title: Age-dependent decline in acyl-ghrelin concentrations and reduced association of acyl-ghrelin and growth hormone in healthy older adults.
abstract: BACKGROUND
  Acyl-ghrelin is thought to have both orexigenic effects and to stimulate GH release. A possible cause of the anorexia of aging is an age-dependent decrease in circulating acyl-ghrelin levels.
  
  
  OBJECTIVE
  The purpose of the study was to compare acyl-ghrelin and GH concentrations between healthy old and young adults and to examine the relationship of acyl-ghrelin and GH secretion in both age groups.
  
  
  METHODS
  Six healthy older adults (age 62-74 y, body mass index range 20.9-29 kg/m(2)) and eight healthy young men (aged 18-28 y, body mass index range 20.6-26.2 kg/m(2)) had frequent blood samples drawn for hormone measurements every 10 minutes for 24 hours. Ghrelin was measured in an in-house, two-site sandwich ELISA specific for full-length acyl-ghrelin. GH was measured in a sensitive assay (Immulite 2000), and GH peaks were determined by deconvolution analysis. The acyl-ghrelin/GH association was estimated from correlations between amplitudes of individual GH secretory events and the average acyl-ghrelin concentration in the 60-minute interval preceding each GH burst.
  
  
  RESULTS
  Twenty-four-hour mean (±SEM) GH (0.48 ± 0.14 vs 2.2 ± 0.3 μg/L, P < .005) and acyl-ghrelin (14.7 ± 2.3 vs 27.8 ± 3.9 pg/mL, P < .05) levels were significantly lower in older adults compared with young adults. Twenty-four-hour cortisol concentrations were higher in the old than the young adults (15.1 ± 1.0 vs 10.6 ± 0.9 μg/dL, respectively, P < .01). The ghrelin/GH association was more than 3-fold lower in the older group compared with the young adults (0.16 ± 0.12 vs 0.69 ± 0.04, P < .001).
  
  
  CONCLUSIONS
  These results provide further evidence of an age-dependent decline in circulating acyl-ghrelin levels, which might play a role both in the decline of GH and in the anorexia of aging. Our data also suggest that with normal aging, endogenous acyl-ghrelin levels are less tightly linked to GH regulation.
authors.affiliation: Division of Endocrinology and Metabolism (R.N., L.S.F., J.L., S.S.P., B.D.G., M.O.T.), Department of Medicine, Center for Diabetes Technology (L.S.F.), and Department of Pharmacology (M.L.J.), University of Virginia, Charlottesville, Virginia 22908.
authors.forename: Ralf
authors.initials: R
authors.lastname: Nass
authors.forename: Leon S
authors.initials: LS
authors.lastname: Farhy
authors.forename: Jianhua
authors.initials: J
authors.lastname: Liu
authors.forename: Suzan S
authors.initials: SS
authors.lastname: Pezzoli
authors.forename: Michael L
authors.initials: ML
authors.lastname: Johnson
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Gaylinn
authors.forename: Michael O
authors.initials: MO
authors.lastname: Thorner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood*; D001823:Body Composition; D015992:Body Mass Index; D005260:Female; D054439:Ghrelin / Q000097:blood*; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000097:blood; D008297:Male; D008875:Middle Aged
chemical_list: D054439:Ghrelin; D007328:Insulin; D019382:Human Growth Hormone; D006854:Hydrocortisone