Bioelectromagnetics 26:49^53 (2005)

Short Term Exposure to 1439 MHz PulsedTDMAField Does Not Alter Melatonin

Synthesis in Rats

Keisuke Hata,1,2* Hironori Yamaguchi,1 GiichirouTsurita,1 Soichi Watanabe,3 KanakoWake,3

MasaoTaki,4 Shoogo Ueno,2 and Hirokazu Nagawa1

1Department of Surgical Oncology, Faculty of Medicine,The University of Tokyo,Tokyo, Japan

2Department of Biomedical Engineering, Faculty of Medicine,The University of Tokyo,Tokyo, Japan

3National Institute of Information, Communications andTechnology,Tokyo, Japan4Department of Electrics and Information Engineering,TokyoMetropolitanUniversity,

Tokyo, Japan

Thewidespread use of the mobile phone has initiated many studies on the possible adverse effects of ahigh frequency electromagnetic field (EMF), which is used inmobile phones. A low frequency EMF isreported to suppress melatonin synthesis. The aim of this study was to clarify the effects on melatoninsynthesis in rats after short term exposure to a 1439MHz time divisionmultiple access (TDMA) EMF.The average specific absorption ratio (SAR) of the brain was 7.5 W/kg, and the average SARs of thewhole body were 1.9 and 2.0 W/kg for male and female rats, respectively. A total of 208 male andfemale rats were investigated. After acclimatization to a 12 h light–dark (LD) cycle, serum and pinealmelatonin levels together with pineal serotonin level under a dark condition (less than 1 lux) wereexamined by radioimmunoassay. No significant differences in melatonin and serotonin levels wereobserved between the exposure, sham, and cage control groups. These results suggest that short termexposure to a 1439MHz TDMAEMF, which is about four times stronger than that emitted by mobilephones, does not alter melatonin and serotonin synthesis in rats. Further investigations on the effects oflong term exposure are warranted. Bioelectromagnetics 26:49–53, 2005. � 2004 Wiley-Liss, Inc.

Key words: mobile telephony; microwave; melatonin; serotonin

INTRODUCTION

The mobile phone has been widely used in recentyears, and possible adverse effects of the high frequencyelectromagnetic field (EMF) emitted by mobile phoneshave become a public concern. We have reported that a1439MHz time divisionmultiple access (TDMA) EMFhas no effect on the permeability of the blood brainbarrier, brain morphology, body mass, or referencememory [Tsurita et al., 2000; Yamaguchi et al., 2003].

It was reported that low frequency EMF sup-pressedmelatonin synthesis [Wilson et al., 1981]. Kato,et al. reported that a 50Hz circularly polarizedmagneticfield decreases both the pineal and plasma melatoninlevel, whereas 50 Hz horizontal and vertical magneticfields do not [Kato et al., 1993, 1994a,b]. However, theeffect of high frequency EMF on melatonin synthesishas not been sufficiently investigated.

Melatonin is synthesized from serotonin in thepineal gland. Melatonin level shows a circadian rhythmin both rats and humans when subjected to a 12 h light–

dark (LD) cycle. The LD cycle causes blood and pinealbody melatonin levels to increase during the darkperiod and decrease during the light period. The supra-chiasmatic nucleus in the hypothalamus, which is con-sidered to be a major area controlling the internalclock, contains melatonin receptors, and the circadianrhythm is adjusted by melatonin. In addition, antioxi-dant activity, and carcinostatic property, the so-called

�2004Wiley-Liss, Inc.

——————Grant sponsor: Ministry of Internal Affairs and Communicationsin Japan.

*Correspondence to: Keisuke Hata, MD, Department of SurgicalOncology, Faculty of Medicine, The University of Tokyo, 7-3-1Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan.E-mail: khata-tky@umin.ac.jp

Received for review 8 March 2004; Final revision received 8 June2004

DOI 10.1002/bem.20080Published online in Wiley InterScience (www.interscience.wiley.com).

melatonin hypothesis, have also attracted attention [Coset al., 2002;Mayo et al., 2002; Pawlikowski et al., 2002;Poeggeler et al., 2002].

The aim of this studywas to investigate the effectson melatonin synthesis in rats after short term exposureto a 1439 MHz TDMA EMF, as used in mobile phonesin Japan.

