In vivo exposure of rats to a weak alternating magnetic field increases ornithine decarboxylase activity in the mammary gland by a similar extent as the carcinogen DMBA.

Magnetic field (MF) exposure has been discussed in the process of tumor promotion as indicated by epidemiologic data as well as laboratory studies. However, the precise mechanisms of tumor promoting effects of MFs are unknown. Tumor promotion is often accompanied by an increase in the activity of the enzyme ornithine decarboxylase (ODC), i.e. a key enzyme in the biosynthesis of polyamines, which have roles in cell proliferation and control of gene expression. In the present work, we studied if exposure of female rats to a 50-Hz MF with a flux density of 50 microT influences ODC activity in different tissues, including the mamma. Rats were exposed for a period of 6 weeks either with or without oral administration of the chemical carcinogen DMBA and all data were compared with those from sham-exposed controls. Magnetic field exposure resulted in an approximate doubling of ODC in mammary tissue. A significant ODC increase was also seen in the spleen, but not in the liver, small intestine, bone marrow, and ear skin. The ODC increase produced by MF exposure in the mammae was of similar magnitude as that observed after treatment with DMBA. Combined treatment with MF and DMBA was not more effective in increasing ODC than treatment with DMBA alone, except for liver tissue. The present results on in vivo increases of ODC by MF exposure strengthen the hypothesis that weak 50-Hz MFs affect ODC activity and may thus function as a tumor-promoting or co-promoting agent.