Skip to main content

Currently Skimming:

4 Animal and Tissue Effects
Pages 73-116

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 73...
... To date, no reports have been published showing demonstrable effects of electric- or magnetic-field exposures on the incidence of various types of cancer. However, some recent, as yet unreplicated laboratory evidence suggests a positive relationship between magnetic-field exposures at field strengths of approximately 100 AT (1 G)
From page 74...
... . The data supporting an effect of sinusoidal electric fields on melatonin production are not compelling.
From page 75...
... Early in an investigation of the toxicity of an agent, the best end point for effects might not be apparent, but as more is known about the manifestations of toxicity, the dose-response relationship should become more quantifiable. These assumptions hold true for all types of toxic agents, presumably including extremely-low-frequency electric and magnetic fields, if such fields are found .
From page 76...
... In animal studies on the effects of exposure to electric and magnetic fields, acute toxicity studies involve effects from high-strength current flows. The physical effects and behavioral changes present in animals receiving perceptible electric shocks do not seem appropriate for the exposure conditions under which most people are exposed to electric and magnetic fields.
From page 77...
... No subchronic toxicity studies using electric and magnetic fields have been conducted that meet the criteria necessary for defining subchronic toxicity. This deficiency is primarily due to the lack of repeatable toxic effects and the lack of a definition of doseresponse relationships required from repeated-dose studies to establish dosages for a successful subchronic toxicity study.
From page 78...
... To conduct reproductive and developmental studies properly, concentrations must be known that do not result in overt adverse effects in males and females; overt toxicity is widely known to have severe effects on reproduction and development in males and females. Thus, in the absence of good dose-response information from acute toxicity, repeated-dose, and subchronic toxicity studies, informative reproductive and developmental toxicity studies are nearly impossible to conduct.
From page 79...
... Thus, the positive results in such tests are questionable until detailed studies have identified the underlying mechanism and the probable interaction of doses at environmental concentrations. Nevertheless, electric and magnetic fields, principally magnetic fields, have been shown to interact with carcinogens in some of these systems both in vitro and in vivo, and that fact raises some concern and deserves further attention.
From page 80...
... Interpretation of such studies is for identification of possible toxic mechanisms, not for direct extrapolation to human risk. Complete Carcinogen Studies Few life-long animal studies examining power-frequency electric or magnetic fields as a complete carcinogen have been completed, although several are under way in the United States, Italy, Japan, and Canada.
From page 81...
... (1991) study found an increase in mammary gland tumors in rats exposed to magnetic fields at 20 AT for 3 hr per day as compared with unexposed animals.
From page 82...
... It is divided into considerations of effects of electric fields and magnetic fields. This division is somewhat artificial because all time-varying electric fields have an associated magnetic field; however, at these low frequencies, the fields can be considered independently to a high degree of accuracy.
From page 83...
... was unable to identify an exposure-related change in mortality of the progeny of mice exposed to 60-Hz electric fields at 240 kV/m. In this study, mice were exposed throughout gestation, the offspring were bred, and their litters were monitored for growth, blood histologic and biochemical changes, and histologic changes of major organs.
From page 84...
... were unable to detect any exposure-related effects in the offspring of male rats exposed to 50-Hz electric fields at 100 kV/m. Male rats were exposed for 30 min per day or 8 hr per day for up to 48 days.
From page 85...
... (1984) were unable to detect any exposure-related effects on the perinatal development of rats exposed to 60-Hz electric fields at 65 kV/m (effective field strength)
From page 86...
... (1990) found in vitro effects of electric fields in embryos of rats and mice, but they were unable to detect effects in fetuses exposed in vivo.
From page 87...
... Cattle Algers and Hultgren (1987) exposed pregnant cattle to 50-Hz electric fields at 4 kV/m and magnetic fields at 2.0 AT (20 mG)
From page 88...
