INCONSISTENT SUPPRESSION OF NOCTURNAL PINEAL MELATONIN SYNTHESIS AND SERUM MELATONIN LEVELS IN RATS EXPOSED TO PULSED DC MAGNETIC-FIELDS

The purpose of these experiments was to determine whether the exposure of rats at night to pulsed DC magnetic fields (MF) would influence th e nocturnal production and secretion of melatonin, as indicated by pin eal N-acetyltransferase (NAT) activity (the rate limiting enzyme in me latonin production) and pineal and serum melatonin levels. By using a computer-driven exposure system, 15 experiments were conducted. MF exp osure onset was always during the night, with the duration of exposure varying from 15 to 120 min. A variety of field strengths, ranging fro m 50 to 500 mu T (0.5 to 5.0 G) were used with the bulk of the studies being conducted using a 100 mu T (1.0 G) field. During the interval o f DC MF exposure, the field was turned on and off at 1-s intervals wit h a rise/fall time constant of 5 ms. Because the studies were performe d during the night, all procedures were carried out under weak red lig ht (intensity of <5 mu W/cm(2)). At the conclusion of each study, a bl ood sample and the pineal gland were collected for analysis of serum m elatonin titers and pineal NAT and melatonin levels. The outcome of in dividual studies varied. Of the 23 cases in which pineal NAT activity, pineal melatonin, and serum melatonin levels were measured, the follo wing results were obtained; in 5 cases (21.7%) pineal NAT activity was depressed, in 2 cases (8.7%) studies pineal melatonin levels were low ered, and in 10 cases (43.5%) serum melatonin concentrations Were redu ced. Never was there a measured rise in any of the end points that wer e considered in this study. The magnitudes of the reductions were not correlated with field strength (i.e., no dose-response relationships w ere apparent), and likewise the reductions could not be correlated wit h the season of the year (experiments conducted at 12-month intervals under identical exposure conditions yielded different results). Durati on of exposure also seemed not to be a factor in the degree of melaton in suppression. The inconsistency of the results does not permit the c onclusion that pineal melatonin production or release are routinely in fluenced by pulsed DC MF exposure. In the current series of studies, a suppression of serum melatonin sometimes occurred in the absence of a ny apparent change in the synthesis of this indoleamine within the pin eal gland (no alteration in either pineal NAT activity or pineal melat onin levels). Because melatonin is a direct free radical scavenger, th e drop in serum melatonin could theoretically be explained by an incre ased uptake of melatonin by tissues that were experiencing augmented l evels of free radicals as a consequence of MF exposure. This hypotheti cal possibly requires additional experimental documentation. (C) 1998 Wiley-Liss, Inc.