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 5 0-Hz sinusoidal magnetic field could influence serum melatonin concent ration and pineal enzymes activities in rats. The effects of both dura tion and intensity of exposure were also looked at. Two groups of Wist ar male rats were exposed to 50-Hz magnetic fields of either 1, 10 or 100 mu T. 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 und er a standard 12: 12 light : dark cycle with a temperature of 25 degre es C and a relative humidity of 45 to 50%. Control (Sham-exposed) anim als were kept in a similar environment but without exposure to a magne tic field. The animals were sacrificed under red dim light. Serum mela tonin concentration and pineal N-acetyltransferase (NAT) and hydroxyin dole-O-methyltransferase (HIOMT) activities were studied. Long-term ex posure to a magnetic field (10 and 100 mu T) significantly depressed t he nocturne peak of serum melatonin concentration and pineal NAT activ ity whereas no effect was observed on HIOMT activity. Shortterm exposu re depressed both pineal NAT activity and nocturnal serum melatonin co ncentration but only with the highest intensity used (100 mu T). Our r esults 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 intensit y of magnetic fields, 3) the sensitivity threshold to magnetic fields vary with the duration of exposure which strongly suggests a cumulativ e effect of sinusoidal magnetic fields on pineal function.