Istituto di Fisiologia Clinica     
Ferrannini E., Gastaldelli A., Miyazaki Y., Matsuda M., Pettiti M., Natali A., Mari A., Defronzo R. A. Predominant role of reduced beta-cell sensitivity to glucose over insulin resistance in impaired glucose tolerance. In: Diabetologia, vol. 46 pp. 1211 - 1219. springer, 2003.
Aims/hypothesis Impaired glucose tolerance (IGT) is an insulin-resistant state and a risk factor for Type 2 diabetes. The relative roles of insulin resistance and insulin deficiency in IGT have been disputed. Methods In 40 IGT subjects and 63 sex-, age-, and weight-matched controls with normal glucose tolerance (NGT), we measured (i) indices of insulin sensitivity of fasting glucose production (by tracer glucose) and glucose disposal (M value on a 240 pmol·min-1·m-2 insulin clamp) and (ii) indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) derived from model analysis (Am J Physiol 283:E1159-E1166, 2002) of the insulin secretory response (by C-peptide deconvolution) to oral glucose. Results In comparison with NGT, IGT were modestly insulin resistant (M=29±2 vs 35±2 µmol·min-1·kgFFM-1, p=0.01); insulin sensitivity of glucose production also was reduced, in approximate proportion to M. Despite higher baseline insulin secretion rates, IGT was characterized by a 50% reduction in glucose sensitivity [53 (36) vs 102 (123) pmol·min-1·m-2·mM-1, median (interquartile range), p=0.001] and impaired potentiation [1.6 (0.8) vs 2.0 (1.5) units, p<0.04] of insulin release, whereas rate sensitivity [1.15 (1.15) vs 1.38 (1.28) nmol·m-2·mM-1] was not significantly reduced. Glucose sensitivity made the single largest contribution (~50%) to the observed variability of glucose tolerance. Conclusion/interpretation In IGT the defect in glucose sensitivity of insulin release quantitatively predominates over insulin resistance in the genesis of the reduced tolerance to oral glucose.
URL: http://www.springerlink.com/content/7mgfak1py72u61qj/fulltext.pdf
Subject IGT
beta-cell function
insulin secretion

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