... Mice were exposed to a magnetic field with amplitude varying in a saw-tooth shape with a repetition rate of 20 kHz and field strengths of 3.6, 17, or 200 AT from day 1 to day 19 of pregnancy. This study was unusual in that large numbers of animals were used (185 controls and three groups of 186 pregnant females)
From page 89...
... (1990) exposed rats to a 15-Hz pulsed magnetic field of 0.3-msec duration, 330-msec rise time, and peak strength of 800 AT.
From page 90...
... This section is divided into discussions of studies using electric fields and those using magnetic fields or combined electric and magnetic fields. Simple and complex responses are also discussed separately.
From page 91...
... Magnetic Fields Although signal detection methods have provided evidence of the ability of mammals to detect electric fields, such evidence is not available for magnetic fields except at very high field strengths (i.e., magnetic excitation of endogenous phosphenes)
From page 92...
... (1990) reported results from rats exposed perinatally to 60-Hz electric fields at 30 kV/m and 100-~T magnetic fields for 22 days in utero and for 20 hr per day during the first 8 days postpartum.
From page 93...
... They suggested that the lack of aversion in these magneticfield experiments indicates that aversive behavior produced by electric fields might be associated with body-surface interactions rather than internal-body currents resulting from electric-field exposure. Summary of Neurobehavioral Effects Mammals clearly can detect 60-Hz electric fields at relatively modest field strengths (above a few kilovolts per meter)
From page 94...
... Hypothalamic and striatal norepinephrine, serotonin, dopamine, and 5-hydroxyindole acetic acid, as well as the dopamine metabolite dihydroxyphenyl acetic acid were measured following the exposure of rats to an electric field for 20 hr per day for 30 days; the measurements were made at six time points (three during the night and three during the day) throughout a 24-hr period.
From page 95...
... Following exposure of the rats to electric fields for 14 days, a generalized increase in striatal concentrations of all the neurotransmitters was observed. On the other hand, after 56 days of exposure, the concentrations of these neurotransmitters in the striatum were depressed.
From page 96...
... Thus, the mechanisms of physical interactions of these different wavelengths might vary radically. Elects of Electric Fields on Animals The peer-reviewed reports that investigated the effects of sinusoidal electric fields on pineal serotonin metabolism and melatonin production and secretion are summarized in Table A4-7.
From page 97...
... In the first experiment, a reduced concentration of melatonin was observed 6 hr after onset of darkness in rats that had been exposed to 60-Hz electric fields for 1 month; however, a change in the 5-methoxytryptophol concentration after exposure was not significant. In the second experiment using comparable exposure conditions, pineal melatonin concentrations and NAT activity were estimated.
From page 98...
... After an exposure regimen of 30 days, neither daytime or nighttime pineal NAT activity, pineal HIOMT activity, nor pineal melatonin concentrations differed between the exposed and the sham-exposed animals. Serum melatonin concentrations were reported to be significantly
From page 99...
... How or whether these changes are significant in terms of pineal-gland function remains unknown. An extensive number of earlier reports illustrated the suppressive effects of pulsed or perturbed static magnetic fields on pineal melatonin production (Olcese and Reuss 1986; Wilson et al.
From page 100...
... (1993) report is the modest rise in daytime pineal melatonin concentrations in one study in which rats were exposed to field strengths of either 1, 5, or 50 AT.
From page 101...
... In successive studies performed during various seasons over several years, Yellon claimed that brief daytime exposures to unusual magnetic-field environments alter the underlying biologic clock mechanisms of the organism, thereby changing nocturnal melatonin synthesis by the pineal gland. In these studies, male and female Djungarian hamsters were exposed to a 60-Hz horizontal magnetic field at 100 AT (1 G)
From page 102...
... Although no significant alterations in blood melatonin concentrations were noted, interpretation of the data is confounded by the observation of Schiffman et al.
From page 103...
... These authors exposed groups of mice to a 60-Hz electric field at a field strength of either 25 or SO kV/m. The onset of the fields was associated with a transient and low-amplitude rise in circulating corticosterone concentrations; that short-term peak lasted less than 15 min.
