Relationship between oral glucose tolerance and insulin sensitivity in healthy man and type 1 diabetic patients

The relationship between insulin sensitivity and oral glucose tolerance was studied in 8 conventionally treated type 1 diabetic patients (age 34 +/- 4 years, relative body weight (RBW) 113 +/- 5%) and in 11 healthy subjects (age 35 +/- 3 years, RBW 114 +/- 2%). In each subject and patient, oral glucose tolerance (75 g glucose) and in vivo sensitivity to insulin (euglycaemic clamp technique, 1 mU/kg/min insulin) were measured. The response to oral glucose in the diabetic patients was measured during maintenance of similar peripheral plasma free insulin levels as in the normal subjects during the oral glucose tolerance test (OGTT). During the OGTT, the post-glucose plasma glucose values in the diabetic patients were markedly higher (P less than 0.001) than in the normal subjects. During the clamp study, the rate of glucose metabolism in the diabetic patients (4.53 +/- 0.58 mg/kg/min) was 37% lower than in the normal subjects (7.19 +/- 0.67 mg/kg/min, P less than 0.02). The area under the glucose curve was inversely related to the rate of glucose metabolism in both the diabetic (r = -0.72, P less than 0.02) and the normal (r = -0.69, P less than 0.02) subjects. The slope of the curve was substantially steeper in the diabetic than the control subjects. Thus, peripheral insulin sensitivity contributes to oral glucose tolerance both in healthy man, and even to a greater extent, in type 1 diabetic patients.