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. Twenty female Suffolk lambs were assigned randomly in equal n umbers to a control and a treatment group. Treatment from 2 to 10 mo o f age consisted of continuous exposure within the electrical environme nt of a 500-kV transmission line (mean electric field 6 kV/m, mean mag netic field 40 mG). Treated lambs were penned directly beneath the tra nsmission line; control lambs were maintained in a pen of similar cons truction 229 m from the line where EMF were at ambient levels (mean el ectric field < 10 V/m, mean magnetic field < 0.3 mG). Melatonin was an alyzed 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 conce ntrations of progesterone were determined by RIA from blood samples co llected twice weekly beginning at 19 wk of age. Concentrations of circ ulating melatonin in control and treated lambs were low during dayligh t hours and increased during nighttime hours. The characteristic patte rn of melatonin secretion during nighttime (amplitude, phase, and dura tion) did not differ between control and treatment groups. Age at pube rty and number of subsequent estrous cycles also did not differ betwee n groups. These data suggest that chronic exposure of developing femal e sheep to 60-Hz environmental EMF does not affect the mechanisms unde rlying the generation of the circadian pattern of melatonin secretion or the mechanisms involved in the onset of reproductive activity.