Comparison of insulin sensitivity in patients with insulinoma and obese Type 2 diabetes mellitus.

Insulin sensitivity was evaluated in 16 insulinoma patients and in 15 obese persons with Type 2 diabetes mellitus by using hyperinsulinaemic clamps and analysis of insulin receptor characteristics on erythrocytes. Significantly decreased insulin sensitivity index (M/l) was found in both insulinoma and obese Type 2 diabetic patients as compared with healthy non-obese controls (21.2 +/- 2.2 and 19.5 +/- 2.6 vs 40.3 +/- 3.7 mumol.kg-1.min-1 per mU.l-1 x 100, p < 0.001). No difference was observed between both groups of patients. Metabolic clearance rate of glucose was strongly reduced in obese diabetic patients but it was normal in insulinoma patients in comparison with healthy persons (2.7 +/- 0.4 vs 8.7 +/- 0.6 or 7.9 +/- 0.7 ml.kg-1.min-1, p < 0.001). A decreased insulin binding on specific receptors caused by reduced binding capacity was observed only in insulinoma patients but not in obese Type 2 diabetic patients. A significant negative correlation was proved between body mass index (BMI) and insulin sensitivity index (r = -0.82, p < 0.001) indicating that BMI is the main determining factor of insulin resistance in the total cohort of examined patients. We conclude that insulin resistance was caused by postreceptor changes in obese Type 2 diabetes, whereas a decreased insulin binding capacity together with post-receptor defect was present in insulinoma patients.