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 erythrocyt es. Significantly decreased insulin sensitivity index (M/I) 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 m u mol . kg(-1) min(-1) per mU . l(-1) x 100, p<0.001). No difference w as 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 d ecreased insulin binding on specific receptors caused by reduced bindi ng capacity was observed only in insulinoma patients but not in obese Type 2 diabetic patients. A significant negative correlation was prove d between body mass index (BMI) and insulin sensitivity index (r = -0. 82, p<0.001) indicating that BMI is the main determining factor of ins ulin resistance in the total cohort of examined patients. We conclude that insulin resistance was caused by postreceptor changes in obese Ty pe 2 diabetes, whereas a decreased insulin binding capacity together w ith postreceptor defect was present in insulinoma patients.