Effects of exposure to a circularly polarized 50‐Hz magnetic field on plasma and pineal melatonin levels in rats

We sought to determine whether a 6‐week exposure to a 50‐Hz rotating magnetic field influences melatonin synthesis by 11–18 week‐old Wistar‐King male rats. Rats were exposed continuously to a rotating magnetic field at 1, 5, 50, or 250 μT (spatial vector rms) for 6 weeks, except for twice‐weekly breaks of about 2 h for cleaning of cages and feeding. The rats were housed in exposure and sham‐exposure facilities, which were located in the same room, under a 12:12 light‐dark photoperiod (lights on at 06:00 h). The room was constantly illuminated by 4 small, dim red lights (< 0.07 lux in dark period). Levels of plasma and pineal gland melatonin were determined by radioimmunoassay. A significant decrease of melatonin was observed between the control group and groups exposed to a magnetic field at a flux density in excess of l μT during the night time, but no statistical differences were found among the exposed groups. These results indicate that subchronic exposure of albino rats to a 50‐Hz rotating magnetic field influences melatonin production and secretion by the pineal gland. © 1993 Wiley‐Liss, Inc.