Seasonal and Daily Variations in Plasma Melatonin in the High-Arctic Svalbard Ptarmigan (Lagopus mutus hyperboreus)

This study presents the daily rhythm of melatonin secretion throughout one year in a bird from the northern hemisphere, the Svalbard ptarmigan (Lagopus mutus hyperboreus), which lives naturally at 76-80°N. Eight Svalbard ptarmigan were caged outdoors at 70°N and blood sampled throughout one day each...

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Bibliographic Details
Published in:Journal of biological rhythms 1999-08, Vol.14 (4), p.314-319
Main Authors: Reierth, Eirik, Van’t Hof, Thomas J., Stokkan, Karl-Arne
Format: Article
Language:English
Subjects:
Animals
Animals, Wild - blood
Animals, Wild - physiology
Arctic Regions
Birds
Birds - blood
Birds - physiology
Circadian rhythm
Circadian Rhythm - physiology
Circadian Rhythm - radiation effects
Female
Hormones
Male
Melatonin - blood
Photoperiod
Seasons
Sunlight
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Summary:This study presents the daily rhythm of melatonin secretion throughout one year in a bird from the northern hemisphere, the Svalbard ptarmigan (Lagopus mutus hyperboreus), which lives naturally at 76-80°N. Eight Svalbard ptarmigan were caged outdoors at 70°N and blood sampled throughout one day each month for 13 months. At this latitude, daylight is continuous between May and August, but there is a short period of civil twilight around noon from late November to mid January. There was no daily rhythm in plasma melatonin in May-July. Plasma melatonin levels varied significantly throughout the day in all other months of the year, with the nighttime increase reflecting the duration of darkness. The highest mean plasma concentration occurred at midnight in March (110.1 ± 16.5 pg/ml) and represented the annual peak in estimated daily production. Around the winter solstice, melatonin levels were significantly reduced at noon and elevated during the nearly 18 h of consecutive darkness, and the estimated mean daily production of melatonin was significantly reduced. Thus, at the times of the year characterized by light-dark cycles, melatonin may convey information concerning the length of the day and, therefore, progression of season. The nearly undetectable low melatonin secretion in summer and the reduced amplitude and production in midwinter indicate a flexible circadian system that may reflect an important adaptation to life in the Arctic.
ISSN:0748-7304
1552-4531
DOI:10.1177/074873099129000731