Analysis of Early-Phase Insulin Responses in Nonobese Subjects With Mild Glucose Intolerance

OBJECTIVE: To study the possible contribution of a B-cell defect in the development of glucose intolerance in nonobese subjects. RESEARCH DESIGN AND METHODS: There were 41 normal, nondiabetic subjects; 18 subjects with IGT; and 21 patients with NIDDM. All subjects were nonobese (BMI < 27 kg/m2). Insulin secretory responses to an OGTT, IVGTT, and GST were studied. RESULTS: Early-phase insulin responses to OGTT and IVGTT were decreased in subjects with IGT to levels comparable with those in NIDDM patients, whereas the response to GST was preserved in the subjects with IGT compared with NIDDM patients. The insulinogenic index of OGTT correlated well (r = 0.78) with early-phase insulin response to IVGTT, suggesting that the insulinogenic index in OGTT is related to the early-phase insulin response to IVGTT in nonobese subjects. CONCLUSIONS: Impaired early-phase insulin response to glucose was associated with mild glucose intolerance, suggesting the importance of impaired insulin secretion in the development of glucose intolerance in nonobese subjects.