Title:Longitudinal Melatonin Production in Female Laboratory Rats During 1997-2006: Possible Modulatory Effects of Changing Solar Activity
Volume: 5
Issue: 3
Author(s): Hella Bartsch, Dieter Mecke, Hansgeorg Probst, Heinz Kupper, Eckhard Seebald, Ilse Herget, Elmar Peschke, Lothar Salewski, Thilo Stehle and Christian Bartsch
Affiliation:
Keywords:
Geomagnetic field, melatonin, seasonal, solar activity, 6-sulfatoxymelatonin, zeitgeber, Sprague-Dawley rats, rhythm, winter-summer, phase-length
Abstract: 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.
