Evaluation of the potential promoting effect of 60 Hz magnetic fields on N-ethyl-N-nitrosourea induced neurogenic tumors in female F344 fats

The present study investigated the possible effect of 60 Hz magnetic fields (MFs) as promoters of neurogenic tumors initiated transplacentally by a ch emical carcinogen, N-ethyl-N-nitrasourea (ENU). In a preliminary study, 5 m g of ENU was shown to induce 30 to 40% neurogenic tumors in F344 rats offsp ring after 420 days of observation. In the present study, 400 female rats w ere divided into eight different groups (50 animals/group) and exposed in u tero ton day 18 of gestation) to a single intravenous dose of either Saline (Group I), or ENU, 5 mg/kg (Group II to VIII). Dams in group II were given no further treatment while dams in Groups III to VII were exposed to 5 dif ferent intensities of MFs forty eight hours later. Animals in group III wer e sham exposed (< 0.02 mu T) while groups IV to VII were exposed to 2, 20, 200 and 2000 mu T, respectively. Dams in Group VIII were injected intraperi toneally with 12-O-tetradecanoylphrobol-13-acetate (TPA; 10 mu g/kg) from d ay 19 until delivery, and then their female offspring continued to be injec ted every 15 days, starting at day 14 after birth until sacrifice (positive controls). Accordingly, this study included three different types of contr ols: Internal controls (Groups II and III and positive control (Group VIII) . Body weight, mortality and clinical observations were evaluated in all gr oups of animals during in-life exposure. Necropsy was performed on all expo sed and central animals that died, were found moribund or sacrificed at ter mination of the study. Histopathological evaluation was done for all brains , spinal cords, cranial nerves, major organs (lungs, liver, spleen, kidneys , pituitary, thyroid and adrenals) and all gross lesions observed during ne cropsy. All clinical observations and pathological evaluations were conduct ed under "blinded" conditions. The findings from this ENU/MFs promotion stu dy clearly demonstrate that, under our defined experimental conditions, exp osure to 60 Hz linear (single axis) sinusoidal, continuous wave MFs had no effect on the survival of female F344 rats or on the number of animals bear ing neurogenic tumors. These results suggest that MFs have no promoting eff ect on neurogenic tumors in the female F344 rats exposed transplacentally t o ENU. (C) 2000,Wiley-Liss, Inc.