title: Maximal secretory capacity of somatotrope cells in obesity: comparison with GH deficiency.
abstract: OBJECTIVE
  To evaluate the maximal secretory capacity of somatotrope cells in obesity and to compare it with that in hypopituitaric patients with GH deficiency.
  
  
  METHODS
  Stimulation with GHRH. (1 microgram/kg i.v.), combined with arginine (ARG, 0.5 g/kg i.v.), which strongly potentiates the GH response to the neurohormone, likely inhibiting hypothalamic somatostatin. The reproducibility of the GH response to GHRH + ARG was evaluated in a second session.
  
  
  METHODS
  Forty-five patients with simple obesity (OB 11 male and 34 female, age 40.5 +/- 1.8 y, BMI 38.8 +/- 1.1 kg/m2), 49 patients with hypopituitarism (GHD, 23 male and 26 female, 43.6 +/- 2.4 y, 24.7 +/- 0.7 kg/m2) and 44 normal young volunteers (NS, 25 male and 19 female, 33.8 +/- 1.0 y, 21.6 +/- 0.3 kg/m2) were studied.
  
  
  METHODS
  GH levels were assayed by IRMA method, basally at -60 and 0 min, and than every 15 min up to +120 min. Basal IGF-I levels were assayed by RIA method, after acid-ethanol extraction.
  
  
  RESULTS
  IGF-I levels in OB were lower (P < 0.005) than those in NS but higher (P < 0.005) than those in GHD. Mean peak GH response to GHRH + ARG in OB was clearly lower than that in NS (P < 0.005) and higher (P < 0.005) than that in GHD. Sixty-percent OB and 100% GHD showed peak GH responses lower than the minimum normal limit in NS (16.5 micrograms/l) while 4% OB and only 53% GHD with GH responses lower than 3 micrograms/l, the limit under which GH replacement therapy of severe deficiency is allowed. Good intraindividual reproducibility of the GH response to GHRH + arginine test was present in all groups (OB: r = 0.78, P < 0.0001; GHD: r = 0.57, P < 0.003; NS: r = 0.74, P < 0.0001;.
  
  
  CONCLUSIONS
  The maximal secretory capacity of somatotrope cells is clearly less than normal in the obese but still more than is seen in GHD subjects. However, in about 50% of obese patients, the pituitary GH releasable pool overlaps with that of hypopituitaric patients with GH deficiency. Thus, even when the maximal secretory capacity of somatotrope cells is evaluated by a potent and reproducible provocative tests such as GHRH + arginine, overweight has to be taken in a great account as the cause of severely impaired GH response in patients with suspected GH deficiency.
authors.affiliation: Department of Internal Medicine, University of Turin, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Maccario
authors.forename: M R
authors.initials: MR
authors.lastname: Valetto
authors.forename: P
authors.initials: P
authors.lastname: Savio
authors.forename: G
authors.initials: G
authors.lastname: Aimaretti
authors.forename: C
authors.initials: C
authors.lastname: Baffoni
authors.forename: M
authors.initials: M
authors.lastname: Procopio
authors.forename: S
authors.initials: S
authors.lastname: Grottoli
authors.forename: S E
authors.initials: SE
authors.lastname: Oleandri
authors.forename: E
authors.initials: E
authors.lastname: Arvat
authors.forename: E
authors.initials: E
authors.lastname: Ghigo
mesh_terms: D000328:Adult; D001120:Arginine / Q000494:pharmacology; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D019382:Human Growth Hormone / Q000097:blood / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007018:Hypopituitarism / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000378:metabolism; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D019382:Human Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D001120:Arginine