MATERIALS AND METHODS

Exposure System and Conditions

We used the same carousel type exposure systemas used in previous studies [Tsurita et al., 2000;Yamaguchi et al., 2003]. This system consisted of asmall anechoic chamber, a round turntable with eighttubes, a quarter-wavelength monopole antenna on themetal floor, and a ventilation cylinder through theceiling. It could expose eight rats at the same time. A1439 MHz EMF TDMA signal for a Personal DigitalCellular (PDC) system (burst trains of pulses at 50 Hz,1/3 duty ratio, 6.7 ms pulse width) was fed to thequarter-wavelength monopole antenna. Rats in theexposure group were exposed from the beginning ofthe dark period for 4 h on 1 day. The average specificabsorption ratio (SAR) of the brain was 7.5 W/kg,and the average SARs of the whole body were 1.9 and2.0 W/kg for male rats (370 g) and for female ones(283 g), respectively. Those values were calculatedby the finite difference time domain method withnumerical rat models and validated by measuring thetemperature increase in the rat phantom [Watanabeet al., 1999a; Watanabe et al., 1999b].

Animals

A total of 104 male and 104 female Sprague–Dawley (SD) rats, 8–10 weeks old, were obtained fromCharles River Japan (Yokohama, Japan). They wereacclimatized to a 12h-12h LD cycle for at least 2 weeks,and were raised to 10–12 weeks old. The light periodbegan at 8 p.m. and ended at 8 a.m. (400 lux at the cagelevel), while the dark period (only dim red light) beganat 8 a.m. and ended at 8 p.m. (less than 1 lux). The LDcycle was reversed so as to perform this experimentduring the daytime as in a previous report [Vollrathet al., 1997]. Temperature and humidity were main-tained at 24� 2 8Cand 40� 5%, respectively. Food andwater were continuously available. This study wasapproved by the institutional board of review for animalcare.

The rats were divided into four groups, exposure(EM) (n¼ 64), sham (n¼ 64), cage control (n¼ 64),and light control (LC) (n¼ 16) group. Rats in the EMgroup were exposed to a 1439MHz TDMA field for 4 hon 1 day during the dark period (8 a.m. to noon). Those

in the sham group were placed in the exposure systemwithout TDMA exposure. Those in the cage controlgroup were not placed in the exposure system. Those inthe LC group were subjected to LD 12:12 for at least2 weeks as in the other three groups, and on the last day,were exposed to the light condition (400 lux) untilmeasurement.

Measurement

Blood and pineal gland were removed either at0:30 p.m. or 6:00 p.m. After the rats were anesthetized,blood was collected by cardiac puncture and serumwas frozen at �20 8C until assay. Then, the rats weredecapitated by guillotine, and the pineal body wasremoved and homogenized in 1 ml phosphate buffer(pH 6.0). After debris was removed by centrifugation,the supernatant was frozen at�20 8C until assay. Theseprocedures were performed under a dim red light(less than 1 lux) until the pineal body was removed.These sampleswere sent to SRL, Inc. (Tokyo, Japan) formeasurement of melatonin and serotonin by radio-immunoassay [Imaida et al., 2001].

Statistics

Statistica (Stat Soft, Inc., USA) was used forstatistical analysis. Analysis of variance with theNewman–Keul test was used to evaluate the differencesbetween the groups. A P value less than 0.05 wasconsidered to be statistically significant.

RESULTS

Melatonin Level

Both the pineal and serum melatonin levels wereunchanged after short term exposure to a 1439 MHzTDMA field (Fig. 1A–D) at the two time pointsinvestigated. Only the LC group, which was served asa positive control, showed a significant decrease inboth the pineal and serum melatonin levels as com-pared to the other three groups (P< 0.001). The resultsfrom the positive control supported the accuracy ofmeasurement.

Serotonin Level

The pineal serotonin level also remainedunchanged after short term exposure to a 1439 MHzTDMA field, whereas it increased in the LC group(Fig. 1E,F). The results from the positive control sup-ported the accuracy of measurement.

DISCUSSION

Both pineal and serum melatonin and serotoninlevels were unchanged by short term exposure to a

50 Hata et al.

Fig. 1. Melatonin and sertonin levels inmale and female rats after high frequency electromagneticfield exposure.There were no significant differences in each measurement among the exposure,sham, and cage control groups. Only the light control group, which was allocated as a positivecontrol, showedsignificant differencesascompared to the other threegroups (P< 0.001).A:Pinealmelatoninlevelinmalerats.B:Pinealmelatoninlevelin femalerats.C:Serummelatoninlevelinmalerats.D:Serummelatoninlevelin femalerats.E:Pinealserotoninlevelinmalerats.F:Pinealserotoninlevelin femalerats.

