Acute 60 Hz magnetic field exposure effects on the melatonin rhythm in the pineal gland and circulation of the adult Djungarian hamster

Yellon SM. Acute 60Hz magnetic field exposure effects on the nucleation rhythm in the pineal gland and circulation of the adult Djungarian hamster. J. Pineal Res. 1994; 16: 136–144. Adult male and female hamsters in long days (16 hr of light) were exposed to a 1 gauss 60 Hz magnetic field for 15 min starting 2 hr before lights off. Sham‐exposed controls were placed in an adjacent exposure system but current was not applied. Hamsters were decapitated at 0.5–2 hr intervals from 1 hr before lights off to 1 hr after lights on (n = 4–6/clocktime/group); sera were harvested and pineal glands obtained for melatonin radioimmunoassay. In controls, pineal melatonin significantly increased from an average daytime baseline of less than 0.3 ng/gland to 3 ng/gland by 3 hr after lights off (P < 0.05, ANOVA). This increase was sustained for the duration of the night and returned to baseline within 1 hr after lights on. A similar melatonin rhythm was found in serum; concentrations ranged from 30 to 50 pg/ml at night and returned to a baseline of 12 pg/ml or less by 1 hr before lights on. The single magnetic field exposure reduced the duration and blunted the rise in the nocturnal melatonin rhythm. The study was then repeated in its entirety 6 months later. The same magnetic field treatment significantly suppressed pineal melatonin content at 5 hr after lights off and reduced serum melatonin concentrations at 3 and 5 hr after dark onset compared to sham‐exposed controls. Thus, the acute magnetic field exposure was again found to blunt the increase and suppress the duration of the nighttime melatonin rise. Point‐by‐point comparisons with the first study, however, did not replicate the magnetic field‐associated reduction in pineal melatonin content at 3 hr into the night, as well as in pineal and serum melatonin at 7. 5 hr after lights off. Concern about this divergence led us to repeat the experiment for a second time 6 months later. In both sham‐ and magnetic field‐exposed groups, melatonin increased within 3 hr after lights off and this rise was sustained until 0. 5 hr before lights on; nighttime melatonin content in the pineal gland was approximately 2 ng while in circulation melatonin concentrations averaged 60 pg/ml or less. No statistical differences were evident between the control and magnetic field exposed hamsters at any clocktime (P < 0. 05, ANOVA). Thus the absence of an effect of magnetic field exposure on the melatonin rhythm in either the pineal gland or circulation in this second replicate study contrasts with the clear suppression of the nocturnal melatonin rhythm in two previous experiments. Further work is needed to define the parameters of magnetic field exposure that consistently affect the pineal gland and its circadian melatonin rhythm. The time of the year for experimentation, animal age, or the endogenous response to exposure may be variables that might be understood before the physiological importance of magnetic fields for circadian time keeping mechanisms may be realized.