Incretin hormones in the treatment of type 2 diabetes. Part I: Influence of insulinotropic gut-derived hormones (incretins) on glucose metabolism

Abstract

Insulinotropic gut-derived hormones (incretins) play a significant role in the regulation of glucose homeostasis in healthy subjects and are responsible for 50-70% of insulin response to a meal. The main mediators of the incretin effect are glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). However, in patients with type 2 diabetes the effect of incretins action is to a large extent impaired, which seems to explain disturbed secretional activity of β cells in pancreatic islets. Detailed analysis of incretin defect proved that GIP secretion remains within physiological limits, whereas GLP-1 secretion is significantly decreased. Nevertheless, GLP-1 insulinotropic effect is preserved and GIP effect is significantly impaired. In consequence, substitutional GLP-1 administration aiming at the reduction of its deficiency, seems to be logical therapeutic management, because despite a physiologically retained quantity response from GIP, resistance to this peptide is frequently found. Therefore, particularly promising are the results of clinical studies with the use of GLP-1 analogues , GLP-1 receptors activation, as well as the inhibitors of dipeptidyl peptidase-IV (DPP IV), the enzyme responsible for incretin proteolysis, which restores the proper function of the intestinal-pancreatic axis in subjects with type 2 diabetes and creates new possibilities of a glycaemia reducing therapy and improvement in quality of life in this group of patients.