Effect of IGF-I administration on growth hormone secretion in obese subjects.
OBJECTIVE
The reduction of spontaneous and stimulated growth hormone (GH) secretion in obesity could reflect an increase of the inhibitory effect of insulin growth factor I (IGF-I) on somatotroph secretion.


METHODS
In the present study we aimed to verify the effect of low dose recombinant human IGF-I (20 microg/kg subcutaneously (s.c.) at 0 min) on 3 h-spontaneous GH secretion (mGHc, 0-180 min) and on the GH response to growth hormone releasing hormone (GHRH) (1 microg/kg i.v. at+180 min) in obesity.


METHODS
Five obese women with abdominal adiposity (OB, age, mean+/-s.e.m.: 31+/-7.13 y; BMI: 32.04+/-3.69 kg/m(2)) and eight age-matched lean women (NW, 28.3+/-1.2 y; 20.1+/-0.5 kg/m(2)) were studied.


RESULTS
The mGHc and GHRH-induced GH response in OB (1.0+/-0.7 microg/l; AUC(180-270 min): 688.6+/-202.4 microg/l min, respectively) were lower than in NW (2.6+/-0.8 microg/l, 1315.9+/-189.9 microg/l min, respectively, P<0.05). The administration of rhIGF-I increased circulating IGF-I levels in OB and NW to the same extent (339.0+/-50.39 and 420.3+/-30.5 microg/l, respectively). The rhIGF-I administration did not affect mGHc in OB or NW (1.1+/-0.9 and 3.2+/-1.0 microg/l, respectively) but inhibited (P<0.05) the GH response to GHRH in OB (324.2+/-153.1 microg/l) and NW (730.2+/-288.1 microg/l).


CONCLUSIONS
Our study shows that the administration of low dose rhIGF-I reduces the somatotroph responsiveness to GHRH in obesity as well as in normal subjects.
Tassone
F
F
Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Turin, C. so Dogliotti 14, 10126 Turin, Italy.
Gianotti
L
L
Lanfranco
F
F
Ganzaroli
C
C
Oleandri
S E
SE
Taliano
M
M
Muller
E E
EE
Ghigo
E
E
Maccario
M
M
D000328:Adult; D019540:Area Under Curve; D016022:Case-Control Studies; D005260:Female; D013006:Growth Hormone / Q000187:drug effects* / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000494:pharmacology*; D009765:Obesity / Q000378:metabolism*
D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone