title: Twenty-four-hour profiles of acylated and total ghrelin: relationship with glucose levels and impact of time of day and sleep.
abstract: BACKGROUND
  The acylation of ghrelin is essential for its stimulatory effects on GH release and appetite. Most of the physiology of ghrelin has been defined based on the assay of total ghrelin (TG), which mainly reflects levels of unacylated ghrelin. Whether levels of acylated ghrelin (AG) are influenced by circadian time and sleep and impact glucose regulation under physiologic conditions is not known.
  
  
  METHODS
  Blood was sampled at 10- to 30-min intervals for 24 h in 14 healthy young lean men under controlled conditions of activity, light-dark cycle, and sleep-wake schedule. The subjects ingested three identical carbohydrate-rich meals at 5-h intervals. Sleep was polygraphically monitored. Levels of TG and AG were measured by RIA. The 24-h profiles of glucose and insulin levels were assessed simultaneously.
  
  
  RESULTS
  Postprandial glucose concentrations were positively correlated with mean levels of AG but not TG, independently of insulin. Postprandial suppression and rebound of AG and TG occurred in parallel and were not impacted by time of day. The nocturnal elevation of AG and TG reflects the postdinner rebound curbed by an inhibitory effect of sleep. The ratio of AG to TG was lower during sleep than during wake, consistent with a reduction of orexigenic signal.
  
  
  CONCLUSIONS
  Individual differences in AG levels may be an important predictor of overall glucose control under physiological conditions. Sleep, but not time of day, impacts postprandial TG and AG responses. The inhibitory effect of sleep on ghrelin release and acylation is consistent with the association between sleeping and fasting.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale/Université Claude Bernard Lyon-Unité 628, Physiologie Intégrée du Système d'Éveil, Université Claude Bernard Lyon 1, 8 Avenue Rockefeller, 69373 Lyon Cedex 08, France. karine.spiegel@univ-lyon1.fr
authors.forename: Karine
authors.initials: K
authors.lastname: Spiegel
authors.forename: Esra
authors.initials: E
authors.lastname: Tasali
authors.forename: Rachel
authors.initials: R
authors.lastname: Leproult
authors.forename: Neal
authors.initials: N
authors.lastname: Scherberg
authors.forename: Eve
authors.initials: E
authors.lastname: Van Cauter
mesh_terms: D000215:Acylation; D000328:Adult; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000494:pharmacology; D005215:Fasting / Q000378:metabolism; D054439:Ghrelin / Q000097:blood*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D017286:Polysomnography; D019518:Postprandial Period / Q000502:physiology; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D054439:Ghrelin; D007328:Insulin