title: Longitudinal melatonin production in female laboratory rats during 1997-2006: possible modulatory effects of changing solar activity.
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.
authors.affiliation: Center for Research in Medical and Natural Sciences, University of Tübingen, Tübingen, Germany.
authors.forename: Hella
authors.initials: H
authors.lastname: Bartsch
authors.forename: Dieter
authors.initials: D
authors.lastname: Mecke
authors.forename: Hansgeorg
authors.initials: H
authors.lastname: Probst
authors.forename: Heinz
authors.initials: H
authors.lastname: Küpper
authors.forename: Eckhard
authors.initials: E
authors.lastname: Seebald
authors.forename: Ilse
authors.initials: I
authors.lastname: Herget
authors.forename: Elmar
authors.initials: E
authors.lastname: Peschke
authors.forename: Lothar
authors.initials: L
authors.lastname: Salewski
authors.forename: Thilo
authors.initials: T
authors.lastname: Stehle
authors.forename: Christian
authors.initials: C
authors.lastname: Bartsch
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000652:urine; D002940:Circadian Rhythm / Q000528:radiation effects; D005260:Female; D060526:Magnetic Fields; D008550:Melatonin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000652:urine; D017440:Photoperiod; D010870:Pineal Gland / Q000378:metabolism* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012621:Seasons; D019445:Solar Activity; D013472:Sunlight; D013997:Time Factors
chemical_list: D015415:Biomarkers; C054513:6-sulfatoxymelatonin; D008550:Melatonin