Pituitary Toxicity but Lack of Rat Colon Carcinogenicity of a DC-Magnetic Field in a Medium-Term Bioassay

The present study was designated to evaluate the effect of direct current induced permanent magnetic field(DC-MF) on chemically induced rat colon carcinogenesis. Five experimental groups of male S.D. rats wereinjected with 1,2-dimethylhydrazine (DMH) subcutaneously, 20 mg/kg b.wt., once a week for four weeks, withexposure to 1 mT DC-MF (12 hours/day) as follows: Before (pre) the carcinogen administration (group 1),simultaneously (group 2), after (post) the carcinogen administration (group 3) and daily from the beginning tothe end of the experiment after 12 weeks (group 4). Rats of group 5 served as carcinogen-only treated controlswhile those of group 6 were non-treated controls. There were no differences in the incidences and multiplicitiesof colonic aberrant crypt foci (ACF), putative preneoplastic lesions, among all groups except that large foci ingroup 1 were significantly fewer in numbers than those found in group 5. Proliferating cell nuclear antigenlabeling indexes (PCNA-LI) in the colon epithelium were essentially the same in MF-treated and control rats.Histopathological examination showed evident hemorrhage in the pituitary glands of some rats of groups 1-3,and in most rats of group 4. Transmission electron microscopy also revealed ultrastructural changes, but DNAploidy analysis revealed no carcinogenicity to MF-exposed pituitary glands. Serum levels of AST, ALT, totalprotein, creatinine, albumin, albumin/globulin ratio and growth hormone levels did not change among thegroups. The present study revealed that the action of an artificial MF on rats is not carcinogenic/or cancerpromoting,at least in the present protocol for colon carcinogenesis.