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-l) on somatotroph secretion. DESIGN: In the present study we aimed to verify the effect of low dose reco mbinant human ICF-I (20 mug/kg subcutaneously (s.c.) at 0 min) on 3 h-spont aneous GH secretion (mGHc, 0-180 min) and on the CH response to growth horm one releasing hormone (GHRH) (1 mug/kg i.v. at + 180 min) in obesity. SUBJECTS: 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 +/- 1.2y; 20.1 +/- 0.5 kg/m2) were studied. RESULTS: The mGHc and GHRH-induced GH response in OB (1.0 +/- 0.7 mug/l; AU C(180-270min): 688.6 +/- 202.4 mug/l min, respectively) were lower than in NW (2.6 +/- 0.8 mug/l, 1315.9 +/- 189.9 mug/l min, respectively, P < 0.05). The administration of rhlGF-I increased circulating IGF-I levels in OB and NW to the same extent (339.0 +/- 50.39 and 420.3 +/- 30.5 mug/l, respectiv ely). The rhlGF-I administration did not affect mGHe in OB or NW (1.1 +/- 0 .9 and 3.2 +/- 1.0 mug/l, respectively) but inhibited (P < 0.05) the CH res ponse to GHRH in OB (324.2 +/- 153.1 mug/l) and NW (730.2 +/- 288.1 mug/l). CONCLUSIONS: Our study shows that the administration of low dose rhlGF-I re duces the somatotroph responsiveness to GHRH in obesity as well as in norma l subjects.