EMF Database abstract: SPONTANEOUS AND NITROSOUREA-INDUCED PRIMARY TUMORS OF THE CENTRAL NERVOUS SYSTEM IN FISCHER 344 RATS EXPOSED TO FREQUENCY-MODULATED MICROWAVE FIELDS.

EMF Database sample abstract

Last modified on: Monday, July 31, 2000
Copyright © 1994-2008, Information Ventures, Inc.

SPONTANEOUS AND NITROSOUREA-INDUCED PRIMARY TUMORS OF THE CENTRAL NERVOUS SYSTEM IN FISCHER 344 RATS EXPOSED TO FREQUENCY-MODULATED MICROWAVE FIELDS.
(Eng.) Adey, W. R.; Byus, C. V.; Cain, C. D.; Higgins, R. J.; Jones, R. A.; Kean, C. J.; Kuster, N.; MacMurray, A.; Stagg, R. B.; Zimmerman, G. [Dept. of Biochemistry, Boyce Hall, Room 1407, Univ. of California, Riverside, CA 92521, e-mail: RossAdey@citrus.ucr.edu (RR/W.R.A., C.V.B.); Univ. of California, Davis, CA 95616 (R.J.H.); Pettis Veterans Affairs Medical Center, Loma Linda, CA 92357 (C.D.C., R.A.J., C.J.K., A.M., R.B.S.); Swiss Federal Inst. of Technology, CH-8092 Zurich, Switzerland (N.K.); Loma Linda Univ. Sch. of Allied Health Professions, Loma Linda, CA 92350 (G.Z.)] Cancer Res 60(7):1857-1863; 2000
Funding: Motorola Corp.

The effects of lifetime exposure to a frequency modulated (FM) microwave signal on spontaneous and ethylnitrosourea- (ENU-) induced primary central nervous system (CNS) tumor incidence in a Fischer 344 rat model were studied. The purpose of the 2-yr bioassay was to test the hypothesis that FM microwave exposures that simulate RF radiation exposures to the head of an analog cellular telephone user might alter survival or the incidence of primary CNS tumors. The authors previously reported results of a companion study using a digital (TDMA) cell phone signal (Radiat Res 152:293-302, 1999; BENER Abstract No. 19823). A total of 102 pregnant Fischer 344 rats were randomly divided into 6 groups to be injected intravenously with 0 or 4 mg/kg ENU and to be sham exposed, irradiated with an FM 836.55-MHz +/- 12.5 kHz signal, or to serve as cage controls. Modulation of the 836.5-MHz signal was provided by a recorded pattern of balanced speech that presented all major speech components in a 2-min epoch that recycled continuously. ENU was administered on gestational day 18 and the 4-m/kg dose was selected to give an expected brain tumor incidence of 10 to 15% over the mean lifespan of 26 mo. The microwave exposures were provided by two systems. One system approximated far field (FF) conditions and provided initial exposures for the pregnant dams and after delivery for the offspring up to 21 days of age. Animal cages were positioned in a vertically oriented 3 X 3 matrix at the square aperture of the horn (2.0 m on a side). A power input of 37.2 W produced a plane wave with a mean field power density at the horn aperture of 2.6 mW/cm2. The horn was excited in a circular polarization to reduce the possibility of orientation-dependent coupling of microwave energy to the animals and the dams and pups were free to move about their cages. After weaning on postnatal day 33, weanlings were subjected to long-term intermittent exposure (2 hr/day, 4 days/wk) using a second system which produced a near-field (NF) exposure with the rats in individual restraints. The rats were confined in plastic tubular restraints and placed in a carousel that exposed 120 rats at a time, 10 rats each on 12 exposure platforms oriented radially around a central half-wave sleeved dipole antenna (Motorola Corp). Each rat faced the antenna at a fixed distance, 30 mm, measured from the tip of the nose for animals from weaning to 120 days of age, and 45 mm thereafter. SARs for the NF component of the experiment were estimated by a numerical dosimetric procedure described by Burkhardt et al. (Health Phys 73:770-778, 1997; BENER Abstract No. 16967) and by thermographic analysis of hemisected rat cadavers irradiated with a 235-W 836-MHz field for 90 sec. Whole-body averaged SARs for 150- to 450-g rats oriented with the 30-mm nose/antenna distance were 0.72 to 0.31 W/kg, respectively, while the corresponding SARs in the brain were calculated to be 1.1 to 1.6 W/kg. For the 45-mm nose/antenna distance, the whole-body SARs were 0.57 to 0.27 W/kg and the brain SARs varied from 0.74 to 1.2 W/kg. Thermographically measured SARs were somewhat higher: 1.8 W/kg in the brain of a 236-g rat at 45 mm nose/antenna distance, and 2.3 W/kg for a 462-g rat. A total of 778 pups were born and a total of 540 of these, 6 groups of 90 each with equal numbers of males and females, were entered into the NF component of the experiment. Survival was recorded and analyzed by the Kaplan-Meier statistic. The experiment was terminated over a 4-day period when the rats were 731-734 days of age when rats were killed and necropsied, the necropsies focusing on CNS tumors. Tumor incidences were tested statistically by the Z-statistic and the chi-squared test. ENU significantly decreased the mean survival of rats from the control group mean values of 706, 706, and 714 days to 632, 643, and 661 days (p<0.0005). No effects of FM microwave field exposure on survival were seen within the ENU-injected and untreated groups, i.e., for rats developing ENU-induced or spontaneous brain tumors. A total of 60 primary CNS tumors were found in all groups. Of these, 54 were glial tumors (48 in the brain and 6 in the spinal cord). No FM field-mediated increases in the number or incidence of either spontaneous or of ENU-induced brain tumors were seen. For example, the incidence of spontaneous brain tumors in all sham-irradiated and FM field irradiated groups was 1.1 and 4.4%, respectively, a nonsignificant difference (p=0.17). ENU treatment sharply increased the incidence of CNS tumors, from 1.1% to 14.4 to 22.2% (p<0.0001). No significant effect on ENU-induced tumor incidence attributable to FM field exposure was observed. A total of 168 rats died before the scheduled end of the study. Six major categories of probable cause of death were identified: (1) primary neural tumor; (2) primary neural tumor with hydrocephalus; (3) large granulocytic lymphocytic leukemia metastatic to the CNS; (4) extraneural tumor; (5) extraneural nontumor lesion; and (6) nontumor CNS lesion. There were no obvious differences within the ENU-treated or untreated groups in the distribution of cause of death, nor did FM field exposure modify the death rates. The authors concluded that these results provide no evidence that FM microwave fields simulating the electrical characteristics of analog cellular telephones have any effect on spontaneous or ENU-induced primary CNS tumors in Fischer 344 rats. In discussing these results, the authors maintain that these negative findings with FM fields contrast with their prevous results using standard digital phone fields pulsed on and off at 50/sec, where a trend was noted toward reduced incidence of both spontaneous and ENU-induced CNS tumors (Adey et al., 1999). They suggest that differences in the signaling structure of digital and FM fields may result in certain bioeffects induced by either amplitude-modulated or pulsed radiofrequency fields at athermal levels that are not seen with fields of similar average power but unvarying in intensity (continuous wave or frequency-modulated fields). (54 Refs). [Copyright 2000, Information Ventures, Inc.]

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