Effects of Weak Alternating Magnetic Fields on Nocturnal Melatonin Production and Mammary Carcinogenesis in Rats

Abstract

Since extremely low frequency (i.e., 50- or 60-Hz) magnetic fields (MFs) from overhead power lines and other electromagnetic sources are ubiquitous in modern societies, the possible carcinogenic effect of such fields recently suggested by epidemiological studies has engendered much concern. However, in view of various unknown and uncontrolled variables which may bias epidemiological studies on MF interactions, a causal relationship between MFs and tumorigenesis can only be determined precisely in animal experiments. The goal of the study reported here was to determine if low frequency MFs at the low flux densities which are relevant for human populations induce tumor-promoting or copromoting effects in a model of breast cancer. Furthermore, since reduction in pineal production of melatonin has been implicated as a cause of tumor promotion by electromagnetic fields, determinations of nocturnal melatonin peak levels in serum were performed during MF exposure. Mammary tumors were induced by intragastric administration of 20 mg (5 mg/week) 7,12-dimethylbenz(a)anthracene (DMBA) in female Sprague-Dawley rats. Groups of 36 rats were either sham-exposed or exposed for 91 days at a 50-Hz gradient MF of 0.3-1 µT, which is a relevant range for elevated domestic MF exposure as arising from neighboring power lines. Nocturnal melatonin levels were significantly reduced by exposure to this weak alternating MF. However, histopathological evaluation of mammary lesions did not disclose any significant difference between MF- and sham-exposed animals. Incidence of mammary tumors was 61% in controls versus 67% in MF-exposed rats. The predominant tumor type was the invasive adenocarcinoma, which was found in 21 rats of both groups. Examination of tumor size did not indicate significant differences in tumor burden between both groups. Furthermore, the incidence of preneoplastic lesions was not altered by MF exposure. Thus, the data of this study indicate that alternating MF do not exert signficant tumor promoting or copromoting effects at environmentally relevant flux densities in the rat mammary cancer system.

The Melatonin Hypothesis: Electric Power and Breast Cancer

“…No tumors developed in 50 control rats over the 2-year study period, whereas seven tumors appeared in 25 rats exposed to the 50-Hz magnetic field for 3 hr/day. The results of Beniashvili et al (43) (30,(45)(46)(47)(48).…”

“…Since the Semm et al (21) (24)(25)(26)(27), and AC magnetic fields (28)(29)(30). There have also been reports that such fields have little or no effect (31)(32)(33).…”

“…There have also been reports that such fields have little or no effect (31)(32)(33). AC magnetic fields as low as 10 mG have been reported to suppress melatonin in rats (29,30). The differences among experimental reports may result from real differences in the effectiveness of the fields employed in each experiment, from artifacts associated with the EMF exposures, such as noise or other stress that account for a reduction of melatonin production in those experiments claiming to show effects of EMF; or from real effects on melatonin that are sometimes masked by natural biological variability.…”

Testing Electromagnetic Fields for Potential Carcinogenic Activity: A Critical Review of Animal Models

“…As shown in Table 4, results of two experiments at the 0.3 to 1.0 pT flux density have been reported (34,40,41). In each experiment, a group of 36 rats was exposed to the gradient ac sine wave 50-Hz field and a group of 36 was exposed to a sham field.…”

“…Most work with this system is from Loscher and his colleagues (34,(40)(41)(42)(43)(44)(45)(46). In all experiments, female Sprague-Dawley rats 6 to 8 weeks of age were exposed by gavage to DMBA (four weekly doses at 5 mg/rat/dose) beginning on the first day of MF exposure.…”