Effect of melatonin on sleep and rectal temperature of young healthy evening types

The present study assessed in healthy nocturnal juveniles the presence or a bsence of the hypnotic action of exogenous melatonin and its effect on core temperature by oral administration of exogenous melatonin at a pharmacolog ically low dose 15 min before going to bed at the normal time. Both sleep l atency and the number of instances of waking up after falling asleep tended to decrease, while the amount of Stage 2 sleep increased significantly. Ho wever, no hypothermic action regarding the rectal temperature for changes i n the circadian phase were observed. According to those results, it is poss ible that exogenous melatonin has some direct hypnotic action on habitual n ight sleep, although the extent of this action is considered to be relative ly weak.