title: Acute effects of melatonin administration on cardiovascular autonomic regulation in healthy men.
abstract: BACKGROUND
  Previous studies have suggested that melatonin, a major pineal hormone, possibly modulates the autonomic nervous system in animals. The aim of this study was to examine the effects of melatonin administration on heart rate variability (HRV) in human beings.
  
  
  METHODS
  In 26 healthy men, melatonin (2 mg) or placebo was randomly administered. Power spectral analysis of HRV and blood pressure monitoring were performed in the supine position before and 60 minutes after administration and in the standing position 60 minutes after administration. Plasma catecholamine levels were also assessed.
  
  
  RESULTS
  No differences in any baseline parameters were found between the two groups. Compared with placebo, melatonin administration within 60 minutes increased R-R interval, the square root of the mean of the squared differences between adjacent normal R-R intervals, high-frequency power, and low-frequency power of HRV and decreased the low-frequency to high-frequency ratio and blood pressure in the supine position (all P <.01). Plasma norepinephrine and dopamine levels in the supine position 60 minutes after melatonin administration were lower compared with placebo (P <.05 and P <.01, respectively). Standing up resulted in the decrease of HRV and the increase of blood pressure and plasma catecholamine levels in both administration groups, and the differences between the groups found in the supine position disappeared.
  
  
  CONCLUSIONS
  These findings indicate that melatonin administration increased cardiac vagal tone in the supine position in awake men. Melatonin administration also may exert suppressive effects on sympathetic tone.
authors.affiliation: Department of Cardiovascular Medicine, Kumamoto University School of Medicine, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nishiyama
authors.forename: H
authors.initials: H
authors.lastname: Yasue
authors.forename: Y
authors.initials: Y
authors.lastname: Moriyama
authors.forename: R
authors.initials: R
authors.lastname: Tsunoda
authors.forename: H
authors.initials: H
authors.lastname: Ogawa
authors.forename: M
authors.initials: M
authors.lastname: Yoshimura
authors.forename: K
authors.initials: K
authors.lastname: Kugiyama
mesh_terms: D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002319:Cardiovascular System / Q000187:drug effects / Q000294:innervation*; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D004298:Dopamine / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography / Q000187:drug effects; D016166:Free Radical Scavengers / Q000008:administration & dosage*; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D008550:Melatonin / Q000008:administration & dosage*; D009638:Norepinephrine / Q000097:blood; D011187:Posture / Q000502:physiology; D012016:Reference Values; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
chemical_list: D016166:Free Radical Scavengers; D008550:Melatonin; D004298:Dopamine; D009638:Norepinephrine