Effects of 60 Hz magnetic field exposure on the pineal and hypothalamic-pituitary-gonadal axis in the Siberian hamster (Phodopus sungorus)

Experiments using the dwarf Siberian hamster Phodopus sungorus were carried out to determine possible neuroendocrine consequences of one-time and repe ated exposures to 60 Hz magnetic fields (MF). Animals were maintained in ei ther a short-light (SL, 8 h light:16 h dark) or long-light (LL, 16 h light: 8 h dark) photoperiod. Acute tone-time, 15 min) exposure of male SL animals to a linearly polarized, horizontally oriented, 60 Hz MF (0.1 mT) gave ris e to a statistically significant (P < .005) reduction in pineal melatonin c ontent as determined 3 and 5 h after onset of darkness. In LL animals, acut e exposure to 0.10 mT resulted in a significant decrease in pineal melatoni n as measured 4 h after onset of darkness, whereas acute exposure to 50 mu T showed no effect compared with sham exposure. In SL animals, an increase in norepinephrine was observed in the medial basal hypothalamus (including the suprachiasmatic nucleus) after acute exposure (P < .01). Daily MF expos ure of SL animals to a combination of steady-state and on/off 60 Hz magneti c fields (intermittent exposure) at 0.1 mT for 1 h per day for 16 days was associated with a reduction in melatonin concentrations at 4 h after onset of darkness and an increase in blood prolactin concentrations (P < .05). Ex posure of SL animals to a steady state 60 Hz MF for 3 h/day for 42 days res ulted in a statistically significant reduction in body weight (ANOVA: P > . 05), compared with sham-exposed SL animals. At 42 days, however, no signifi cant changes in overnight melatonin or prolactin levels were detected. In b oth repeated exposure experiments, gonadal weights were lowest in the MF-ex posed groups. This difference was statistically significant (P (.05) after 42 days of exposure. These data indicate that both one-time and repeated ex posure to a 0.1 mT, 60 Hz MF can give rise to neuroendocrine responses in P hodopus. (C) 1999 Wiley-Liss, Inc.