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Low temperature stimulates pineal activity in Syrian hamsters.
K A Stokkan1, K O Nonaka, A Lerchl
1Department of Arctic Biology, University of Tromsøo, Norway.
Journal of Pineal Research
|January 1, 1991
Summary
Cold exposure significantly boosts melatonin production in Syrian hamsters, suggesting melatonin may mimic some cold effects. Brown adipose tissue enzyme activity, however, showed no change.
Area of Science:
- Endocrinology
- Chronobiology
- Environmental Physiology
Background:
- Melatonin, a key hormone in regulating circadian rhythms, is influenced by environmental factors like light and temperature.
- Cold exposure is known to affect metabolic rate and hormonal profiles in mammals.
- Pineal N-acetyltransferase (NAT) activity and melatonin levels exhibit daily rhythms, crucial for physiological adaptation.
Purpose of the Study:
- To investigate the impact of acute cold exposure on the daily rhythm of pineal N-acetyltransferase (NAT) activity and melatonin concentrations in Syrian hamsters.
- To examine the effect of cold exposure on the activity of type-II 5'-deiodinase (5'D) in brown adipose tissue (BAT).
- To explore the relationship between cold-induced hormonal changes and the potential for melatonin to simulate cold exposure effects.
Main Methods:
- Male Syrian hamsters, adapted to short days (LD 8:16), were exposed to cold (5°C) or warm (22°C) conditions for 24 hours.
- Pineal NAT activity, and pineal and serum melatonin concentrations were measured.
- Type-II 5'-deiodinase activity in brown adipose tissue (BAT) was assessed.
Main Results:
- Cold exposure significantly elevated nighttime peak levels of pineal NAT activity and both pineal and serum melatonin concentrations compared to warm-acclimated controls.
- Both melatonin and NAT activity demonstrated a clear circadian rhythm, with a peak during the late dark period.
- No significant difference in BAT type-II 5'-deiodinase activity was observed between cold- and warm-exposed hamsters, nor did it exhibit diel rhythmicity.
Conclusions:
- Acute cold exposure enhances melatonin production and NAT activity in Syrian hamsters, supporting the hypothesis that melatonin may mediate some effects of cold.
- The lack of response in brown adipose tissue 5'-deiodinase activity to cold exposure warrants further investigation.
- These findings contribute to understanding the interplay between environmental temperature, circadian rhythms, and hormonal regulation.