Aim:  This study was designed to assess the usefulness of a model‐based index of insulin sensitivity during an oral glucose tolerance test (OGTT) in the identification of possible changes in this metabolic parameter produced by pharmacological agents known to be potent insulin sensitizers, that is metformin (M) and thiazolidinedione (T). The association of these agents with several other factors related to glucose metabolism was also investigated, as well as the relation of insulin sensitivity and secretion with markers of endothelial function such as different adhesion molecules (cAMs), that is vascular cell adhesion molecule‐1, intercellular adhesion molecule‐1 and E‐Selectin.

Methods:  Twenty type 2 diabetic patients treated with diet only underwent a 3‐h OGTT for measurement of plasma glucose, insulin, proinsulin, C‐peptide and cAMs before and after administration of randomly given M (n = 9; 1700 mg/day) or T (n = 11; 600 mg/day). After 16 weeks of treatment, a second OGTT was performed. Insulin sensitivity was calculated with homeostasis model assessment and with oral glucose insulin sensitivity (OGIS), which quantifies dynamic glucose clearance per unit change of insulin. Insulin secretion was assessed by modelling technique. Differences in these parameters before and after treatment, as well as possible relationships with cAMs, were assessed.

Results:  Basal and stimulated plasma glucose decreased after therapy in both the groups by approximately 20%. Basal insulin resistance also decreased. Insulin sensitivity in dynamic conditions (OGIS: ml/min/m²) increased with M (289.3 ± 18.8 vs. 234.7 ± 18.1, p < 0.02) and tended to improve with T (323.5 ± 18.1 vs. 286.8 ± 22.1, p = 0.09). Total insulin secretion over the OGTT [TIS: nmol/l(3 h)] tended to decrease with M (17.1 ± 2.5 vs. 27.3 ± 0.3, p = 0.08) but not with T (23.6 ± 3.5 vs. 22.5 ± 2.7). Plasma concentrations of E‐Selectin decreased in T (38.0 ± 2.3 vs. 51.2 ± 6.1 ng/ml, p < 0.05). No correlation was found between insulin sensitivity and cAMs.

Conclusions:  Model‐based indices of insulin sensitivity and secretion during an OGTT can be able to detect changes observed in patients under treatment with pharmacological agents such as M or T. Both the drugs improved glucose control similarly. Decreased plasma E‐Selectin concentrations were seen in patients on T therapy only.