The Effect of Defective Early Phase Insulin Secretion on Postload Glucose Intolerance in Impaired Fasting Glucose

Abstract

Abstract. Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are two risk groups for type 2 diabetes. Type 2 diabetes is characterized by both impaired insulin secretion and insulin resistance but their relative contribution to the development of hyperglycemia may differ due to heterogeneity of the disease. Combined glucose intolerance (CGI), on the other hand, seems to represent a more advanced stage of prediabetes that bears a distinctly higher risk of progression to diabetes and its comorbidities. This study has the aim to compare isolated IFG and CGI categories with respect to the degree of early phase insulin secretion abnormalities and insulin resistance. Subjects who had IFG (fasting glucose: 110-126 mg/dl) were included in the study. A 75-g oral glucose tolerance test (OGTT) with insulin response was done and subjects were classified according to the WHO criteria. Six subjects were excluded because they had diabetic glucose tolerance. A total of 66 patients (53.4 ± 11.1 years, female/male: 48/18) were divided into two groups according to their glucose tolerance in OGGT (Group 1: isolated IFG and group 2: CGI). Early phase insulin secretion was measured by intravenous glucose tolerance test (IVGTT) and OGTT. Insulin resistance was assessed by the R value of the homeostasis model assessment (HOMA). We did not find any statistically significant difference between groups according to age, gender, body mass index (BMI), fasting glucose, fasting insulin, insulin-AUC (0-180 min) and HOMA-R values. In OGGT there was no statistically significant difference between 0', 30', 60' and 90' insulin levels of the groups; only 120' and 180' insulin levels were higher in CGI than in IFG group (p<0.05). In IVGTT, there was no statistically significant difference between glucose levels of the groups. Furthermore, insulin response to intravenous glucose was higher in IFG than in CGI (p<0.05). Our data demonstrate that isolated IFG and CGI are similar with respect to the degree of insulin resistance, and that subjects with CGI had a more prominent deficit in early phases of insulin secretion.Key words: Impaired fasting glucose, Combined glucose intolerance, Early phase insulin secretion, Insulin resistance (Endocrine Journal 52: 531-536, 2005) TYPE 2 diabetes is characterized both by decreased insulin secretion and decreased insulin sensitivity, but the contribution of these factors to the etiology varies [1][2][3]. The relevance of insulin secretion abnormalities in the pathogenesis of type 2 diabetes mellitus has been extensively studied and a consensus has been reached. In order to fulfil its pivotal role in regulating glucose metabolism, insulin secretion must not only be quantitatively appropriate, but also possess qualitative, dynamic features that optimize insulin action on target tissues. In particular, increasing emphasis has been placed on the importance of the so-called first phase insulin secretion to glucose homeostasis [4]. Both impaired glucose tolerance (IGT) and impaired fasting glucose (I...

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