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

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.(ABSTRACT TRUNCATED AT 250 WORDS)