Sinusoidal 50-Hz magnetic fields depress rat pineal NAT activity and serum melatonin. Role of duration and intensity of exposure.

The purpose of this study was to determine whether the exposure to a 50-Hz sinusoidal magnetic field could influence serum melatonin concentration and pineal enzymes activities in rats. The effects of both duration and intensity of exposure were also looked at. Two groups of Wistar male rats were exposed to 50-Hz magnetic fields of either 1, 10 or 100 microT. The first group was exposed for 12 hours and the second for 30 days (18 hours per day). During this time the animals were kept under a standard 12:12 light: dark cycle with a temperature of 25 degrees C and a relative humidity of 45 to 50%. Control (Sham-exposed) animals were kept in a similar environment but without exposure to a magnetic field. The animals were sacrificed under red dim light. Serum melatonin concentration and pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities were studied. Long-term exposure to a magnetic field (10 and 100 microT) significantly depressed the nocturne peak of serum melatonin concentration and pineal NAT activity whereas no effect was observed on HIOMT activity. Short-term exposure depressed both pineal NAT activity and nocturnal serum melatonin concentration but only with the highest intensity used (100 microT). Our results suggest that sinusoidal magnetic fields alter the production of melatonin through an inhibition of pineal NAT activity. Both duration and intensity of exposure play an important role in this effect. This work shows that, 1) sinusoidal magnetic field depresses NAT activity as static magnetic field does whereas HIOMT activity remains unaltered whatever the type of experiment and the intensity used, 2) the effect observed is related to both the duration of exposure and the intensity of magnetic fields, 3) the sensitivity threshold to magnetic fields vary with the duration of exposure which strongly suggests a cumulative effect of sinusoidal magnetic fields on pineal function.