CONTEXT: In obesity, total IGF-I is not reduced to the degree predicted by low GH levels, and free IGF-I levels are normal to high. Total and free IGF-I may not reflect IGF-I biological activity because immunoassays cannot account for the modifying effects of IGF binding proteins on interactions between IGF-I and its receptor. OBJECTIVE: The aim of the study was to investigate the biological activity of IGF-I in obesity. DESIGN AND SETTING: We conducted a cross-sectional study at a General Clinical Research Center. STUDY PARTICIPANTS: Thirty-four healthy women (11 lean, 12 overweight, and 11 obese) of comparable age (overall mean, 30.7 +/- 1.3 yr) participated in the study. INTERVENTION: There were no interventions. MAIN OUTCOME MEASURES: We measured bioactive IGF-I (as measured by a kinase receptor activation assay), IGFBP-1, and GH using 6-h pools of serum collected every 10 min for 24 h, and fasting IGF-I and IGFBP-3. RESULTS: Mean 24-h GH (R = -0.76; P < 0.0001), total IGF-I (R = -0.36; P = 0.040), and IGFBP-1 (R = -0.41; P = 0.017) levels were inversely associated with BMI, whereas bioactive IGF-I and IGFBP-3 levels were not. Mean bioactive IGF-I was similar in the groups [2.72 +/- 0.22 (lean), 3.10 +/- 0.32 (overweight), and 2.43 +/- 0.23 [corrected] (obese) microg/liter; overall P = 0.22]. Percentage bioactive IGF-I [(bioactive/total IGF-I) x 100] was higher in obese subjects than both lean and overweight subjects (P = 0.039). CONCLUSIONS: Despite low GH secretion in obesity and decreasing IGFBP-1 with increasing BMI, 24-h mean bioactive IGF-I levels are not reduced in obese women and do not correlate with BMI or IGFBP-1 levels. This argues against elevated bioactive IGF-I as the etiology of reduced GH secretion through a feedback mechanism in obesity.
CONTEXT: In obesity, total IGF-I is not reduced to the degree predicted by low GH levels, and free IGF-I levels are normal to high. Total and free IGF-I may not reflect IGF-I biological activity because immunoassays cannot account for the modifying effects of IGF binding proteins on interactions between IGF-I and its receptor. OBJECTIVE: The aim of the study was to investigate the biological activity of IGF-I in obesity. DESIGN AND SETTING: We conducted a cross-sectional study at a General Clinical Research Center. STUDY PARTICIPANTS: Thirty-four healthy women (11 lean, 12 overweight, and 11 obese) of comparable age (overall mean, 30.7 +/- 1.3 yr) participated in the study. INTERVENTION: There were no interventions. MAIN OUTCOME MEASURES: We measured bioactive IGF-I (as measured by a kinase receptor activation assay), IGFBP-1, and GH using 6-h pools of serum collected every 10 min for 24 h, and fasting IGF-I and IGFBP-3. RESULTS: Mean 24-h GH (R = -0.76; P < 0.0001), total IGF-I (R = -0.36; P = 0.040), and IGFBP-1 (R = -0.41; P = 0.017) levels were inversely associated with BMI, whereas bioactive IGF-I and IGFBP-3 levels were not. Mean bioactive IGF-I was similar in the groups [2.72 +/- 0.22 (lean), 3.10 +/- 0.32 (overweight), and 2.43 +/- 0.23 [corrected] (obese) microg/liter; overall P = 0.22]. Percentage bioactive IGF-I [(bioactive/total IGF-I) x 100] was higher in obese subjects than both lean and overweight subjects (P = 0.039). CONCLUSIONS: Despite low GH secretion in obesity and decreasing IGFBP-1 with increasing BMI, 24-h mean bioactive IGF-I levels are not reduced in obesewomen and do not correlate with BMI or IGFBP-1 levels. This argues against elevated bioactive IGF-I as the etiology of reduced GH secretion through a feedback mechanism in obesity.
Authors: N R Musolino; M B Da Cunha Neto; R Marino Júnior; D Giannella-Neto; M D Bronstein Journal: Clin Endocrinol (Oxf) Date: 1999-04 Impact factor: 3.478
Authors: A Lukanova; E Lundin; A Zeleniuch-Jacquotte; P Muti; A Mure; S Rinaldi; L Dossus; A Micheli; A Arslan; P Lenner; R E Shore; V Krogh; K L Koenig; E Riboli; F Berrino; G Hallmans; P Stattin; P Toniolo; R Kaaks Journal: Eur J Endocrinol Date: 2004-02 Impact factor: 6.664
Authors: J O Jørgensen; N Vahl; T B Hansen; C Skjaerbaek; S Fisker; H Orskov; C Hagen; J S Christiansen Journal: Clin Endocrinol (Oxf) Date: 1998-04 Impact factor: 3.478
Authors: D J Brick; A V Gerweck; E Meenaghan; E A Lawson; M Misra; P Fazeli; W Johnson; A Klibanski; K K Miller Journal: Eur J Endocrinol Date: 2010-05-25 Impact factor: 6.664
Authors: S Jakobsdottir; I C van Nieuwpoort; C C van Bunderen; M B de Ruiter; J W R Twisk; J B Deijen; D J Veltman; M L Drent Journal: Int J Obes (Lond) Date: 2016-05-24 Impact factor: 5.095
Authors: Takara L Stanley; Meghan N Feldpausch; Caitlin A Murphy; Steven K Grinspoon; Hideo Makimura Journal: Growth Horm IGF Res Date: 2013-11-15 Impact factor: 2.372