MAMMARY-TUMORS IN SPRAGUE-DAWLEY RATS AFTER INITIATION WITH DMBA FOLLOWED BY EXPOSURE TO 50 HZ ELECTROMAGNETIC-FIELDS IN A PROMOTIONAL SCHEME

In order to test whether a transient-producing intermittent magnetic f ield (MF) acts as a promoter in rat mammary tumour development, a stud y of a 50 Hz sinusoidal MF with flux densities of 0.25 and 0.5 mT was performed on female Sprague-Dawley rats. A single administration of 7 mg of 7,12-dimethyl-benz[a]anthracene (DMBA) was given by gavage to 52 -day-old animals, After 1 week, exposure to an intermittent (15 s on/1 5 s off) transient-associated magnetic field was started. MF exposure was performed for 19 or 21 h per day up to 25 weeks, when the study wa s terminated. Twice a week a careful examination with palpation for tu mours was done. Tumour incidence, the number of tumours per animal, tu mour volume and tumour weight were recorded. A total of 70% of MF-expo sed animals developed tumours. For animals exposed to DMBA alone the c orrespondent figure was 71.7%. No statistical differences were seen ei ther for tumour-bearing animals or for the total number of tumours. A slightly larger total tumour weight and tumour volume was seen for ani mals exposed to 0.25 mT MF. These differences were not statistically s ignificant. (C) 1998 Elsevier Science Ireland Ltd.