Early evening melatonin and S-20098 advance circadian phase and nocturnal regulation of core body temperature

Am J Physiol. 1997 Apr;272(4 Pt 2):R1178-88. doi: 10.1152/ajpregu.1997.272.4.R1178.


The phase-shifting capacity and thermoregulatory effects of a single oral administration at 18 h of melatonin (5 mg) or S-20098, a melatonin agonist (5 or 100 mg), was investigated in eight healthy young men in a double-blind placebo crossover design. The unmasking conditions of a shortened constant-routine protocol (mini-CR) were used to collect evening phase markers of physiological parameters. In comparison to placebo, all three drug administrations induced an earlier dim-light melatonin onset (DLMO), an earlier increase in distal skin temperature, and an earlier decrease in core body temperature (CBT), heart rate, and proximal skin temperature. This indicates that administration at 18 h of both melatonin and S-20098 (more pronounced with 100 than 5 mg) induced an earlier regulation of the endogenous circadian nocturnal decline in CBT. On the posttreatment day a second mini-CR revealed persistent significantly phase-advanced circadian rhythms as estimated by DLMO, as well as by the midrange crossing time of CBT and heart rate decline. There were no significant differences between the two doses of S-20098. The data suggest that, in addition to immediate thermoregulatory changes, a phase advance of the circadian system had occurred and that the phase advance could still be measured on the posttreatment day.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetamides / administration & dosage
  • Acetamides / pharmacology*
  • Administration, Oral
  • Adult
  • Analysis of Variance
  • Body Temperature Regulation / drug effects*
  • Circadian Rhythm / drug effects*
  • Darkness
  • Double-Blind Method
  • Drug Administration Schedule
  • Heart Rate / drug effects
  • Humans
  • Hypnotics and Sedatives / administration & dosage
  • Hypnotics and Sedatives / pharmacology*
  • Light
  • Male
  • Melatonin / administration & dosage
  • Melatonin / agonists
  • Melatonin / pharmacology*
  • Periodicity*
  • Placebos
  • Random Allocation
  • Skin Temperature / drug effects


  • Acetamides
  • Hypnotics and Sedatives
  • Placebos
  • agomelatine
  • Melatonin