INCREASED RESORPTIONS IN CBA MICE EXPOSED TO LOW-FREQUENCY MAGNETIC-FIELDS - AN ATTEMPT TO REPLICATE EARLIER OBSERVATIONS

This paper has two aims. First, it reports the findings of a study on the effects of low-frequency magnetic fields on reproduction. Second, it serves as an example of an attempt to replicate the results of an e xperimental study in an independent laboratory and discusses some of t he problems of replication studies. To try to replicate the findings o f a study reporting increased resorptions (fetal loss) in mice exposed to 20 kHz magnetic fields with sawtooth waveform and to study the pos sible effects of 50 Hz sinusoidal fields, pregnant mice were exposed t o magnetic fields from day 0 to 18 of pregnancy, 24 h per day. The flu x densities of the vertical magnetic fields were 15 mu T (peak-to-peak ) at 20 kHz and 13 or 130 mu T (root mean square) at 50 Hz. Two strain s of animals were used: CBA/S mice imported from the laboratory report ing the original observations, and a closely related strain CBA/Ca. Th e CBA/S mice were cleaned of pathogenic microbes and parasites before they were imported into our laboratory. The magnetic field exposures d id not affect resorption rare in CBA/Ca mice. In CBA/S, the frequency of resorptions was higher in the exposed mice than in the control grou p. However, the increase was not significantly different from either t he no-effect hypothesis or the results of the original study we were a ttempting to replicate. Differences between the two studies and diffic ulties in interpreting the results are discussed. It is concluded that the results tend more to support than argue against increased resorpt ions in CBA/S mice exposed to the 20 kHz magnetic field. The results d emonstrate that animal strain is an important variable in bioelectroma gnetics research: even closely related strains may show different resp onses to magnetic field exposure. (C) 1997 Wiley-Liss, Inc.