Uncoupling of the pineal melatonin synthesis of rats from the circadian regulation.
We show that the pineal melatonin synthesis of rats can be uncoupled from the circadian regulation by exposing the animals to abnormally long light periods. Male rats were kept 7 days under 22.5/1.5-h light/dark conditions and then exposed to darkness at different times of the day. After a 60-min dark exposure, the melatonin synthesis increased independently of the time of the day (Expt. 1). During 22 h in darkness, the mean melatonin content did not return to the low daytime level (Expt. 2). A dark-induced, time-independent increase of melatonin was also found after the rats had been 3-7 days under constant light (Expts. 3 and 4).
Department of Physiology, University of Helsinki, Finland.
M L
ML
Laakso
T
T
Hätönen
A
A
Alila
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D003624:Darkness; D008297:Male; D008550:Melatonin / Q000096:biosynthesis*; D010507:Periodicity; D010870:Pineal Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000318:Adrenergic beta-Agonists; D008550:Melatonin