Longitudinal melatonin production in female laboratory rats during 1997-2006: possible modulatory effects of changing solar activity.

Earlier we reported that the urinary excretion of 6-sulfatoxymelatonin (aMT6s) displayed seasonal rhythms in laboratory rats and hypothesized that the horizontal intensity H of the geomagnetic field may act as seasonal zeitgeber. To test this, long-term experiments were performed with female Sprague-Dawley rats. In experiment I (n=12: 1997-1999) nocturnal aMT6s displayed a winter-summer increase by 30% and a rhythm with a phase-length of 24 months peaking in July 1998. In experiment II (n=12; 1999-2000) the winter-summer increase amounted to 40%. The estimated rhythm had a phase-length of 18 months with a peak in September 2000. Compared to experiment I both the rhythm-adjusted mean (MESOR, + 28%) and amplitude (+68%) were elevated. In experiment III (n=30; 2003-2004) the winter-summer increment was just 20%. A circannual rhythm with a peak in April/May was found. The MESOR was 13% higher than in experiment I but the amplitude was depleted ( -14%). In experiment IV (n=15; 2005-2006) a slight winter-summer increase (+15%) was found and a low-amplitude rhythm of 24 months phase-length peaking in June 2006. The MESOR was similar to experiment I but the amplitude was depressed (-36%). These results demonstrate that female rats within two years of age show elevated aMT6s during summer/spring which supports our initial hypothesis. The apparent inter-experimental amplitude variation indicates the involvement of additional variables. Based on our initial hypothesis, we postulate an involvement of the solar cycle affecting H leading to year to year variations and present supportive analyses.

Influence of a 902.4 MHz GSM signal on the human visual system: investigation of the discrimination threshold.

The proximity of a mobile phone to the human eye raises the question as to whether radiofrequency (RF) electromagnetic fields (EMF) affect the visual system. A basic characteristic of the human eye is its light sensitivity, making the visual discrimination threshold (VDThr) a suitable parameter for the investigation of potential effects of RF exposure on the eye. The VDThr was measured for 33 subjects under standardized conditions. Each subject took part in two experiments (RF-exposure and sham-exposure experiment) on different days. In each experiment, the VDThr was measured continuously in time intervals of about 10 s for two periods of 30 min, having a break of 5 min in between. The sequence of the two experiments was randomized, and the study was single blinded. During the RF exposure, a GSM signal of 902.4 MHz (pulsed with 217 Hz) was applied to the subjects. The power flux density of the electromagnetic field at the subject location (in the absence of the subject) was 1 W/m(2), and numerical dosimetry calculations determined corresponding maximum local averaged specific absorption rate (SAR) values in the retina of SAR(1 g) = 0.007 W/kg and SAR(10 g) = 0.003 W/kg. No statistically significant differences in the VDThr were found in comparing the data obtained for RF exposure with those for sham exposure.