title: Relationship between growth hormone (GH) status, serum leptin and body composition in healthy and GH deficient elderly subjects.
abstract: OBJECTIVE
  Growth hormone (GH) secretion declines with age and is affected by body composition. The signal that mediates the latter relationship remains III-defined. Leptin, the protein product of the adipocyte specific ob gene, is thought to accurately reflect fat mass and could therefore be a candidate to influence GH secretion. We have therefore investigated the relationship between GH status, leptin and body composition in normal and GH-deficient elderly subjects.
  
  
  METHODS
  GH Secretion was assessed by 20-minute sampling over 24 hours and serum leptin concentrations were measured in a single morning, fasted sample.
  
  
  METHODS
  Twenty-one GH deficient elderly patients (61-83 years) and 22 gender- and BMI-matched controls (61-88 years).
  
  
  METHODS
  Body composition was assessed by dual-energy X-ray absorptiometry (DEXA). GH was measured in an ultrasensitive chemiluminescent assay and serum leptin was determined by radio-immunoassay.
  
  
  RESULTS
  Leptin was correlated with percentage body fat in both sexes (male r = 0.75, female r = 0.89, both P < 0.001). Male patients had increased fat mass (FM) (P < 0.01) and leptin concentrations (P < 0.05) but similar lean mass (LM) compared with controls. However, leptin concentration per unit FM was identical in both groups (P = 0.3). In contrast, female patients had lower LM (P < 0.05) but similar FM to controls, yet their leptin concentration per unit FM was twice that of the controls (P < 0.05). In multiple linear regression (MLR) leptin was determined positively by FM and negatively by LM (controls r2 = 76%; patients r2 = 73%, both P < 0.0001). When controlled for gender, GH secretion in the controls was correlated negatively with leptin (r = -0.68, P < 0.01) and negatively with percentage body fat (r = -0.73, P < 0.01). In MLR, using leptin as a marker of body composition, 66% of the variability in GH secretion in the controls could be explained by gender (38%) and by leptin (28%).
  
  
  CONCLUSIONS
  Both decreased lean mass and increased fat mass raise serum leptin concentrations in normal and growth hormone-deficient elderly subjects. Leptin is therefore a marker of body composition rather than fat mass alone. The influence of body composition on growth hormone secretion in the elderly may be mediated through leptin, acting as a peripheral signal from adipose tissue to decrease GH secretion.
authors.affiliation: Department of Medicine, University of Manchester, UK.
authors.forename: M S
authors.initials: MS
authors.lastname: Gill
authors.forename: A A
authors.initials: AA
authors.lastname: Toogood
authors.forename: P A
authors.initials: PA
authors.lastname: O'Neill
authors.forename: J E
authors.initials: JE
authors.lastname: Adams
authors.forename: M O
authors.initials: MO
authors.lastname: Thorner
authors.forename: S M
authors.initials: SM
authors.lastname: Shalet
authors.forename: P E
authors.initials: PE
authors.lastname: Clayton
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000172:deficiency*; D006801:Humans; D020738:Leptin; D008297:Male; D008875:Middle Aged; D011506:Proteins / Q000378:metabolism*; D012044:Regression Analysis; D012737:Sex Factors
chemical_list: D020738:Leptin; D011506:Proteins; D013006:Growth Hormone