interesting findings were that the bone volumes in the groups received the treatment decreased compared to the corresponding groups, and the magnitude of the decrease enlarged in the groups given low Ca supplement. Such findings were determined in the results of total and trabecular BMD (Fig.2) and might result in the decrease in bone strength (Fig. 3) Also the decrease in the muscle weight might accelerate to decreases in the bone mineral density, volume and strength. The decrease in adrenal gland weight rather appeared the damage than the stress. As a result, the data indicated that a long-term electromagnetic wave exposure to growing rats retarded to bone metabolism as well as the growth. Provided that only the increase in trabecular BMD in the group remains to examine whether the electromagnetic wave exposure, e.g., by locally exposure to bone or other exposure conditions may be useful for osteoporotic bone therapy.