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Melatonin Secretion and Puberty in Female Lambs Exposed to Environmental Electric and Magnetic Fields

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BIOLOGY OF REPRODUCTION 49, 857-864 (1993)

Melatonin Secretion and Puberty in Female Lambs Exposed to Environmental Electric
and Magnetic Fields'


This study determined whether chronic exposure of female lambs to the electric and magnetic fields (EMF) of a high voltage
transmission line can alter pineal secretion of melatonin and the normal occurrence of puberty.

 

J.M. LEE, JR.,2 F. STORMSHAK, 3 J.M. THOMPSON, 3 P. THINESEN,3 LJ. PAINTER, 3 E.G. OLENCHEK,3 D.L. HESS,4
R. FORBES,5 and D.L. FOSTER6
Department of Animal Sciences,3 Oregon State University, Corvallis, Oregon 97331-6702
Oregon Regional Primate Research Center,4 Beaverton, Oregon 97006
Department of Biology,5 Portland State University, Portland, Oregon 97207-0751
Departments of Obstetrics and Gynecology and Biology and Reproductive Sciences Program6
The University of Michigan, Ann Arbor, Michigan 48109-0404

ABSTRACT

This study determined whether chronic exposure of female lambs to the electric and magnetic fields (EMF) of a high voltage
transmission line can alter pineal secretion of melatonin and the normal occurrence of puberty. Twenty female Suffolk lambs
were assigned randomly in equal numbers to a control and a treatment group. Treatment from 2 to 10 mo of age consisted of
continuous exposure within the electrical environment of a 500-kV transmission line (mean electric field 6 kV/m, mean magnetic
field 40 mG). Treated lambs were penned directly beneath the transmission line; control lambs were maintained in a pen of
similar construction 229 m from the line where EMF were at ambient levels (mean electric field < 10 V/m, mean magnetic
field < 0.3 mG). Melatonin was analyzed by RIA in serum of blood samples collected at 0.5-3-h intervals over eight 48-h periods.
To assess attainment of puberty, serum concentrations of progesterone were determined by RIA from blood samples collected
twice weekly beginning at 19 wk of age. Concentrations of circulating melatonin in control and treated lambs were low during
daylight hours and increased during nighttime hours. The characteristic pattern of melatonin secretion during nighttime (amplitude, phase, and duration) did not differ between control and treatment groups. Age at puberty and number of subsequent estrous cycles also did not differ between groups. These data suggest that chronic exposure of developing female sheep to 60-Hz environmental EMF does not affect the mechanisms underlying the generation of the circadian pattern of melatonin secretion or the mechanisms involved in the onset of reproductive activity.

INTRODUCTION

Since the mid-1970s, public and scientific interest in the possible biological effects of power-frequency (50 and 60
Hz) electric and magnetic fields (EMF) has continued to increase

  1. These fields are produced by all electrical
    equipment and devices, including household appliances and power lines. Various effects of EMF have been reported under
    laboratory conditions
  2. Several epidemiological studies also suggest an association between magnetic and/or
    electric fields and cancer in children living near high-current power lines and in men working around electric power
    facilities and equipment
  3. To date, however, no causal link between EMF and adverse health effects, including effects
    on fertility, has been established
  4. One biological effect of EMF that has received considerable attention is the large depression of nocturnal melatonin secretion in laboratory animals. Wilson et al.
  5. first reported a significant reduction in pineal melatonin in male

Accepted June 10, 1993.
Received April 7, 1993.

 

'This study was funded by American Electric Power Service Corp., Bonneville Power Administration, Houston Lighting and Power Co., Hydro-Quebec, Salt River Project, and Western Area Power Administration. A summary of the work was presented
at the First World Congress for Electricity and Magnetism in Biology and Medicine,June 1992, Lake Buena Vista, FL. D.L.H. was supported in part by NIH grants RR00163 and HD18185.


2Correspondence: Jack M. Lee, Jr., Bonneville Power Administration, P.O. Box
3621 (EFB), Portland, OR 97208. FAX: (503) 230-3984).
laboratory rats chronically exposed to 60-Hz electric fields.
Nocturnal melatonin concentrations also were reduced and the phase was delayed 1.4 h in young male and female rats
exposed to 60-Hz electric fields in utero and for the first 23 days after birth [6]. Other studies have found that acute
exposure to rapidly switched d-c magnetic fields [7] and to power-frequency magnetic fields [8, 9] can depress melatonin
concentrations significantly in laboratory animals. Some of the reported effects of power-frequency fields on melatonin
in laboratory animals occurred with field strengths comparable to those experienced by humans, livestock, and
wildlife when they are close to electric power lines. An effect of environmental EMF on melatonin could have important
implications for reproductive endocrinology, mental health, and carcinogenesis [10].

An important role of the pattern of melatonin secretion is to provide information about day length. In seasonal
breeding species such as sheep, melatonin plays a critical role in regulating the timing of the breeding season [11].
Treatments that alter key aspects of the melatonin signal in sheep can significantly affect the seasonal onset of reproductive
activity, including the timing of puberty (reviewed / Foster et al. [12]). In this connection it has been reported
that puberty was delayed in female lambs in which the pineal gland was removed [13] or denervated by superior

cervical ganglionectomy [14, 15]. Replacement therapy with precisely timed daily infusions of melatonin can
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