1439MHzTDMAField andMelatonin 51

1439 MHz TDMA EMF, as used in Japanese mobilephones, in male and female rats in our experimentalsetting. Although some authors reported that a lowfrequency EMF decreased serum and pineal melatoninlevels [Grota et al., 1994; Kato et al., 1994a], the effectsof a high frequency EMF on melatonin synthesis havenot been sufficiently investigated. A German groupreported that pineal and serum melatonin levels werenot altered by 6 h exposure to a 900 MHz EMF in rats[Mann et al., 1998]. Another German group reportedthat exposure to a 900 MHz EMF with whole bodyaveraged SAR of 0.06–0.36 W/kg had no short termeffect on pineal serotonin N-acetyl transferase (NAT)activity, or serummelatonin level [Vollrath et al., 1997].In that study, the whole bodies of the rats were exposedto 900 MHz TDMA signals (Global System for MobileCommunication). The exposure conditions are quitedifferent from those in this study where the heads of therats were exposed locally.

A few human studies regarding the effects of highfrequency EMF on melatonin synthesis have beenreported. The same group conducted a human rando-mized controlled study and confirmed that salivarymelatonin was not affected by 4 h exposure to 900MHzTDMA signals [Radon et al., 2001]. A Polish groupexamined effects of short term exposure to a 900 MHzEMF (SAR 1.23 W/kg) on urine 6-hydroxymelatoninsulfate in healthy young men [Bortkiewicz et al.,2002]. A French group examined the effects oflong term exposure to 900 or 1800 MHz EMF (SAR0.1–0.3 W/kg) on serum melatonin profile [de Sezeet al., 1999]. Neither of them showed significantdifferences with exposure to high frequency EMF.However, more studies are necessary to ascertain theeffects of high frequency EMF on melatonin synthesis.Our results confirmed and extended the finding thatshort term exposure to a high frequency EMF does notaffect melatonin synthesis.

The exposure system is blocked by an anechoicchamber, and the intensity of the light in the system isless than 1 lux. There is theoretically an unlimitednumber of combinations of the duration and timing ofexposure and the timing of sacrifice. In the presentstudy, rats were exposed to a TDMA EMF during thedark phase for the following reasons: (1) the effect ofTDMA exposure on melatonin synthesis is consideredto be maximal during the dark phase, as is the case withthat of light; (2) according to the white paper from theMinistry of Internal Affairs and Communications inJapan, mobile phones are used most frequently from9 p.m. to 11 p.m.

We measured pineal and serum melatonin levelssoon and 6 h after exposure to a TDMA EMF underthe dark condition, as representatives of the early and

late phases of the dark period. Since themeasurement ofpineal and serum melatonin requires sacrifice, sequen-tial melatonin levels or melatonin shift could not beevaluated in this experimental setting. The measure-ment of salivary melatonin level in humans is moresuited to this aim. On the other hand, an animal studyhas an advantage in that pineal melatonin level can bemeasured, which cannot be evaluated in a human study.Since melatonin is synthesized in the pineal body, thepineal melatonin level is considered to be moresensitive than the salivary melatonin level. In ourexperiment, melatonin and serotonin levels were deter-mined by radioimmunoassay. This assay was the sameas used in previous reports [Vaughan, 1993; Imaidaet al., 1998]. We also examined the LC group as apositive control and confirmed that the assay did workwell, since the activity of the rate-limiting enzyme,NAT, is reported to be lowered by light [Lewy et al.,1980].

There appears to be a gender difference in thenocturnal sensitivity of the pineal gland to light[Monteleone et al., 1995]. It is reported that womenshowed a 40% greater suppression of the nocturnalplasma melatonin level than men when exposed tobright light. Therefore, we investigated both male andfemale rats to look for a gender difference, but nosignificant difference was observed.

The average SAR of the brain at the exposure weused was 7.5 W/kg and the whole body averaged SARswere 1.9 W/kg and 2.0 W/kg for the male rats (370 g)and for the female rats (283 g), respectively. Local SARaveraged over 10 g of any tissues is restricted to below2W/kg in general public environments by law in Japan.Therefore, the SAR used in our experimental settingwas at least four times stronger than that used inJapanese mobile phones, and was considered to be highenough to evaluate the adverse effects of mobile phones.

Although no effects on melatonin synthesis wereobserved after short term exposure in this experimentduring dark phase, it is of interest for us to examine theeffects of long term exposure to high frequency EMFonmelatonin synthesis. Measurement during light phasemay be helpful to ascertain the effects of high frequencyEMF on melatonin profile in the future.

In conclusion, short term exposure to a 1439MHzTDMA EMF, as used in Japanese mobile phones, didnot alter melatonin and serotonin levels in rats. Furtherinvestigations of the effects of long term exposure arewarranted.

ACKNOWLEDGMENTS

We thank the members of the Committee toPromote Research on the Possible Biological Effects

52 Hata et al.

of Electromagnetic Fields, of the Ministry of InternalAffairs and Communications, Japan. We also thankNoboru Sunaga, Masahiro Hanazawa, and YukioYamanaka for technical assistance.

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