This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Frisch, H. Articles by Schweitzer, K. Search for Related Content PubMed PubMed Citation Articles by Frisch, H. Articles by Schweitzer, K.

Increase in 6-Hydroxymelatonin Excretion in Humans during Ascent to High Altitudes

Department of Pediatrics (H.F., F.W., K.S.); Cancer Research Institute, Department of Epidemiology (T.W.); and Department of Ophthalmology (A.M.-E.), University of Vienna, 1090 Vienna, Austria; and Emergency and Outpatient Department, Patan Hospital (P.N.), Lalitpur, Nepal

Address all correspondence and requests for reprints to: Dr. Herwig Frisch, Department of Pediatrics, University Hospital Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. E-mail: herwig.frisch{at}meduniwien.ac.at.

Melatonin (MLT), the pineal gland hormone involved in the regulation of circadian rhythms, shows characteristic diurnal variation. Its physiological role in humans is not clear. Exposure to high altitudes may disrupt the circadian rhythm and lead to various endocrine changes. MLT in humans has not been studied under these conditions. Urinary 6-hydroxy-MLT sulfate (aMT6s) excretion was analyzed during the day (0700–2200 h) and night (2200–0700 h) phases. A cohort of 33 healthy volunteers, aged 19–65 yr, was studied during an ascent to a high altitude in the Himalayas on three occasions (at a lower altitude, at 3400 m, and after reaching maximal altitudes of 5600–6100 m). aMT6s excretion during the daytime remained unchanged during exposure to high altitudes. As expected, nocturnal values were higher than diurnal values at each point in time. However, there was a significant increase in nocturnal MLT excretion after the ascent to high altitudes. Ascent to high altitudes is associated with increased nocturnal excretion of aMT6s. The mechanism and physiological significance of this MLT increase are unclear.