Insulin response to paired oral and intravenous glucose loading were determined in 26 nonobese individuals classified as normal (nondiabetic control) subjects, mild to moderate diabetic subjects and borderline of these two categories.
All these subjects were previously divided into one of the three groups by 50 gram oral glucose tolerance test.
8 cases with diabetes had diabetic glucose tolerance and were confirmed to have diabetic microangiopathy.
Intravenous glucose tolerance test (IVGTT) was undertaken to determine eraly insulin response after intravenous glucose administration. Blood samples were collected from the antecubital vein before and 1, 2, 3, 5, 7, 10, 20, 30, 40, and 60 minutes after rapid glucose infusion of 0.33 g per kg of body weight. Blood glucose levels were determined by autoanalyser of Hoffman's method, and serum insulin levels were measured immunologically by modification of Hales and Randle's method.
Results are summarized as follows.
1) Decreased insulin response during 50 g oral glucose tolerance test in diabetic group was confirmed.
2) All three groups had peak blood glucose levels during IVGTT between 2 and 3 minutes after the infusion. The highest blood glucose levels were seen in diabetic group, and its k-value was 0.68. Nondiabetic control group had lower blood glucose levels with k-value of 2.0. Peak blood glucose levels in borderline cases were seen between normal control group and diabetic group, and mean of their k-value was 1.84.
3) Impaired insulin responses among diabetic group in early phase of IVGTT were noted andthis was significantly (p<0.01) lower than normal subjects.
But, peak insulin levels of borderline cases were not significantly higher than those of normal controls.
From these data, biological significance of impaired insulin response in early phase of IVGTT was discussed.
