title: Diurnal variations of interleukin-6 plasma levels are confounded by blood drawing procedures.
abstract: Recent findings suggest that inflammatory cytokines are involved in sleep regulation. In part, this idea is based on studies showing that systemic levels of interleukin-6 (IL-6) are affected by sleep and sleep deprivation. However, intravenous (IV) catheters used for repetitive blood sampling were reported to increase local IL-6 production, which might confound sleep-dependent or circadian changes in the plasma concentrations of this cytokine. To further examine the effects of blood drawing procedures on IL-6 plasma levels, 12 healthy young male subjects participated in a 24-h cross-over study protocol involving sleep and sleep deprivation. Blood was collected half-hourly through an IV line and one additional sample was taken by a simple needle stick from the contralateral arm in parallel to the last sample from the catheter. Difficulties in blood sampling, the plasma levels of IL-6, cortisol and subjective sleepiness were quantified. In samples from the IV line there was a linear increase in IL-6 levels in both conditions, whereas the amount of IL-6 detected in the needle stick sample at the end did not differ from baseline. IL-6 levels were significantly higher in samples rated as difficult and those difficulties were more frequent during sleep compared to nocturnal wakefulness. IL-6 levels did not correlate to variations in sleepiness or cortisol levels. We conclude that variations in IL-6 plasma levels measured in samples from an IV catheter are caused, at least in part, by changes in local cytokine production rather than by physiological changes in circulating IL-6 levels.
authors.affiliation: Max Planck Institute of Psychiatry, Kraepelinstrasse 10, D-80804, Munich, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Haack
authors.forename: Thomas
authors.initials: T
authors.lastname: Kraus
authors.forename: Andreas
authors.initials: A
authors.lastname: Schuld
authors.forename: Mira
authors.initials: M
authors.lastname: Dalal
authors.forename: Dagmar
authors.initials: D
authors.lastname: Koethe
authors.forename: Thomas
authors.initials: T
authors.lastname: Pollmächer
mesh_terms: D000293:Adolescent; D000328:Adult; D001800:Blood Specimen Collection / Q000379:methods*; D002404:Catheterization; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D012890:Sleep / Q000502:physiology; D012892:Sleep Deprivation / Q000097:blood
chemical_list: D015850:Interleukin-6; D006854:Hydrocortisone