摘要:

AbstractSome neurochemical effects of low‐intensity electric and magnetic fields have been shown to be nonlinear functions of exposure parameters. These effects occurred within narrow ranges of frequency and intensity. Previous studies on membrane‐associated endpoints in cell culture preparations demonstrated changes in calcium efflux and in acetylcholinesterase activity following exposure to radiofrequency radiation, amplitude modulated (AM) at 16 and at 60 Hz, at a specific absorption rate of 0.05 W/kg. In this study, these modulation frequencies were tested for their influence on the activity of a cytoplasmic enzyme, enolase, which is being tested clinically for detection of neoplasia.Escherichia colicultures containing a plasmid with a mammalian gene for enolase were exposed for 30 min, and cell extracts were assayed for enolase activity by measuring absorbance at 240 nm. The enolase activity in exposed cultures was compared to the activity in paired control cultures. Exposure to 147 MHz carrier waves at 0.05 W/kg, AM at 16 Hz showed enolase activity enhanced by 62%, and AM at 60 Hz showed enolase activity reduced by 28%. Similarly, exposure to 16 Hz fields alone, at 21.2 V/mrms(electric) and 97 nTrms(magnetic), showed enhancement in enolase activity by 59%, whereas exposure to 60 Hz fields alone, at 14.1 V/mrms(electric) and 65 nTrms(magnetic), showed reduction in activity by 24%. Sham exposures as well as exposure to continuous‐wave 147 MHz radiation at 0.05 W/kg showed no change in enolase activity. Although the underlying basis for these field effects in the cytoplasmic compartment has not been established, differential sensitivities to 16 Hz and to 60 Hz signals provide a clear focus for additional research to determine the responsible mechanism. © 1994 Wiley‐L

ISSN:0197-8462    

DOI:10.1002/bem.2250150502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSeveral reports have shown that weak, extremely‐low‐frequency (ELF), pulsed magnetic fields (PMFs) can adversely affect the early embryonic development of the chick. In this study, freshly fertilized chicken eggs were exposed during the first 48 h of postlaying incubation to PMFs with 100 Hz repetition rate, 1.0 μT peak‐to‐peak amplitude, and 500 μs pulse duration. Two different pulse waveforms were used, having rise and fall times of 85 μs (PMF‐A) or 2.1 μs (PMF‐B). It has been reported that, with 2 day exposure, these fields significantly increase the proportion of developmental abnormalities. In the present study, following exposure, the eggs were allowed to incubate for an additional 9 days in the absence of the PMFs. The embryos were taken out of the eggs and studied blind. Each of the two PMF‐exposed groups showed an excess in the percentage of developmental anomalies compared with the respective sham‐exposed samples. This excess of anomalies was not significant for the PMF‐A‐treated embryos (P= 0.173), whereas it was significant for the PMF‐B‐exposed group (P= 0.007), which showed a particularly high rate of early embryonic death. These results reveal that PMFs can induce irreversible developmental alterations and confirm that the pulse waveform can be a determinant factor in the embryonic response to ELF magnetic fields. The data also validate previous work based on the study of PMFs' effects at day 2 of embryonic development under field expos

ISSN:0197-8462    

DOI:10.1002/bem.2250150503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWe have previously demonstrated that a weak, extremely‐low‐frequency magnetic field must be coherent for some minimum length of time (≈︁ 10 s) in order to affect the specific activity of ornithine decarboxylase (ODC) in L929 mouse cells. In this study we explore whether or not the superposition of an incoherent (noise) magnetic field can block the bioeffect of a coherent 60 Hz magnetic field, since the sum of the two fields is incoherent. An experimental test of this idea was conducted using as a biological marker the twofold enhancement of ODC activity found in L929 murine cells after exposure to a 60 Hz, 10 μTrmsmagnetic field. We superimposed an incoherent magnetic noise field, containing frequencies from 30 to 90 Hz, whose rms amplitude was comparable to that of the 60 Hz field. Under these conditions the ODC activity observed after exposure was equal to control levels. It is concluded that the superposition of incoherent magnetic fields can block the enhancement of ODC activity by a coherent magnetic field if the strength of the incoherent field is equal to or greater than that of the coherent field. When the superimposed, incoherent noise field was reduced in strength, the enhancement of ODC activity by the coherent field increased. Full ODC enhancement was obtained when the rms value of the applied EM noise was less than one‐tenth that of the coherent field. These results are discussed in relation to the question of cellular detection of weak EM fields in the presence of endogenous thermal noise fields. © 1994 Wile

ISSN:0197-8462    

DOI:10.1002/bem.2250150504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWork in our laboratory has revealed autonomic and/or behavioral sensitivity of mice, rats, and a domestic fowl to extremely‐low‐frequency (ELF) or nominally static magnetic (B) fields at flux densities between 250 and 1700 μT (rms). To extend our work, an automated exposure and data‐acquisition system was used with the technique of conditional suppression to assess behavioral sensitivity to time‐varying B fields. Each of five rats was exposed aperiodically to a B field during 3 min warning periods that terminated in a brief electric shock. The difference between rates of lever pressing during B‐field warning periods and rates during immediately antecedent, 3 min control periods was analyzed at frequencies of 7, 16, 30, 60, and 65.1 Hz. To produce equivalent induced voltages in the rat at each frequency, graded flux densities were established that ranged from 1900 μT at 7 Hz to 200 μT at 65.1 Hz. Analysis of differences in lever‐pressing rates revealed that in a given session of testing the rats would increasingly suppress responding when exposed to a B field, but this trend was independent of frequency. This experiment provides evidence of behavioral sensitivity by a mammal to an ELF magnetic field. © 1994

