Glucagon-like peptide-1 profile during oral glucose tolerance test in young people

Abstract

Introduction. Currently, a major social problem is the occurrence of insulin resistance and metabolic disorders, which are risk factors for the development of type 2 diabetes. Particularly disturbing are the reports of an increasing number of such disorders in young people. The carbohydrate metabolism is regulated by neurohormonal mechanisms and insulin plays a major role in maintaining glucose homeostasis. Its secretion is determined by the current glucose concentration and the action of incretin hormones. The incretin effect describes the phenomenon whereby oral glucose elicits higher insulin secretory response than does the same intravenous glucose administration. This effect is visibly defective in patients with carbohydrate metabolism disorders. Objective. The aim of the study was to analyse the glucagon-like peptide 1 (GLP-1) concentration profile during the extended (three-point) oral glucose tolerance test (OGTT) and to assess its relationship to OGTT curve shape after 75 g glucose load and presence or absence of metabolic syndrome (MS) features in young, potentially healthy individuals. Material and methods. The study group consisted of 53 volunteers (40 women and 13 men) aged 19–28 years, with normal fasting blood glucose and normal glucose tolerance. Body mass, waist circumference, blood pressure, glucose, insulin, triglycerides, total and HDL cholesterol, GLP-1 and hsCRP concentrations were measured in the fasting state. Glucose, insulin and GLP-1 levels were also measured at 60 and 120 min after oral administration of 75 g of glucose. The results were analysed in subgroups based on the time required to return to fasting levels of blood glucose and the number of identified features of MS. Results. Comparison of the results obtained in the fasting state and at 60 and 120 min of the extended OGTT showed no significant differences in glucose and GLP-1 concentrations, whereas fasting plasma insulin concentrations were significantly lower than those observed at 60 and 120 min of the OGTT. Neither the time for blood glucose to return to fasting values nor the number of metabolic syndrome features were associated with significant differences in GLP-1 concentrations between the groups analysed at any of the measurement points (fasting state, 60 and 120 min of the OGTT). Only the tendency to lower GLP-1 values was observed in the group of patients with the MS. Conclusions. Our observations may suggest that GLP-1 level measurements are not useful in determining the insulin response profile after glucose oral administration in young people without apparent carbohydrate disorders, but they may indicate disturbances in the incretin effect in subjects with MS. Our study will be continued with a larger number of volunteers to provide a more detailed mechanism of the regulation of insulin secretion by incretins and the potential role of GLP-1 in the development of MS in young people.