Effect of IGF-I administration on growth hormone secretion in obese subjects

Abstract

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.

DESIGN: In the present study we aimed to verify the effect of low dose recombinant human IGF-I (20 µg/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 µg/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/m²) and eight age-matched lean women (NW, 28.3±1.2 y; 20.1±0.5 kg/m²) were studied.

RESULTS: The mGHc and GHRH-induced GH response in OB (1.0±0.7 µg/l; AUC_{180–270 min}: 688.6±202.4 µg/l min, respectively) were lower than in NW (2.6±0.8 µg/l, 1315.9±189.9 µg/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 µg/l, respectively). The rhIGF-I administration did not affect mGHc in OB or NW (1.1±0.9 and 3.2±1.0 µg/l, respectively) but inhibited (P<0.05) the GH response to GHRH in OB (324.2±153.1 µg/l) and NW (730.2±288.1 µg/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.