To investigate the effects of electromagnetic fields in combination with different lighting regimes on tumor development in femal rats. Mammary carcinoma (i.e. adenocarcinoma) were induced by intravenously administration of the chemical carcinogen N-nitrosomethylurea (NMU). Furthermore, blood levels of melatonin and prolactin were determined.
Two different experiments were conducted.
Experiment 1) Animals were exposed to three different ligthing regimes (i.e. normal leighting 12 h lightness/12 h darkness; 24 h darkness; or 24 h leightness). After two weeks of acclimatization to the ligthing regims the animals recived the chemical carcinogen NMU in a dose of 50 mg/kg three times at weekly intervals. Magnetic field exposure (either varying or constant) was started from the second day after the first NMU-injection. Animals were exposed for 3 h/day for 15 months. However, blood samples were taken after 4 weeks of MF-exposure to determine melatonin and prolactin levels.
Experiment 2) Animals were kept under a normal light regim (12 h light/12 h dark). A part of the animals were blinded by enucleation of both eyeballs. Two weeks thereafter animals recived a single NMU dose (50 mg/kg). Rats were dissected and histologically examined for tumor classification.
Normal light regime combined with a varying magnetic field leads to a sooner adenocarcinoma development as compared with control groups. However, carcinogenesis was much more stimulated by constant illumination, whereas constant dark inhibited carcinogenesis. Constant illumination leads to an decreased level of melatonin and an increased level of prolactin. Blinded rats exhibited fewer mammary adenocarcinoma and showed an increased expection of life than sighted rats.