Mated Wistar rats were chronically exposed to a static magnetic field (MF) from day 1 to day 20 of pregnancy. Flux density of the MF was 30 mTesla (mT), i.e., within the range of exposures of operators of magnetic resonance imaging (MRI) devices. For comparison with effects of this static field, a time-varying (50-Hz) MF of the same flux density was used. In both experiments, i.e., static or 50-Hz MF exposure, sham-exposed groups of dams served as controls. On day 20, the dams were sacrificed for reproductive and teratological assessment. The litters were evaluated for numbers of implantations, fetal deaths and resorptions, gross external, visceral, and skeletal malformations, and fetal weights. No adverse effects were seen in the dams during MF exposure. The mean number of living fetuses per litter was significantly decreased in the group with static MF exposure, but not the group with 50-Hz MF exposure. Further differences between the two types of field exposure were observed with respect to minor (skeletal) fetal anomalies which were increased in the 50-Hz but not the static MF group. No serious malformations were seen in any group. In both MF-exposed groups, increased skeletal ossification was found, possibly indicating an accelerated prenatal development. In a second experiment with static MF (30 mT) in which dams were exposed for the whole period of pregnancy, and postnatal growth and development of offspring were studied, the postnatal growth was significantly enhanced in offspring following their prenatal MF exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

A series of epidemiological studies have indicated associations between exposure to magnetic fields (MFs) and a variety of cancers, including breast cancer. In order to test the possibility that MF acts as a cancer promoter or copromoter, four separate experiments have been conducted in rats in which the effects of chronic exposure to MFs on the development of mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) were determined. Female rats were exposed in magnetic coils for 91 days (24 h/day) to either alternating current (AC; 50 Hz)-MF or direct current (DC)-MF. Magnetic flux density of the DC-MF was 15 mT. Two AC-MF exposures used a homogeneous field with a flux density of 30 mT (rms); one used a gradient field with flux density ranging from 0.3-1 microT. DMBA (5 mg) was administered orally at the onset of MF exposure and was repeated thrice at intervals of 1 week. In each experiment, 18-36 animals were exposed in 6 magnetic coils. The same number of rats were used as sham-exposed control. These control animals were treated with DMBA and were placed in dummy coils in the same room as the MF-exposed rats. Furthermore, groups of age-matched rats (reference controls) were treated with DMBA but housed in another room to exclude any MF exposure due to the magnetic stray field from the MF produced by coils. At the end of the exposure or sham-exposure period, tumor number and weight or size of tumors were determined at necropsy. Results were as follows: In sham-exposed animals or reference controls, the tumor incidence varied between 50 and 78% in the 4 experiments. The average number of mammary tumors per tumor-bearing animal varied between 1.6 and 2.9. In none of the experiments did MFs significantly alter tumor incidence, but in one of the experiments with AC-MF exposure at 30 mT, the number of tumors per tumor-bearing animal was significantly increased. Furthermore, exposure to a DC-MF at 15 mT significantly enhanced the tumor weight. Exposure to a gradient AC-MF at 0.3-1 microT exerted no significant effects. These experiments seem to indicate that MFs at high flux densities may act as a promoter or copromoter of breast cancer. However, this interpretation must be considered only a tentative conclusion because of the limitations of this study, particularly the small sample size used for MF exposure and the lack of repetition of data.

Detweiler, D. K. ( 1952). 89, 120-129. Equine Vet. J . 3, 110-1 13. 57-72. the treatment of atrial fibrillation in 12 horses. 95 1-960. Adv. Anini. ECG No. 7, 44-50. Kroneman, J. and Breukink, H. J. (1966). Wien. Tierarztl. Mschr. 21, 689-692. 107, 435-456. ABSTRACT Parasitology Onchocerca cervicalis Infection in Horses from the Western United States STANNARD, A. A. and CELLO, R. M. (1975).The authors describe the results of an investigation o n the prevalence of Onchocerca cervicalis infection and the distribution concentration and pathogenicity of microfilariae in the skin. On examination of samples of midline abdominal skin, lower eyelid and cornea/sclera taken at post-mortem examination of I 0 0 horses, 0. cervicalis microfilariae were recovered from 48 animals. Although in the infected animals microfilariae were common in all 3 sites, it was found that horses with ocular invasion tended to have higher cutaneous concentrations than those without invasion of the eye suggesting that the occurrence of 0. cervicalis microfilariae in the equine eye is a simple "spillover" phenomenon. Since minimal pathological changes were associated with infection, the authors advise great caution before considering the presence of 0 . cervicalis microfilariae in diseased skin significant. Unfortunately, no study was made of the relationship between the presence of microfilariae in the eye and ocular pathology. Ant. J . vet. Res. 36, 1029-31. J. L. DUNCAN

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