From page 104...
... were not changed by either continuous or intermittent electric-field exposure. The final study on the neuroendocrine physiology of animals exposed to electric fields was published by Portet and Cabanes (19883.
From page 105...
... Consistency and Plausibility of Results Surprisingly few studies have examined the potential neurochemical changes associated with the exposure of animals to very-low-frequency sinusoidal electric or magnetic fields. In fact, despite the current widespread interest in the biologic consequences of time-varying magnetic fields in this area of neurobiology (exclusive of those on the pineal gland)
From page 106...
... Another reason for the interest in the reported melatonin changes is their potential relationship to the higher incidence of cancer reported in some epidemiologic studies. Two biologically plausible, although unproved, mechanisms theoretically describe a link between reduced melatonin concentrations and cancer initiation, promotion, and progression (Figure 4-24.
From page 107...
... T Need for total antioxidative antioxidative capacity of capacity organism t Likelihood of oxidative damage by carcinogens Likelihood of a wide variety of tumors FIGURE 4-2 The two theories that have been proposed to explain the potential association of reduced melatonin production with the alleged increase in cancer after exposure to electric and magnetic fields. On the left, reduced melatonin concentrations lead to an increased secretion of prolactin and gonadal steroids.
From page 108...
... 1994~. Little evidence can be found for effects of magnetic or electric fields on bone at magnetic-field strengths below 100 AT (1 G)
From page 109...
... The mineral component of bone (hydroxyapatiteJ apparently contributes to the piezoelectric process mainly as an insulator that limits dispersion of charges produced by compaction of collagen fibers (Pollack 19841. Another postulated source of endogenous electric fields in bone is the electric processes of living bone cells, which contribute significantly to the higher current densities detected in living bone as opposed to dead bone (Friedenberg et al.
From page 110...
... Locally generated electric phenomena in normal bone remodeling and fracture healing are believed by many researchers to be involved in a process in which areas of bone that accumulate negative charge are subject to increased deposition of bone matrix, and areas of positive charge are subject to increased resorption of existing bone matrix (Dealler 1981~. That hypothesis is based on observations that, during chronic flexure of living bone, the areas of bone undergoing compression are the sites of increased bone formation ("Wolff's law"; Wolff 1892)
From page 111...
... No evidence of increases in cancer or other diseases has been found despite the high field strengths used in comparison with environmental field strengths (Compere 1982; Bassett 1989~. A small number of other clinical devices are also approved for use in stimulating bone healing.
From page 112...
... Potential Mechanisms of Electric- and l\lagnetic-Field Effects on Bone The mechanistic bases have not been clearly established for the effects of either do or pulsed electric fields on bone healing. Most evidence suggests that changes in osteoblast activities are the major functions responsible for bone responses to electric- and magnetic-field exposure (Watson and Downes 1979; Dealler 1981; Friedenberg and Brighton 1981; Bassett 1983~.
From page 113...
... McLeod and colleagues used a number of in vivo and in vitro systems to study the biophysical and cellular biologic properties of bone exposed to electric and magnetic fields. They showed that electric fields induced by devices promoting bone healing are the most likely operative influence on bone-cell function (Rubin et al.
From page 114...
... (1989) , who showed that pulsed electric fields increased DNA synthesis in rapidly growing bone cells but not in bone cells that had already reached a contact-inhibited more-differentiated status.
From page 115...
... 1982~. There are some potential clues to the possible molecular mechanism of PTH receptor desensitization by electric and magnetic fields.
From page 116...
... In the very few tumorpromotion studies that have been reported, results seem to be mixed; most studies show no association between exposure to electric and magnetic fields and increased tumor development. Although the data are not strong or entirely consistent, some experimental results using animal cancer models suggest a possible association of exposure to electric arid magnetic fields and adverse health outcomes.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.