Exposure to a 50-Hz Magnetic Field Induces a Circadian Rhythm in 6-hydroxymelatonin Sulfate Excretion in Mice

The effect of magnetic field (MF) exposure on melatonin production was studied in female CD(2)F(1)(BALB/c x DBA/2) mice. The mice were exposed to a 50 Hz MF at 100 microT for 52 days and nocturnal urine was collected 1, 3, 7, 14, 16 and 23 days after the beginning of MF exposure. The animal room was illuminated for 12 h daily at 200 lux. To study the circadian rhythm of melatonin production, night and day samples of urine were collected once, at about 40 days after the beginning of MF exposure. Urinary 6-hydroxy melatonin sulfate (6-OHMS) was determined to assess melatonin production. The pineal glands were analyzed for melatonin content at the middle of the dark period. No statistically significant peak of melatonin was observed in either group. The light-regulated natural melatonin rhythm was absent in sham-exposed mice. The MF exposure caused a significant day-night difference in the 6-OHMS levels, but did not affect the total excretion of 6-OHMS during the 24-hour period. A possible interpretation of the findings is that MF exposure increases the sensitivity of the pineal gland to light in this strain normally insensitive to the circadian light variations. Further studies on interaction of light and MF exposure might help in understanding the inconsistencies of earlier research on MFs and melatonin.