Summary
A new modelling analysis was developed to assess insulin sensitivity with a tracer-modified intravenous glucose tolerance test (IVGTT). IVGTTs were performed in 5 normal (NGT) and 7 non-insulin-dependent diabetic (NIDDM) subjects. A 300 mg/kg glucose bolus containing [6,6-2H2]glucose was given at time 0. After 20 min, insulin was infused for 5 min (NGT, 0.03; NIDDM, 0.05 U/kg). Concentrations of tracer, glucose, insulin and C-peptide were measured for 240 min. A circulatory model for glucose kinetics was used. Glucose clearance was assumed to depend linearly on plasma insulin concentration delayed. Model parameters were: basal glucose clearance (Clb), glucose clearance at 600 pmol/l insulin concentration (Cl600), basal glucose production (Pb), basal insulin sensitivity index (BSI = Clb/basal insulin concentration); incremental insulin sensitivity index (ISI = slope of the relationship between insulin concentration and glucose clearance). Insulin secretion was calculated by deconvolution of C-peptide data. Indices of basal pancreatic sensitivity (PSIb) and first (PSI1) and second-phase (PSI2) sensitivity were calculated by normalizing insulin secretion to the prevailing glucose levels. Diabetic subjects were found to be insulin resistant (BSI: 2.3 ± 0.6 vs 0.76 ± 0.18 ml · min–1· m–2· pmol/l–1, p < 0.02; ISI: 0.40 ± 0.06 vs 0.13 ± 0.05 ml · min–1· m–2· pmol/l–1, p < 0.02; Cl600: 333 ± 47 vs 137 ± 26 ml · min–1· m–2, p < 0.01; NGT vs NIDDM). Pb was not elevated in NIDDM (588 ± 169 vs 606 ± 123 μmol · min–1· m–2, NGT vs NIDDM). Hepatic insulin resistance was however present as basal glucose and insulin were higher. PSI1 was impaired in NIDDM (67 ± 15 vs 12 ± 7 pmol · min–1· m–2· mmol/l–1, p < 0.02; NGT vs NIDDM). In NGT and in a subset of NIDDM subjects (n = 4), PSIb was inversely correlated with BSI (r = 0.95, p < 0.0001, log transformation). This suggests the existence of a compensatory mechanism that increases pancreatic sensitivity in the presence of insulin resistance, which is normal in some NIDDM subjects and impaired in others. In conclusion, using a simple test the present analysis provides a rich set of parameters characterizing glucose metabolism and insulin secretion, agrees with the literature, and provides some new information on the relationship between insulin sensitivity and secretion. [Diabetologia (1998) 41: 1029–1039]
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Received: 17 September 1997 and in final revised form: 28 April 1998
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Mari, A. Assessment of insulin sensitivity and secretion with the labelled intravenous glucose tolerance test: improved modelling analysis. Diabetologia 41, 1029–1039 (1998). https://doi.org/10.1007/s001250051027
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DOI: https://doi.org/10.1007/s001250051027