Comparison of insulin secretion and insulin sensitivity between normal and impaired glucose tolerance subjects with normal fasting plasma glucose.

To examine glucose-stimulated insulin secretion and insulin sensitivity in the normal subjects and patients with impaired glucose tolerance, we performed the oral glucose tolerance test (OGTT) and modified insulin suppression test in 34 non-obese subjects. The plasma glucose and insulin concentrations were measured during fasting and every 30 min up to 120 min following 75 g of oral glucose loading. Ten subjects were classified as impaired glucose tolerance (IGT), and 24 subjects were as having normal glucose tolerance. In addition, the insulin-stimulated glucose uptake was estimated in all subjects by measuring the final 30 min steady-state plasma glucose (SSPG) of a continuous infusion of somatostatin, insulin and glucose for 4 hours (modified insulin suppression test). The mean plasma glucose concentrations of fasting and 60, 90, 120 min during OGTT study were significantly higher in the IGT subjects than in the normals. In addition, the mean incremental glucose areas under the curve during OGTT study were also greater in the IGT subjects than in the normals. The mean serum insulin concentrations were significantly higher at 90 and 120 minutes in the IGT patients than in the normals. During the modified insulin suppression test, the mean SSPG concentrations were significantly higher in the IGT patients than in the normals under the similar steady-state plasma insulin in both groups. There was a good correlation between the incremental insulin areas under the curve (OGTT) and the SSPG in the normal subjects (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)