title: The effect of prolonged fasting on levels of growth hormone-binding protein and free growth hormone.
abstract: OBJECTIVE
  There are limited data on growth hormone-binding protein (GHBP) and free GH levels during the physiological challenge of a prolonged fast. Our aim was to explore the relationships between GHBP, free GH, total GH and non-esterified fatty acid (NEFA) levels during overnight and 24-hour fasts in healthy young adults.
  
  
  METHODS
  We measured nocturnal levels of GHBP at three time-points (22:00, 03:00, 08:00), NEFA every 60 min and ultra-filtered free GH and total GH at 15-minute intervals for 10 h (22:00-08:00) during an overnight and a 24-hour fast in 7 female and 4 male normal-weight subjects aged 24.8 years (range: 22.8-26.9) with BMI 22.5 kg/m² (range: 18-27).
  
  
  RESULTS
  Spontaneous free and total GH levels were closely related during the overnight and 24-hour fasts (r=0.99, p<0.0001 and r=0.99, p<0.0001 respectively). 24 h of fasting led to an increase in levels of basal free GH (p=0.03), mean free GH (p=0.04), mean total GH (p=0.04) and NEFA (p<0.0001) whilst GHBP levels remained similar (p=0.8). Percentage free (over total) GH was similar during the overnight and prolonged fasts (p=0.3). There were no associations between levels of NEFA and free (r=0.24, p=0.5) or total GH (r=0.20, p=0.6).
  
  
  CONCLUSIONS
  A 24-hour fast led to parallel increases in free and total GH levels whilst there was no discernable change in GHBP levels or the fraction of free GH. This suggests that GHBP plays a role in limiting variations of circulating free GH levels. NEFA levels increased during the prolonged fast but they were not correlated with free or total GH levels.
authors.affiliation: University Department of Paediatrics, Institute of Metabolic Science, University of Cambridge, UK. burak@cantab.net
authors.forename: B
authors.initials: B
authors.lastname: Salgin
authors.forename: M L
authors.initials: ML
authors.lastname: Marcovecchio
authors.forename: N
authors.initials: N
authors.lastname: Hill
authors.forename: D B
authors.initials: DB
authors.lastname: Dunger
authors.forename: J
authors.initials: J
authors.lastname: Frystyk
mesh_terms: D000328:Adult; D002352:Carrier Proteins / Q000378:metabolism*; D004952:Esters / Q000737:chemistry*; D005215:Fasting; D005260:Female; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology; D008066:Lipolysis; D008297:Male; D008954:Models, Biological; D013997:Time Factors; D056928:X-Ray Absorption Spectroscopy / Q000379:methods
chemical_list: D002352:Carrier Proteins; D004952:Esters; D019382:Human Growth Hormone; C051815:somatotropin-binding protein