The circadian rhythm of melatonin production (high melatonin levels at night and low during the day) in the mammalian pineal gland is modified by visible portions of the electromagnetic spectrum, i.e., light, and reportedly by extremely low frequency (ELF) electromagnetic fields as well as by static magnetic field exposure. Both light and non-visible electromagnetic field exposure at night depress the conversion of serotonin (5HT) to melatonin within the pineal gland. Several reports over the last decade showed that the chronic exposure of rats to a 60 Hz electric field, over a range of field strengths, severely attenuated the nighttime rise in pineal melatonin production; however, more recent studies have not confirmed this initial observation. Sinusoidal magnetic field exposure also has been shown to interfere with the nocturnal melatonin forming ability of the pineal gland although the number of studies using these field exposures is small. On the other hand, static magnetic fields have been repeatedly shown to perturb the circadian melatonin rhythm. The field strengths in these studies were almost always in the geomagnetic range (0.2 to 0.7 Gauss or 20 to 70 mutesla) and most often the experimental animals were subjected either to a partial rotation or to a total inversion of the horizontal component of the geomagnetic field. These experiments showed that several parameters in the indole cascade in the pineal gland are modified by these field exposures; thus, pineal cyclic AMP levels, N-acetyltransferase (NAT) activity (the rate limiting enzyme in pineal melatonin production), hydroxyindole-O-methyltransferase (HIOMT) activity (the melatonin forming enzyme), and pineal and blood melatonin concentrations were depressed in various studies. Likewise, increases in pineal levels of 5HT and 5-hydroxyindole acetic acid (5HIAA) were also seen in these glands; these increases are consistent with a depressed melatonin synthesis. The mechanisms whereby non-visible electromagnetic fields influence the melatonin forming ability of the pineal gland remain unknown; however, the retinas in particular have been theorized to serve as magnetoreceptors with the altered melatonin cycle being a consequence of a disturbance in the neural biological clock, i.e., the suprachiasmatic nuclei (SCN) of the hypothalamus, which generates the circadian melatonin rhythm. The disturbances in pineal melatonin production induced by either light exposure or non-visible electromagnetic field exposure at night appear to be the same but whether the underlying mechanisms are similar remains unknown.
