This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nyomba, B. L. G. Articles by Murphy, L. J. Search for Related Content PubMed PubMed Citation Articles by Nyomba, B. L. G. Articles by Murphy, L. J.

Free Insulin-Like Growth Factor I (IGF-I) in Healthy Subjects: Relationship with IGF-Binding Proteins and Insulin Sensitivity

Departments of Internal Medicine and Physiology, University of Manitoba, Winnipeg, Manitoba, Canada R3A 1R9

Address all correspondence and requests for reprints to: Dr. B. L. Gregoire Nyomba, Section of Endocrinology and Metabolism, Health Sciences Center, 820 Sherbrook Street GG449, Winnipeg, Manitoba, Canada R3A 1R9.

The majority of insulin-like growth factor I (IGF-I) circulates in blood bound to a family of IGF-binding proteins (IGFBPs). Only a small fraction of IGF-I is unbound or free, and one of the postulated roles of the IGFBPs is regulation of this free component, thereby increasing IGF-I bioavailability. Whether free IGF-I plays a physiological role in glucose homeostasis, however, is not clear. In this study, we examined the effects of acute changes in serum insulin on free IGF-I, total IGF-I, IGFBP-1, and IGFBP-3 in 11 healthy subjects. Glucose (0.3 g/kg) and insulin (0.05 U/kg) were injected iv at 0 and 20 min, respectively. Blood samples were drawn at defined intervals for 3 h, and insulin sensitivity (S_I) was computed by Bergman’s minimal model. Serum insulin reached a first peak after glucose injection and a second, higher peak after exogenous insulin administration. Although the total IGF-I level remained constant for the duration of the experiment, free IGF-I decreased by 20% 20 min after the first insulin peak and by 35% 20 min after the second peak. IGFBP-1 first declined to 20% below basal, then rose to 3-fold the basal level. IGFBP-3 increased linearly to 20% above basal by the end of the experiment, and this increase mirrored the decline of free IGF-I. In the fasting state, free IGF-I was positively correlated with S_I (r = 0.52; P < 0.005) and inversely correlated with glucose (r = -0.51; P < 0.005) and IGFBP-1 (r = -0.65; P < 0.001). In conclusion, free IGF-I is acutely regulated by insulin and correlates with S_I, suggesting that it may play a physiological role in glucose homeostasis.

This article has been cited by other articles:

				D. Choi, K.-T. T. Nguyen, L. Wang, S. A. Schroer, A. Suzuki, T. W. Mak, and M. Woo Partial Deletion of Pten in the Hypothalamus Leads to Growth Defects that Cannot be Rescued by Exogenous Growth Hormone Endocrinology, September 1, 2008; 149(9): 4382 - 4386. [Abstract] [Full Text] [PDF]

				M. P. Sperandeo, P. Annunziata, A. Bozzato, P. Piccolo, L. Maiuri, M. D'Armiento, A. Ballabio, G. Corso, G. Andria, G. Borsani, et al. Slc7a7 disruption causes fetal growth retardation by downregulating Igf1 in the mouse model of lysinuric protein intolerance Am J Physiol Cell Physiol, July 1, 2007; 293(1): C191 - C198. [Abstract] [Full Text] [PDF]

				C. J Bailey Treating insulin resistance: future prospects Diabetes and Vascular Disease Research, March 1, 2007; 4(1): 20 - 31. [Abstract] [PDF]

				E. K. Wei, J. Ma, M. N. Pollak, N. Rifai, C. S. Fuchs, S. E. Hankinson, and E. Giovannucci C-Peptide, Insulin-like Growth Factor Binding Protein-1, Glycosylated Hemoglobin, and the Risk of Distal Colorectal Adenoma in Women. Cancer Epidemiol. Biomarkers Prev., April 1, 2006; 15(4): 750 - 755. [Abstract] [Full Text] [PDF]

