EXPOSURE OF DMBA-TREATED FEMALE RATS IN A 50-HZ, 50-MU-TESLA MAGNETIC-FIELD - EFFECTS ON MAMMARY-TUMOR GROWTH, MELATONIN LEVELS, AND T-LYMPHOCYTE ACTIVATION

There is growing public concern about the possible health risks, parti cularly increased cancer risks of exposure to magnetic fields (MF) ass ociated with power distribution systems. Recently, we have started a s eries of animal studies to investigate this issue, using the DMBA (7,1 2-dimethylbenz[a]anthracene) model of breast cancer in female rats, In the present study, female rats were chronically exposed to a 50-Hz, 5 0 mu Tesla (mu T) MF with or without DMBA treatment, Because alteratio ns in circulating levels of the pineal hormone melatonin and impaired immune system functions have been involved in breast cancer growth, an d both melatonin and immune system are thought to be targets for MF-ef fects, serum melatonin and the proliferative capacity of splenic lymph ocytes were determined in MF-exposed and sham-exposed rats, For this p urpose, 216 female Sprague-Dawley rats were divided into four groups, Two of the groups (with 99 animals each) received oral applications of DMBA and were either sham-exposed or exposed in a 50-Hz, 50 mu T MF f or 24 h/day 7 days/week for a period of 91 days, The other two groups (9 animals each) were either sham-exposed or MF-exposed without DMBA t reatment, The exposure chambers and all other environmental factors we re identical for MF-exposed and sham-exposed animals, The DMBA-treated animals were palpated once weekly to assess the development of mammar y tumors, At the end of the three-month period of MF exposure, the num ber and size of mammary tumors was determined by autopsy, In controls, DMBA induced tumors in similar to 55% of the animals within the 3 mon th period of sham-exposure. Already 8 weeks after DMBA application, th e MF-exposed group exhibited significantly more tumors than sham-expos ed animals, At time of autopsy, significantly more MF-exposed DMBA-tre ated rats exhibited macroscopically visible mammary tumors than DMBA-t reated controls, thus indicating that MF exposure enhances the develop ment and growth of cancers in this model, Comparison of the data from 50 mu T with recent data from other flux densities indicated that long -term MF exposure of DMBA-treated rats increases the incidence of palp able and/or macroscopically visible mammary tumors in a highly dose-re lated fashion, Determination of nocturnal serum melatonin after 9 and 12 weeks of exposure at 50 mu T did not yield significant differences between MF-exposed rats and sham-exposed controls, whereas a marked su ppression of T cell proliferative capacity was seen in MF exposed rats , The data add further evidence to the hypothesis that hormone-depende nt tissues such as breast might be particularly sensitive to MF-effect s and indicate that immune system depression is involved in the increa sed breast cancer growth observed in MF exposed rats.