ISSN:0197-8462    

DOI:10.1002/bem.2250150505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSprague‐Dawley male rats, maintained in a 14:10 h light:dark cycl were exposed for 30 days (starting at 56 days of age) to a 65 kV/m, 60 Hz electric field or to a sham field for 20 h/day beginning at dark onset. Pineal N‐acetyltransferase (NAT), hydroxy‐indole‐o‐methyl transferase (HIOMT), and melatonin as well as serum melatonin were assayed. Preliminary data on unexposed animals indicated that samples obtained 4 h into the dark period would reveal either a phase delay or depression in circadian melatonin synthesis and secretion. Exposure to electric fields for 30 days did not alter the expected nighttime increase in pineal NAT, HIOMT, or melatonin. Serum melatonin levels were also increased at night, but the electric field‐exposed animals had lower levels than the sham‐exposed animals. Concurrent exposure to red light and the electric field or exposure to the electric field at a different time of the day‐night period did not reduce melatonin synthesis. These data do not support the hypothesis that chronic electric field exposure reduces pineal melatonin synthesis in young adult male rats. However, serum melatonin levels were reduced by electric field exposure, suggesting the possibility that degradation or tissue uptake of melatonin is stimulated by exposure to electric fields. © 1994

ISSN:0197-8462    

DOI:10.1002/bem.2250150506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFlux density and spectral measurements were carried out on magnetic fields generated by several types of motor‐driven personal appliances used near the body. Among the units tested were several for which the average flux densities, as determined at the surfaces of the appliance, exceeded 0.4 mT. Time‐rates‐of‐change (dB/dt) for several units exceeded 1000 T/s, and several units exhibited high‐frequency components in the low‐MHz range. Use of such appliances, although normally of short duration, can represent exposure to magnetic fields of relatively high flux density, which may also have high‐frequency components. Compared to other household and commercial sources of magnetic fields, those generated by certain motor‐driven personal appliances may represent a significant contribution to time‐weighted average exposure and may represent an important source of local induced currents in the body. Furthermore, high‐frequency transients that represent only a minor contribution to time‐weighted average exposure may generate significant instantaneous induced currents. © 1994 Wiley‐Liss, Inc.This article is a US Government work and, as such, is in the public domain in the

ISSN:0197-8462    

DOI:10.1002/bem.2250150507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis human exposure study examined the relationship between field strength and biological response and tested whether the exposure levels at which the greatest effects occur differ for different endpoints. Three matched groups of 18 men each participated in two 6 h exposure test sessions. All subjects were sham exposed in one session. In the other session, each group of subjects was exposed at a different level of combined electric and magnetic field strength (low group: 6 kV/m, 10 μT; medium group: 9 kV/m, 20 μT; and high group: 12 kV/m, 30 μT). The study was performed double blind, with exposure order counterbalanced. Significant slowing of heart rate, as well as alterations in the latency and amplitude of event‐related brain potential measures derived from the electro encephalogram (EEG), occurred in the group exposed to the 9 kV/m, 20 μT combined field (medium group). Exposure at the other field strength levels had no influence on cardiac measures and differential effects on EEG activity. Significant decrements in reaction time and in performance accuracy on a time estimation task were observed only in the low group. These results provide support for the hypothesis that humans may be more responsive to some combinations or levels of field strength than to others and that such differences in responsivity may depend, in part, on the endpoint of interest. © 1994 Wiley‐L

ISSN:0197-8462    

DOI:10.1002/bem.2250150508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA commercially available spreadsheet program is used on a microcomputer to calculate the induced current density and electric field patterns produced in a nonhomogeneous, anisotropic model of tissue by a localized, low‐frequency magnetic field source. Specific application is made to coils used to promote the healing of bone fractures in limbs. The variation of the conductivity of the fracture gap during healing causes the induced current density pattern to change correspondingly, whereas the induced electric field remains relatively unchanged. Use of more simplified, isotropic models for the bone and for the soft tissue leads to results that differ significantly from those obtained from the full model. The magnetic field beyond the region of the coils contributes little to the induced currents in the fracture gap if the gap is located near the center of the coils. © 1994 Wiley‐Liss,

ISSN:0197-8462    

DOI:10.1002/bem.2250150509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractMeasuring internal induced electric fields in animals with a miniaturized probe involves a potential error related to the difference between the hole conductivity (σh) and the surrounding tissue conductivity (σt). Theory was developed to describe this phenomenon and checked by probe measurements in agar‐filled petri dishes. The value measured in the hole is 2σt/(σh+ σt) times the actual field in the tissue. For example, a probe hole in muscle, which is filled with blood, could yield a measurement only about 22% of the true value in the muscle. This potential source of error can be mitigated to some extent by not actually cutting a hole, by using a low‐conductivity (e.g., 0.2 S/m) coupling medium in the hole, or by ensuring contact between the probe's electrodes and the tissue. © 1994 Wiley

ISSN:0197-8462    

DOI:10.1002/bem.2250150510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn our earlier paper [Kato et al. (1993): Bioelectromagnetics 14:97–106], melatonin concentration in pineal gland and blood was reported to be suppressed after exposure to a circularly polarized 50 Hz magnetic field for 6 weeks. In the present series of experiments, we investigated the time course of recovery after cessation of the exposure. Rats were exposed to a circularly polarized 50 Hz magnetic field at 1 μT for 6 weeks, and the melatonin concentration of blood of separate groups was determined at the end of the exposure and at 1 week and 4 weeks following cessation of exposure. Nocturnal melatonin concentration was reduced (P<0.05) after 6 weeks of exposure. Melatonin concentration at 1 week following cessation of exposure was normal, and no further change was observed 4 weeks later. © 1994 Wiley‐Liss

ISSN:0197-8462    

DOI:10.1002/bem.2250150511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY