To compare different substrains of Sprague-Dawley 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.
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). The Sprague-Dawley substrain SD1 was considered magnetic field sensitive and used for comparison with other substrains.
Rats of DMBA experiments received the first application of DMBA (5 mg/rat) at the first day of magnetic field or sham exposure. Rats were administered 20 mg DMBA in four weekly doses.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
repeated daily exposure, 24 h/day, 7 days a week for 18 weeks
|
|
|
Exposure 2:
50 Hz
Exposure duration:
repeated daily exposure, 24 h/day, 7 days a week for 2 weeks
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | repeated daily exposure, 24 h/day, 7 days a week for 18 weeks |
| Additional info | horizontally polarized magnetic field |
| Exposure source | |
|---|---|
| Chamber | Three exposure chambers with room for four cages were used for exposure. Three identical but non-energized exposure chambers were located at the other side of the same room for sham exposure. |
| Additional info | Both exposed and sham control rats were administered with 4 weekly doses of 5 mg/rat DMBA (7,12-dimethylbenz(a)anthracene) in sesame oil. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 100 µT | effective value | measured | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | repeated daily exposure, 24 h/day, 7 days a week for 2 weeks |
| Additional info | horizontally polarized magnetic field |
| Exposure source |
|
|---|---|
| Additional info | In the morning of the last day of exposure, all the rats received an 50 mg/kg i.p injection of BrdUrd (bromodeoxyuridine). |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 100 µT | effective value | measured | - | - |
In contrast with SD1 rats, no enhanced cell proliferation was found after magnetic field exposure in SD2 rats. Magnetic field exposure significantly increased mammary tumor development and growth in SD1 but not in SD2 rats.
These findings indicate that the genetic background plays an important role in effects of magnetic field exposure. Different strains or substrains of rats may serve to evaluate the genetic factors underlying sensitivity to cocarcinogenic or tumor-promoting effects of magnetic field exposure.
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