The administration of exogenous melatonin during the daytime lowers the thermoregulatory setpoint in humans

(1) The present study was conducted to explore the influence of melatonin administration during the daytime on both tympanic temperature (T-ty) level and the T-ty threshold for autonomic thermoregulation. (2) Melatonin administration at 11:00 h (3-mg oral dose) caused a rapid T-ty reduction. (3) After melatonin administration, cutaneous vasodilation and local sweating of the forearm occurred at significantly lower T-ty than after the placebo during the local body warming with hot water bath at 42degreesC. (4) Our results show that the melation administration during the daytime lowers the thermoregulatory setpoint in humans. (C) 2002 Elsevier Science Ltd. All rights reserved.