				J. Lin, P. M. Ridker, N. Rifai, I-M. Lee, J. E. Manson, J. E. Buring, and S. M. Zhang A Prospective Study of Hemoglobin A1c Concentrations and Risk of Breast Cancer in Women. Cancer Res., March 1, 2006; 66(5): 2869 - 2875. [Abstract] [Full Text] [PDF]

				E. K. Wei, J. Ma, M. N. Pollak, N. Rifai, C. S. Fuchs, S. E. Hankinson, and E. Giovannucci A Prospective Study of C-Peptide, Insulin-like Growth Factor-I, Insulin-like Growth Factor Binding Protein-1, and the Risk of Colorectal Cancer in Women Cancer Epidemiol. Biomarkers Prev., April 1, 2005; 14(4): 850 - 855. [Abstract] [Full Text] [PDF]

				J. Manetta, J. F. Brun, L. Maimoun, A. Callis, C. Prefaut, and J. Mercier Effect of training on the GH/IGF-I axis during exercise in middle-aged men: relationship to glucose homeostasis Am J Physiol Endocrinol Metab, November 1, 2002; 283(5): E929 - E936. [Abstract] [Full Text] [PDF]

				J. Nygren, C. Carlsson-Skwirut, K. Brismar, A. Thorell, O. Ljungqvist, and P. Bang Insulin infusion increases levels of free IGF-I and IGFBP-3 proteolytic activity in patients after surgery Am J Physiol Endocrinol Metab, October 1, 2001; 281(4): E736 - E741. [Abstract] [Full Text] [PDF]

				J. K. Cruickshank, A. H. Heald, S. Anderson, J. E. Cade, J. Sampayo, L. K. Riste, A. Greenhalgh, W. Taylor, W. Fraser, A. White, et al. Epidemiology of the Insulin-like Growth Factor System in Three Ethnic Groups Am. J. Epidemiol., September 15, 2001; 154(6): 504 - 513. [Abstract] [Full Text] [PDF]

				A. Ferreira, A. Ghazali, J. Galvao, J.-C. Souberbielle, P. M. Jehle, S. Mohan, B. Descamps-Latscha, R. Oprisiu, A. Fournier, and T. B. Drueke Effect of type of dialysis membrane on bone in haemodialysis patients Nephrol. Dial. Transplant., June 1, 2001; 16(6): 1230 - 1238. [Abstract] [Full Text] [PDF]

				P. Stattin, A. Bylund, S. Rinaldi, C. Biessy, H. Dechaud, U.-H. Stenman, L. Egevad, E. Riboli, G. Hallmans, and R. Kaaks Plasma Insulin-Like Growth Factor-I, Insulin-Like Growth Factor-Binding Proteins, and Prostate Cancer Risk: a Prospective Study J Natl Cancer Inst, December 6, 2000; 92(23): 1910 - 1917. [Abstract] [Full Text] [PDF]

				R. Kaaks, P. Toniolo, A. Akhmedkhanov, A. Lukanova, C. Biessy, H. Dechaud, S. Rinaldi, A. Zeleniuch-Jacquotte, R. E. Shore, and E. Riboli Serum C-Peptide, Insulin-Like Growth Factor (IGF)-I, IGF-Binding Proteins, and Colorectal Cancer Risk in Women J Natl Cancer Inst, October 4, 2000; 92(19): 1592 - 1600. [Abstract] [Full Text] [PDF]

				R. C. Jenkins, A. Meguid El Nahas, M. E. Wilkie, C. B. Brown, J. Jones, E. Ghigo, and R. J. M. Ross The Effects of Dose, Nutrition, and Age on Hexarelin-Induced Anterior Pituitary Hormone Secretion in Adult Patients on Maintenance Hemodialysis J. Clin. Endocrinol. Metab., April 1, 1999; 84(4): 1220 - 1225. [Abstract] [Full Text]

				M. E. Wilson Effects of Estradiol and Exogenous Insulin-Like Growth Factor I (IGF-I) on the IGF-I Axis during Growth Hormone Inhibition and Antagonism J. Clin. Endocrinol. Metab., November 1, 1998; 83(11): 4013 - 4021. [Abstract] [Full Text]