To compare eight different strains and substrains of outbred and inbred rats in respect to magnetic field effects on cell proliferation in the mammary gland, susceptibility to DMBA-induced mammary cancer, and magnetic field effects on mammary tumor development and growth in the DMBA model. Furthermore, a magnetic field-sensitive inbred rat strain which is suited for genetic studies (such as backcrossing to identify genes responsible for magnetic field sensitivity) should be identified.
The authors suggest that genetic differences between substrains of Sprague-Dawley rats are involved in different results of different groups/laboratories on mammary tumor development (q.v. publication 4796). In contrast to Sprague-Dawley rats SD1, no enhanced cell proliferation and increased mammary tumor development was determined after magnetic field exposure in Sprague-Dawley rats SD2 (publication 13697).
In some experiments the effect of DMBA on cell proliferation in the mammary gland was determined.
|Exposure duration||continuously for 2 weeks|
In addition to the magnetic field-sensitive Sprague-Dawley substrain SD1 previously used in authors' experiments (see "related articles"), Fischer 344 rats were the only strain in which magnetic field exposure significantly enhanced BrdU labeling in the mammary epithelium, indicating a marked increase in cell proliferation. The magnetic field-induced increase in BrdU labeling in Fischer 344 rats was similar to that found after DMBA application.
Furthermore, analysis of mammary tissue from Fischer 344 rats revealed that exposure to magnetic field increased the number of terminal end buds, i.e. the site of origin of mammary carcinomas.
By comparison with magnetic field-insensitive inbred rat strains, Fischer 344 rats may serve to evaluate the genetic factors underlying sensitivity to cocarcinogenic or tumor-promoting effects of magnetic field irradiation.