60-Hz electric-field effects on pineal melatonin rhythms: time course for onset and recovery.

Rats exposed for 3 weeks to uniform 60-Hz electric fields of 39 kV/m (effective field strength) failed to show normal pineal gland circadian rhythms in serotonin N-acetyl transferase activity and melatonin concentrations. The time required for recovery of the melatonin rhythm after cessation of field exposure was determined to be less than 3 days. The rapid recovery suggests that the overall metabolic competence of the pineal is not permanently compromised by electric-field exposure, and that the circadian rhythm effect may be neuronally mediated.