Carcinogenesis, Vol 19, 311-314, Copyright © 1998 by Oxford University Press
K Imaida, M Taki, T Yamaguchi, T Ito, S Watanabe, K Wake, A Aimoto, Y Kamimura, N Ito and T Shirai
The possible cancer promotion potential of local exposure to a pulse
modulated 929.2 MHz electromagnetic near-field on chemically-initiated rat
liver carcinogenesis was investigated employing a medium-term bioassay. A
929.2-MHz electromagnetic near-field of time division multiple access
(TDMA) signal for PDC (Personal Digital Cellular, Japanese cellular
telephone standard) system was directed to rats through a
quarter-wavelength monopole antenna. Maximum local specific absorption
rates (SARs) on temporal average were 7.2-6.6 W/kg within the whole body
and 2.0-1.7 W/kg within the liver, which was the target organ. The
whole-body average SARs on temporal average were 0.80-0.58 W/kg. Temporal
peak SARs had three times these values due to the duty ratio of the PDC
signal. Exposure was for 90 min a day, 5 days a week, over 6 weeks. The
exposure apparatus was specially designed for this experiment, to allow
exposure of the lateral mid-section of the rat body to the electromagnetic
near-field. Male F344 rats, 6 week-old, were initially (at week 0) given a
single dose of diethylnitrosamine (DEN, 200 mg/kg body wt, i.p.). At 2
weeks later, exposure (48 rats) or sham-exposure (48 rats) was started. The
exposure of electromagnetic near-fields was performed using the exposure
apparatus mentioned above. At week 3, all rats were subjected to a 2/3
partial hepatectomy. At week 8 (i.e. after 6 weeks exposure or
sham-exposure), the experiment was terminated and all rats were killed.
Carcinogenic potential was scored by comparing the numbers and areas of the
induced glutathione S- transferase placental form (GST-P) positive foci in
the livers of the exposed and sham-exposed rats. A further group of 24
animals, given only DEN and partial hepatectomy, served as the controls.
The numbers (no./cm2) of GST-P positive foci were 4.61 +/- 1.77, 5.21 +/-
1.92 (P < 0.05, versus control) and 4.09 +/- 1.47 and the areas
(mm2/cm2) were 0.30 +/- 0.16, 0.36 +/- 0.21 and 0.28 +/- 0.15, for the
exposed, sham- exposed and control groups, respectively. There were no
significant differences between the exposed and sham-exposed groups. These
findings clearly indicated that local body exposure to a 929.2-MHz field,
modulated in a PDC waveform, has no significant effect on rat liver
carcinogenesis under the experimental conditions employed.
ARTICLES
Lack of promoting effects of the electromagnetic near-field used for cellular phones (929.2 MHz) on rat liver carcinogenesis in a medium- term liver bioassay
Department of Pathology, Nagoya City University Medical School, Nagoya, Japan. imaida@med.nagoya-cu.ac.jp
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